This document provides an overview of bacteriology concepts including definitions of aerobic and anaerobic bacteria. It discusses specimen collection and transport for aerobic bacteriology as well as the Gram stain procedure. Common aerobic agar media and identification of Gram positive cocci such as Staphylococcus, Streptococcus, and Enterococcus are summarized. Key details are provided about pathogenic species and their associated diseases.

1. Bacteriology Review

2. Beginning definitions
• Obligate Aerobe – require oxygen (20%) to grow
• Obligate Anaerobe –>30 min of oxygen exposure can be toxic
• Facultative anaerobes – grow in aerobic and anaerobic
conditions, most “aerobic” bacteria are actually facultative
• Microaerophilic – Grow better with reduced oxygen and
elevated Carbon dioxide %
• Aerotolerant anaerobes– anaerobe not killed by prolonged
exposure to oxygen – example: Clostridium tertium
• Lag Phase - >24 hrs old, growth slowing, not appropriate for
biochemical or susceptibility testing
• Log Phase – Exponential growth – appropriate for all testing
• Stationary phase – appropriate for transporting specimens

3. Specimen collection
for Aerobic Bacteriology
Throat / Wound collected using swab
1. Swab placed in Stuart’s or Amies transport media buffer
solution with peptones –
2. Preserve viability but not promote growth of bacteria
3. Swabs made of polyester or sponge like material, cotton
traps organisms/potentially toxic
Urine – two methods suggested
1. Boric acid to place organism in stationary phase
2. Refrigerate within one hour, Specimen stable for 24 hours
• Purpose to maintain original colony count
• Maintain viability of organisms

4. Gram stain Procedure
10 seconds-
1 minute
Primary stain
Mordant 10 seconds-
1 minute
Rinse
5-10 seconds
Rinse
Rinse
Decolorization
Counter stain 10 seconds-
1 minute
Peptidoglycan in positive cell wall traps the Crystal violet, hence blue color

5. Gram positive cocci
in pairs and chains
Streptococcus
Gram negative
bacillus
Resembling an
Enteric
Gram positive rod
most likely a
Bacillus species
Gram positive cocci in clusters,
Staphylococcus
Gram negative rod – Fusiform
Shaped – Fusobacterium
species
Some Gram stains to
remember! Visit the Gram
stain Tutorial for more
organisms!

6. Gram stain is used to assess quality of
Sputum specimen for culture
• Expectorated sputum specimen is rejected for bacterial
culture if judged to be “spit”:
– Perform Gram stain of sputum specimen
– If >= 25 epithelial cells /field
– Sputum is judged to be spit / not a sputum specimen
– Bacterial culture is not performed / it is rejected
– Request made for a new “deep cough” specimen
Bad Sputum Good
Sputum
10X objective 10X objective

7. Most used Agar Media in Bacteriology
Blood agar- 5% sheep’s blood agar
Gauge hemolytic reaction of bacteria (alpha, beta, gamma)
Grow variety of Gram positive & Gram negative bacteria and
Yeast
Chocolate agar – “carmelized” blood agar – more enriched than
blood agar medium. Will support the growth of the same
organisms as blood agar Plus the more fastidious bacteria
like Haemophilus influenzae and Neisseria gonorrhoeae

8. Most used agar media in Bacteriology
• MacConkey agar – Supports growth of Gram negative rods
(GNR) only (crystal violet inhibits Gram positive organisms)
Selective (only GNR grow ) and Differential (Lactose
fermentation can be determined)
Lactose fermentation = pink (neutral red indicator) (+)
non-lactose fermentation = no color (-)
• After media is plated incubate in aerobic and/or CO2
incubators at 35˚ C for 24 – 72 hours

9. Newest Method for Organism
Identification
• MALDI-TOF mass spectrometry
– Matrix-assisted laser desorption/ionization
– Identification of organisms by analyzing proteins

10. Gram Positive Cocci
Staphylococcus
Streptococcus
Enterococcus

11. Staphylococcus
Gram positive cocci inclusters
due to bound coagulase or “clumping factor”
All Staphylococcus are Positive for Catalase Enzyme
Staphylococcus aureus Coagulase Negative Staph
Coagulase Enzyme Positive Coagulase Enzyme Negative
+/- Yellow colony
Beta hemolysis
White colony
Most not hemolytic

12. Catalase Enzyme Reaction
Negative Positive
Hydrogen Peroxide plus bacteria
Avoid blood agar when collecting Staph –
blood has innate catalase activity and will
give false positive catalase reaction

13. Rabbit plasma inoculated with organism
Incubate at 35˚C
Read at 4 hours and if negative read again at 24 hours
Negative tube coagulase =no clot
Coagulase negative Staph
Positive tube coagulase [at 4 or 24 hrs] =
Clot = Staph aureus
Tube Coagulase Reaction

14. Slide Agglutination Test to identify
Staphylococcus aureus
• Clumping factor (coagulase) and protein A is found on the S. aureus cell wall.
• Fibrinogen and IgG to protein A is on the surface of the Staphaurex latex beads
• S. aureus will clump in the Staphaurex latex bead solution and
positively identifies Staphylococcus aureus.
• Coagulase negative Staphylococcus species remain milky and do not clump in
the solution.
•Advantage over tube coagulase – reaction time is 30 seconds vs. 24 hours
clumping
No clumping

15. Staphylococcus aureus
• Primary virulence factor:
– Protein A – surface protein, ability to bind immunoglobulin and
combat the immune response
• Diseases and associated toxin:
– Toxic shock syndrome (TSST-1 toxin)
– Scalded skin syndrome (Exfoliatin (SSS) toxin)
– Soft tissue infection (Panton valentine leucocidin toxin – PVL)
– Septic arthritis – primary cause
– Food poisoning / Enterotoxins – stable to
heating at 100*C for 30 minutes
– Bacteremia and endocarditis
• Toxins act as superantigens, recruit host
defense cells that liberate cytokines with
systemic effects

16. Susceptibility issues –(1) MRSA
• Methicillin Resistance (MRSA =Methicillin resistant S. aureus)
– Altered Penicillin binding protein (PBP2) produced by the mecA gene
codes for resistance to oxacillin/methicillin/nafcillin
– All MRSA are considered resistant to semisythetic penicillins and
cephalosporins
– Vancomycin is drug of choice – although reduced susceptibility
reported
– Cefoxitin susceptibility testing is considered a more sensitive indicator
of resistance and provides better detection of MRSA than oxacillin
testing. Shown is a Kirby Bauer (KB) disk test that is resistant to
cefoxitin.

17. (2) The “D” Test
• To accurately determine if Staph aureus/MRSA is susceptibleTo accurately determine if Staph aureus/MRSA is susceptible
to Clindamycinto Clindamycin
• During therapy, S aureus isolates resistant to ErythromycinDuring therapy, S aureus isolates resistant to Erythromycin
possess enzymes capable of inducing Clindamycin to becomepossess enzymes capable of inducing Clindamycin to become
resistant and therefore not useful for therapy.resistant and therefore not useful for therapy.
• Kirby Bauer zone around Clindamycin will be blunted to formKirby Bauer zone around Clindamycin will be blunted to form
a “D” if Clindamycin can be induced by Erythromycin to bea “D” if Clindamycin can be induced by Erythromycin to be
resistant – so called INDUCIBLE RESISTANCE.resistant – so called INDUCIBLE RESISTANCE.
• Clindamycin should be reported as resistant by clindamycinClindamycin should be reported as resistant by clindamycin
induction and not used for therapy.induction and not used for therapy.
D test positive
Inducible
resistance
D test negative
Clindamycin can
be used for
therapy

18. Nares is a colonization site for MRSA and the
most common surveillance site cultured.
ChromAgar is commonly used to detect MRSA.
It is a selective and differential media with
chromogenic substrates that turn specific colors
to ID Staph aureus. Cefoxitin is added to the
medium to select for methicillin resistant Staph
aureus (MRSA).
Molecular assays (MA) can also be used to
screen nares for MRSA. MAs increase the
sensitivity of detection (@5-10%) but increases
laboratory costs.
Mupiricin can be used to eliminate carriage
Staphylococcus aureus (MRSA)
Hospital Epidemiology Issue:
Nasal surveillance for MRSA

19. Coagulase negative Staph (CNS)
@ 15 species infect humans
• Staph epidermidis – is the most common
– Major aerobic component of normal skin flora
– Common cause of subacute bacterial endocarditis
– Pathogenicity from cell adhesion factors forming
biofilm on biologics and plastic
(Catheters and replacement joints) – can be
difficult to treat
• Staph saprophyticus –
– Urinary tract infections in the child bearing age female,
– This species of CNS adheres in greater #’s to epithelial cells
– Novobiocin resistant by KB disk test can be used as test to identify
Staph saprophyticus
White non-hemolytic
colony
resistant

20. CNS & Related Cocci
• Staph hemolyticus –
– Can cause line related sepsis
– This CNS is hemolytic on blood agar
– Do not confuse with Staph aureus
• Staph lugdunensis
– Positive PYR test
– Perhaps greater pathogenicity than other species
• Micrococcus species
– Mustard yellow colored colony
– Catalase positive / Gram positive cocci in tetrads
– Tube coagulase negative
– Does not ferment glucose
• Staphylococcus ferment glucose
– Environmental contaminate
Pos Neg

21. Streptococcus
Gram positive cocci in chains and pairs
Catalase enzyme negative
Grouped by hemolytic pattern on 5% sheep’s blood agar
– Alpha – greening of agar, partial hemolysis of RBCs
• Viridans Streptococcus, Strep pneumoniae,
Granulicatella/Abiotrophia
– Beta – clearing of agar, complete hemolysis of RBCs
• Beta hemolytic Streptococcus groups A - G
– Gamma – no clearing of agar, intact RBCs
• Streptococcus bovis (gallolyticus)

22. Beta hemolytic
Streptococcus
• Beta Streptococcus are grouped using the “C” (CHO)
carbohydrate in the cell wall of the bacteria
• Identifies the Beta Strep groups – A, B, C, F, and G that are
most common cause of human infections
• Lancefield grouping system uses the “C” CHO in the cell
wall of Streptococcus (antigen) in a slide agglutination
reaction with purchased monoclonal antibody attached to
latex beads
See below slide for a positive and negative reaction.
• Immunologic typing is more accurate than biochemical
testing to group Streptococcus +
-

23. Streptococcus pyogenes
• Genus/species for Group A beta Streptococcus [GAS]
Biochemical identification:
– Bacitracin KB sensitivity test – inhibited, no growth @ disk
– This test is not specific for Group A , it x-reacts with group C
– “A” disk is the Bacitracin disk
– PYR (pyrrolidonyl arylmidase) reaction
• Organism spotted on moist disk
• 2 min – RT incubation
• Add Cinnamaldehyde reagent
• Look for color reaction
• Pink = positive = Strep pyogenes
• This test is not exclusive for Strep pyogenes – Enterococcus and
Staph lugdunensis are also positive for PYR
– Therapy : Penicillin or Cephalosporin antibiotics

24. – Streptolysin O and Streptolysin S toxins
• Comprise the ASO titer dtermination
• Cell toxins lead to evasion from the immune system
• O toxin is oxygen labile S toxin is oxygen stable
• When both are active - most hemolysis occurs in the 5% Sheep’s
blood agar
Primary virulence factors:
M Protein – prevents
phagocytosis
Capsule – hyaluronic capsule
protects from phagocytosis

25. Streptococcus pyogenes Diseases
• Diseases –
– Pharyngitis
– Impetigo (1)
– Erysipelas (2)
– Cellulitis (3)
– Necrotizing fascitis (4)
– Puerperal sepsis
– Toxic Shock
– Scarlet fever (5)
1
2
3
4
5

26. Sequelae of Strep pyogenes
infections
• Rheumatic fever
– Cause: inadequately treated Strep throat
– Rise in the 1990s due to EIA tests being used as the only diagnostic test for
pharyngitis – EIA tests are @ 60-70% sensitive – and led to children not
receiving antimicrobial therapy. All negative EIA specimens on children
must be confirmed with culture
– Similarity between the proteins of the Strep A and muscle tissue cause
immune system confusion which leads to immune system to attack heart,
joint, and bones
– Anti-streptolysin O measures the amount of antibodies against
Streptococcus group A in the serum
• Glomerulonephritis
– 10-14 days following skin infection or pharyngitis
– Renal disease with inflammation of the glomeruli
– ASO titers will be positive
– Usually resolves with therapy

27. Streptococcus agalactiae (Group B)
Lancefield agglutination test demonstrates “B” cell wall CHO
Biochemical tests for identification:
Camp test – performed using a Staph aureus strain with Camp
factor streaked perpendicular to group B Strep, incubate 24
hr. / intensifies toxin and produces arrow shaped hemolysis
Rapid hippurate hydrolysis -
4 hr identification of GBS - Hippurate disk in
Saline inoculated with Group B Strep
Ninhydrin reagent added for color formation
Positive = Purple
pos
Arrow-like
Staph aureus
Strep group B

28. Strep agalactiae [GBS]
• Pathogen of the elderly – mostly bacteremia and urinary tract infection
• Pathogen of neonate – in utero or perinatal organism acquisition during
birthing process
– Early onset – within 7 days
– Late 7 – 28 days from birth process.
• Treatment: Penicillin or Cephalosporin (3rd
generation)
• Pregnant women carry organism in the cervix and/or rectal area. All
pregnant should be tested at 35 – 37 weeks of pregnancy.
– Enrichment methods for GBS is standard of practice and must be used
• Swab placed into LIM broth – incubate for 18 hours at 35 ˚C then
subculture onto Blood agar. This broth can also be used as an enrichment
method to enrich for molecular testing.
• Carrot enrichment broth turns orange with growth of group B Strep
Carrot Broth

29. It used to be Streptococcus bovis
Taxonomy update – S. gallolyticus
1) Streptococcus gallolyticus ssp. gallolyticus (formerly S. bovis
biotype 1) associated with colonic cancer and endocarditis
2) Strep gallolyticus ssp. pasteurianus (formerly S. bovis
biotype II) associated with neonatal meningitis
S. gallolyticus (both ssp) have same biochemical reactions
B

30. • Two most common species
– E. faecium
– E. faecalis
• No well defined virulence factors
• Possesses the Group “D” CHO in the cell wall
• Biochemical tests:
– Bile esculin positive – growth and black precipitin
– Growth in 6.5% salt
– PYR positive (Group A beta Strep and Staph
lugdunensis also positive)*
– E. faecium = arabinose fermentation positive
– E. faecalis = arabinose fermentation negative
Enterococcus
Bile esculin
PYR
+ -
Neg Pos
Neg Pos
6.5% Salt
PYR

31. Enterococcus
• Variety of infections / Pathogen of opportunity
• Intestinal normal flora
• Cause UTI, bacteremia, and abdominal infections
• Antimicrobial therapy:
– Natural resistance to cephalosporin antibiotics
– Ampicillin plus Aminoglycoside can be synergistic for therapy in
cases of endocarditis
• Unique susceptibility issues
– Acquired resistance to vancomycin known as vancomycin resistant
enterococcus or VRE
• Van A (E. faecium) resistance genes
• Van B (E. faecalis) resistance genes

32. Alpha hemolytic
Streptococcus
Streptococcus pneumoniae
Gram stain = Gram positive bullet (lancet) shaped cocci in pairs
Polysaccharide capsule = virulence factor, antiphagocytic
Identification:
– Bile soluble – colonies dissolve in sodium deoxycholate (bile)
– Optochin sensitive – 14mm or greater zone of inhibition around the
6mm optochin disk – “P” = pneumococcus
Inhibition
>=14mm
NO
Inhibition
Colonies dissolved

33. Streptococcus pneumoniae
• Upper and Lower respiratory tract infection, sepsis and
meningitis
• Multi-serotype vaccine aids preventing invasive infections
• Susceptibility issues:
– Acquired Resistance to Penicillin due to Penicillin binding
proteins (PBP)
– Minimum inhibitory concentration (MIC) testing necessary
to detect resistance to penicillin – in broth or Etest method
– Testing of CSF isolate a result of
– Penicillin = >2 mcg/ml is resistant
• Therapy –
– If susceptible 1st
line therapy is either
– Penicillin or 3rd
generation Cephalosporin
MIC
MIC

34. Viridans Streptococcus
Several species of alpha hemolytic Streptococcus are NF in
mouth and upper respiratory tract
S. mutans S. salivarius S. sanguis S. mitis
• Bile esculin slant = negative
• Not bile soluble
• Optochin resistant with zone size <=13 mm
• Cause 30 – 40% cases of sub acute endocarditis / native valve
• Can cause abscess and various infections throughout the body
especially in the immune suppressed host
• Variable susceptibility patterns, some isolates with elevated
MICs to Penicillin
Viridans Streptococcus

35. Viridans Streptococcus
unique species
• Streptococcus anginosis group: includes
– S. anginosus S. constellatus S. intermedius
• Normal flora in human mouth
• More virulent than “normal” viridans
Streptococcus, perhaps due to capsule
• Cause deep tissue abscess, bacteremia,
endocarditis, intra abdominal infections…
• Variable susceptibilities – so best to do
susceptibility testing

36. Nutritionally Variant Streptococcus
• Vitamin B6 (pyridoxal) deficient – so will not grow on media without B6
supplementation
• Will grow in a patient blood culture bottle due to vit B6 in patient’s blood
• Will not subculture onto 5% Sheep’s blood agar plate ( no vit B6)
• Requires Staph aureus streak (supplies vitamin B6)
• Nutritionally variant Strep will satellite @ S. aureus streak (see pix)
• There are 2 species:
– Abiotrophia spp
– Granulicatella spp
• Endocarditis –
– More destructive to valve than
than “regular” viridans Strep
– Higher MIC’s to Penicillin
Satellite streptococcus

37. Gram Negative Cocci
Neisseria
Moraxella

38. Gram Negative Cocci
• Neisseria species and Moraxella catarrhalis
– Small kidney bean shaped cocci in pairs
– Oxidase enzyme positive
• CTA (Cysteine Trypticase Agar) carbohydrate fermentations
for identification – glucose, maltose, lactose, sucrose
– N. gonorrhoeae Gluc + Mal - Lac - Suc -
– N. meningitidis Gluc + Mal + Lac - Suc -
– N. lactamica Gluc + Mal + Lac+ Suc-
– M. catarrhalis all negative Dna’ase +
• N. gonorrhoae will NOT grow on 5% Sheep’s blood agar
• N. meningitids will grow on 5% Sheep’s blood agar

39. Miniature CHO fermentation reactions for Neisseria
and Moraxella catarrhalis
Compare (+) yellow reactions to negative (red) control well
+
+ +
Oxidase enzyme spot test:
Detects presence of enzyme cytochrome
oxidase Add reagent
N,N dimethyl-p-phylenediamine oxalate
to filter paper with organism
positive = purple/ blue
control
Full size tube CHO fermentation test

40. Neisseria meningitidis
• Meningitis in children and young adults
• Hallmark is petechia (organisms crowd into capillaries) tissue
necrosis and DIC (endotoxin) /infection can be rapidly fatal
• Carriage in Nasopharynx/ Susceptible to Penicillin
• Capsular polysaccharide is the primary virulence factor
• Complement deficiencies in 7,8,and 9 can predispose to
chronic type disease
• Adrenal necrosis is referred to Waterhouse
Friderichsen syndrome
• Type C is the current endemic strain in the USA – 1*problem
in college Freshmen living in dorm
• Immunization available for all serotypes except serotype B

41. Neisseria gonorrhoeae
– Acute urethritis, endocervix, ocular, rectal, oropharynx,
septic arthritis
– 10 – 20 % female ascend to PID but only 0.5% disseminate
– Gram stain of urethral discharge useful for male diagnosis,
however, cervix Gram stain not specific for females
– Transport for culture – charcoal swabs, No refrigeration
– Media: Selective Thayer Martin or Martin Lewis agar
– Amplification methods [PCR] increase sensitivity of
detection and superior to culture
– Produces a beta lactamase enzyme and also Chromosomal
resistance : Therapy: Ceftriaxone + Azithromycin or Doxycycline to prevent
resistance

42. Neisseria species
gram negative diplococcus – intra and
extra cellular
Acinetobacter species –
Cocci are larger and more round
than Neisseria, not usually in pairs –
normal flora in female genital tract
Primary reason why female Gram stains
Cannot be trusted.

43. Moraxella catarrhalis
• Pneumonia, ocular, sinusitis, otitis media
• Gram stain of sputum can be helpful in
diagnosis of Moraxella pneumonia
– Polys with gram negative diplo-cocci
• Hockey puck colony – able to push
around on agar surface
– Oxidase enzyme positive
– DNA’ase enzyme positive
– Resistant to ampicillin by beta lactamase enzyme
production – Cefinase test can be used
– Therapy: Augmentin or 2nd
or 3rd
generation Cephalosporin

44. Gram Positive Rods
Corynebacteria
Bacillus
Listeria
Erysipelothrix

45. Corynebacterium
•Over 20 species, most not pathogenic
•Gamma hemolytic gray colonies
•Catalase +
•Diphtheroid morphology – Gram positive
Chinese letter forms
•No spores produced

46. Corynebacterium diphtheriae
• Agent of Diphtheria
• Diphtheritic adherent pseudo membrane produced in throat
• Phage mediated exotoxin is distributed from the membrane
causing respiratory paralysis (virulence factor)
• Toxin detected by Elek immuno-diffusion test
• Grows well on 5% Sheep’s BAP
• Selective medium Cysteine Tellurite agar
– Produces black colonies with brown halos
• Grow on egg containing Loeffler medium then stain
with methylene blue to observe metachromatic
granules - colorful storage granules characteristic of C.
diphtheria
Elek plate
Tellurite agar
Metachromatic granules

47. Other Corynebacterium
• Corynebacterium jeikeium –
– normal skin flora bacteria / thrives on lipid
– Infects patients with plastic catheters and indwelling
devices by tunneling into the device from the skin
– Biofilms are formed on the plastic, protecting the
organism from antibiotic therapy
– Very resistant to most antibiotics
– Susceptible to vancomycin and tetracycline only
• Corynebacterium urealyticum –
– Rapidly urease positive diphtheroid
– Urinary tract infection in post renal transplants
– Resistant to many antibiotics – vancomycin susceptible
Red is (+) for
Urease reaction

48. Bacillus species
• Large gram positive rods boxcar shaped with square
ends
• Can over-decolorize easily and appear reddish
• Spores produced – causes clearing in rod
• Catalase enzyme positive
• Most are motile

49. Bacillus anthracis
• Agent of Anthrax
• Natural infection of herbivores – infected animals can have
fatal infection and contaminate the environment for years
• Virulence factors: anthrax toxin and capsular polypeptide
• Skin (Woolsorters’ disease) is the most common
presentation
• Unique black eschar skin lesions
• Pneumonia, sepsis, and meningitis
uncommon

50. Bacillus
• Bacillus anthracis culture:
• Medusa head colonies on BAP
– non-hemolytic on 5% Sheep’s blood agar
• Non-motile
• Penicillin susceptible
• With these reactions – Alert public health
department for assistance
• Bacillus cereus – food poisoning with rapid
onset (1 – 6 hr) of vomiting
• Preformed emetic toxin in food
• Fried rice is one of the most common food sources
• Traumatic wound infection from contaminated soil
• Beta hemolytic colony on Sheep’s blood agar
• Motile

51. Listeria monocytogenes
• Small gram positive rod
• Catalase positive / No spores produced
• Subtle beta hemolysis on Blood agar
• Tumbling motility on wet mount
• Umbrella motility in tube media
• More motile at 25˚C than 35˚C
• Cold loving – Grows well at 4˚C and reason it is
abundant in refrigerated foods
• Found in dairy products and deli case meats
• Infections: Bacteremia in pregnant women and
can induce still births
• Infections: Bacteremia and CNS in immune suppressed
• Ampicillin is drug of choice/ resistant to Cephalosporins

52. Erysipelothrix rhusiopathiae
• Small gram positive rod
• Catalase enzyme negative
• Alpha hemolysis on blood
– Only G+R that produces hydrogen
sulfide (H2S) in a TSI agar slant
– Human skin infection acquired from swine with erysipelas or
poultry
• Infection most common in butchers
– Bacteremia uncommon
• most common in drug addict
• High % of endocarditis with extensive damage to valve
– Intrinsically resistant to Vancomycin
H2S production on
Triple sugar iron agar (TSI)

53. Gram negative bacilli
Enterics
Non fermenters
Fastidious

54. Gram negative cell
Wall
Rod shaped
Simple flow chart
Identification
Strategy
Enteric Gram
Negative Rod
Ferment Glucose
Ferment Lactose
Ex. Escherichia
coli
Enteric Gram
Negative Rod
Ferment Glucose
Do NOT ferment
Lactose
Ex. Proteus species
Gram negative Bacilli
Do NOT ferment
Glucose
Do not ferment
Lactose
Positive Oxidase
Pseudomonas
Burkholderia
Gram negative Bacilli
Do NOT ferment
Glucose
Do NOT ferment
Lactose
Negative Oxidase
Acinetobacter
Stenotrophomonas
Enterobacteriaceae
Enteric Gram Negative Bacilli
Ferment glucose
Almost all are oxidase negative
Nitrate reduced to nitrates
Non fermenters
Glucose is not fermented
Oxidase positive and
negative
species

55. Enterics that Ferment Glucose
• Escherichia coli
– Major aerobic NF in intestine
– #1 cause of UTI [@80%]
– Bacteremia, neonatal meningitis
– Abdominal cavity infections
– Spot indole reaction = positive
– Green sheen produced on EMB agar
• Pathogen of diarrhea
– Traveler’s diarrhea - travel to developing countries
– Enterohemorrhagic E. coli [0157:H7 as well as other serotypes]
• Bloody diarrhea usually acquired from eating undercooked cow
meat from an infected cow
• HUS – hemolytic uremic syndrome [hemolytic anemia,
thrombocytopenia, and renal failure] particularly in children
• Does not ferment sorbitol – most other E. coli types ferment
Sorbitol
Green sheen on
EMB agar
Mucoid colony
Indole positive =
Robin’s egg blue

56. Enterics that ferment Glucose
• Enterobacter species
• Enterobacter cloacae and E. aerogenes most common
• Environmental organism with low pathogenicity
• Enterobacter (Cronobacter) sakazakii associated with
neonatal meningitis
• Klebsiella species –
• K. pneumoniae most common
• Mucoid colony
• Currant jelly sputum in alcoholics due to blood mixed with
capsular polysaccharide in sputum

57. Enterics that do NOT ferment lactose!
No fermentation = colorless colony on Mac
• Proteus species
Swarming colonies in layers on agar surface
• Indole positive – Proteus vulgaris
• Indole negative – Proteus mirabilis
• Serratia marcescens
– Produces a red pigment that intensifies at room temp
– Causes infections in
• immune suppressed
• Ventilator associated pneumonia
• Bacteremia

58. Gram negative bacillus
MacConkey agar
Lactose fermenter
Lactose non
fermenter
Gram stain enteric
bacilli – plump
No lactose
fermentation
Lactose fermentation

59. Glu/lac/suc
fermented
with gas
Glucose
fermented
only
Glucose
fermented
with H2S
No CHO
fermentation
Non fermenter
Triple Sugar Iron Agar – Detect fermentation of
glucose, lactose and/or Sucrose and the
production of hydrogen sulfide [H2S]
Fermentation= yellow
Gas = Disruption of the agar
H2S
No fermentation =
red

60. Extended Spectrum Beta LactamaseExtended Spectrum Beta Lactamase
Enzymes – “ESBL”Enzymes – “ESBL”
• ESBL enzymes are produced by numerous species of gramESBL enzymes are produced by numerous species of gram
negative rodsnegative rods
– These enzymes confer resistance to Cephalosporins andThese enzymes confer resistance to Cephalosporins and
synthetic Penicillinssynthetic Penicillins
• Plasmid mediated Tem 1 beta lactamase is the most commonPlasmid mediated Tem 1 beta lactamase is the most common
ESBL enzyme producedESBL enzyme produced
– Possible plasmid dissemination makes this an infectionPossible plasmid dissemination makes this an infection
control issuecontrol issue
• ESBL producing GNR are usually treated with:ESBL producing GNR are usually treated with:
– Carbapenemases – Meropenem, & Imipenem mostCarbapenemases – Meropenem, & Imipenem most
commoncommon

61. Carbapenamase Resistance (CRE)
• Resistance enzymes conferring resistance to
carbapenamase antibiotics (meropenem and
imipenem)
• Most common in Klebsiella pneumoniae –
where this enzyme is known as “KPC”
• Cross resistance to virtually all classes of
antibiotics – so very difficult to treat
• Treatment: Colistin or antibiotic combinations

62. Salmonella species
• Salmonella spp.
– Diarrhea with +/- fever – polys in the stool
– Infection from food - Eggs, meats and contaminated
uncooked vegetables, must ingest large #’s of organisms to
make you ill (1,00,000 bacteria), stomach acid protective
– Does not ferment lactose/ produces Hydrogen sulfide
– Selective agars for growth: SS and Hektoen
– Identification based on biochemical reactions & serologic
typing
– Kaufman White serologic typing scheme
• O Somatic (cell wall) antigen – Salmonella group “B”
• H flagellar antigens – 2 phases [h1 & h2] aids in speciation
Salmonella
• Vi capsular antigen – Found in S. typhi only

63. Salmonella Shigella
Agar (SS agar)
Salmonella and Shigella are
colorless due to lactose not
being fermented
Hektoen agar –
Salmonella produces H2S [Hydrogen
sulfide] producing black colonies
Shigella – green colonies
Normal flora – orange colored due to
fermentation of lactose

64. Salmonella typhi
• Typhoid fever – fever, sepsis, high fatality rate
• Vi capsular antigen surrounds the D cell wall antigen
• Boil solution of organism for 15 minutes to destroy the
Vi capsular antigen and expose the cell wall D antigen
• Serotyping can then be performed for the D antigen
• Moustache of H2S in the TSI tube
– Carrier state in gallbladder
– Ingest organism, it clears the bowel
then in @ 1 week enters
Blood stream & Bone Marrow

65. Shigella
• Diarrhea, +/-vomiting, fluid loss, polys and blood in stool ,
tenesmus, usually treated, Quinolone therapy
• Human to human transmission /control with good hygeine
• Low #’s of organisms to make you ill [10 – 100 bacteria]
• Non motile and No H2S produced (differ from
Salmonella) – Green colonies on Hektoen
• Does not ferment lactose
• 4 species based on somatic antigen
– S. boydii Group C
– S. dysenteriae Group A
– S. flexneri Group B
– S. sonnei Group D

66. Yersinia enterocolitica
• Diarrhea
• Major reservoir – swine
• Human usually infected by non pasteurized milk
• Causes septicemia in iron overload syndromes
• Unique infection Mesenteric adenitis – RLQ pain
which mimics appendicitis
• Grows well at 4 °C (like Listeria)
• CIN agar (Cefsulodin-irgasan-novobiocin) is
selective for Y. enterocolitica
• Has been associated banked blood infections related
to transfusion of infected products

67. Yersinia pestis - Plague
• Category A agent of bioterrorism
• Obligate flea/ rodent/ flea cycle
• Infected Flea bite - leads to Bubonic form/
painful buboes (lymph node swelling)
• Pneumonic form +/- bacteremia spread
• Fatality >=50%
• Endemic Southwestern USA
• Grows on blood agar
– catalase +, oxidase -
– Bipolar staining “safety pin”

68. Glucose Fermenters
Oxidase Positive
• Vibrio cholerae
– Rice water stool/ mucus flecks in diarrhea
– Natural environment is saltwater
– Virulence due to enterotoxin – receptor on epithelial cell –
activates adenyl cyclase – increases cAMP with
hyper secretion of NaCl and H20 – death from dehydration
and metabolic acidosis
– Halophilic bacteria which means it is a salt loving / 1% salt
actually enhances growth
– Curved appearance to gram negative rod
– Selective media – TCBS = thio citrate bile sucrose agar,
colony turns yellow due to sucrose fermentation
TCBS Agar

69. Other Vibrio species
• Vibrio parahaemolyticus
• Colony on TCBS medium is green = sucrose negative
• Diarrhea from ingestion of raw fish and shellfish
• Vibrio vulnificus
• Highly virulent Vibrio species – infection leads to formation of
painful skin lesions on lower extremities with muscle necrosis
• Most prevalent in patients with pre existing liver disease
• 50% fatality rate
• Ingestion of raw oysters and shellfish
from coastal waters
• Usuallly Green colonies TCBS

70. Classic Gram Negative Rod Gram
Stains
Campylobacte
r
Vibrio species
Enteric gram negative rod
Sea gull wings C shaped
Plumb and rectangular

71. Do not ferment Glucose
Oxidase negative
• Acinetobacter species – isolated from a hospital environment
and human skin, large gram negative cocco-bacilli
– Ac. baumannii is a major nosocomial pathogen
• Glucose oxidizer
• Acquires antibiotic resistance with pressure
– Ac. lwoffi –
• glucose non oxidizer
• Stenotrophomonas maltophilia
– Rapid maltose oxidizer
– Long Gram negative bacillus
– Naturally resistant to many antibiotics
– Gun metal gray pigment
– Nosocomial pathogen – super-colonizer when on long term Imipenem
therapy due to natural resistance to Imipenem

72. Glucose non-fermenter
Oxidase Positive
Pseudomonas aeruginosa
• Fluorescent & blue-green
pigment(pyocyanin)
• Grape-like odor
• Growth at 42˚C
– Ps fluorescens/putida – no growth at 42°C
• Major pathogen in cystic fibrosis
– Mucoid strains [polysaccharide capsule]
– in combination with Burkholderia cepacia
– can cause major lung damage
• Nosocomial pathogen –
associated with water & moisture
• Intrinsically resistant to many antibiotics

73. Glucose Non Fermenters/oxidase +
• Burkholderia cepacia
– Dry , yellow colony
– Oxidase negative
– Problem organism in cystic fibrosis
colonization and infection with extensive lung damage
• Flavobacterium (Chryseobacterium) meningosepticum
– Associated with fatal septicemia in the neonate
– Low virulence
– Environmental source
– Yellow pigment

74. Haemophilus species
Haemophilus influenza
– Variety of infections
– Transmission – close contact secretions
– Polysaccharide “B” capsule = virluence factor
– Requires 2 nutritional factors for growth
• X = hemin
• V= NAD (nicotinamide adenine dinucleotide)
• Demonstrate by satellite phenomenon or X/V strips
– Small pleomorphic GNR / Grows on chocolate agar
– Will not grow on 5% sheep’s blood agar
– Requires high level C0₂ [5 – 8%] for growth
– Vaccine targets the H. influenza type B
– Resistance to Ampicillin by beta lactamase production [15-
20 %], Cefotaxime becomes the antibiotic of choice
+

75. Disk test for Beta lactamaseDisk test for Beta lactamase
DetectionDetection
• Add bacteria to filter paper impregnated with Nitrocefin orAdd bacteria to filter paper impregnated with Nitrocefin or
Cefinase test (yellow colored/chromogenic cephalosporin)Cefinase test (yellow colored/chromogenic cephalosporin)
• Incubate at room temp for @ 1 minuteIncubate at room temp for @ 1 minute
• Positive result is color change fromPositive result is color change from yellow to redyellow to red - beta- beta
lactamase enzyme breaks down beta lactam ring to formlactamase enzyme breaks down beta lactam ring to form
hydrolyzed red end producthydrolyzed red end product
• Detects resistance to Amp/Pen/Cephalosporin inDetects resistance to Amp/Pen/Cephalosporin in
Haemophilus species, N. gonorrhoea , Moraxella catarrhalis,Haemophilus species, N. gonorrhoea , Moraxella catarrhalis,
and anaerobic gram negative rodsand anaerobic gram negative rods
• Does NOT detect the ESBL enzymeDoes NOT detect the ESBL enzyme

76. More Haemophilus species
• H. parainfluenza –
– requires V (NAD) factor only
– Usually normal flora in the upper respiratory tract
– One of the HACEK organisms of endocarditis
• H. (Aggregatibacter) aphrophilus – (new taxonomy)
– No factor requirements for growth
– Infections: abscesses (liver, lung, brain) & endocarditis
• H. ducreyi –
– Requires X factor
– Cause of Chancroid - venereal disease
– “school of fish” appearance on stains

77. Satellite phenomena
Demonstrates need for X and V factor
Small pleomorphic GNR

78. The HACEK group
• Oral flora can be pathogens of endocarditis caused
by poor detention or dental procedures
• Requires 2-4 days to grow in patient blood cultures
• Haemophilus species = oxidase neg, catalase neg
• Actinobacillus actinomycetom-comitans = oxidase
neg, catalase pos
• Cardiobacterium hominis = oxidase pos
• Eikinella corrodens = oxidase pos, colony pits BAP
• Kingella kingii = oxidase pos, hemolytic on BAP, also
cause infections in small children (septic joints)

79. Bordetella pertussis
Whooping cough – three stages of disease
– (1) Prodromal – flu like disease – most contagious stage
– (2) Catarrhal - cough - with classic whoop in small children
Toxin adheres to bronchial epithelial cells and cough
continues until toxin wears off – can be months
– (3) Paroxysmal - recovery phase
• Gram stain = Tiny gram negative coccobacillus
• Inhabits Nasopharynx – specimen source
• PCR most sensitive and specific for diagnosis
• Charcoal containing media for transport and culture –
Regan Lowe Charcoal agar
• Reservoir for infection – young adults due to waning
immunity. Reason behind booster shots for young adults

80. Pasteurella multocida
• Primary cause of Cat and Dog bite wound infections
• Human pneumonia from close animal contact
– Infections can disseminate to blood stream
• Found as normal flora in animal’s mouth
• Small gram negative coccobacilli
• Growth on 5% Sheep’s blood agar
– Non hemolytic grey colony
• Will not grow MacConkey agar (big clue)
• Oxidase Positive
• One of very few Gram negative rods
sensitive to penicillin

81. Capnocytophaga
• Fusiform shaped gram negative rods –
very pleomorphic
• Gliding motility, fingerlike projections from colonies
• Oxidase negative, Catalase negative
• C. canimorsus – dog bites with bacteremia – high% of these
infections lead to endocarditis
• Other Capnocytophaga species are normal flora in the human
mouth and
• Can infect mouth ulcers induced by chemotherapy –
• Blood stream can be invaded from infected mouth ulcer

82. Brucella species
• Disease – Fever of unknown origin, significant joint pain
• Small gram negative coccobacilli – slow and difficult to grow from blood
cultures – intracellular pathogen of the RES system
– Castaneda biphasic blood culture held for 21 days [old school]
– Current: Automated Blood culture systems with growth within 5 days
• Specimens: blood and bone marrow most profitable
– Granuloma formation in bone marrow
• Serology can be used for genera/species diagnosis
• Brucella species in clinical specimen related to animal
species the patient was exposed:
– B. abortus – ingestion of raw cow milk
– B. melitensis – ingestion raw goat milk, feta cheese
– B. suis – contact with pigs B. canis - contact with dogs
Granuloma in bone
marrow

83. Campylobacter
• Small curved bacilli –
shaped like sea gull wings
• C. jejuni – agent of diarrhea
– Related to undercooked poultry ingestion
– Requires selective media containing antibiotics -Skirrow’s blood agar
– Thrives at 42˚C - can use to selectively culture Campylobacter
– Requires microaerophilic atmosphere (high CO₂, low O₂)
– Significant % Guillain-Barre syndrome as sequelae of infection
• C fetus – Bacteremia in the immune suppressed host / does
not cause diarrheal disease
• C. jejuni – grows at 37˚C and 42˚, hippurate positive
• C. fetus - grows at 37˚C and 25˚C hippurate negative

84. • Reservoir – rabbits, rodents, ticks and flies. Humans infected
by bug bites or directly from exposure to animal blood
• Strongly associated with skinning rabbits with bare hands
• Bacteria can penetrate small breaks in skin:
– cause painful skin lesions –
– enlarged lymph nodes –
– leading to bacteremia (ulceroglandular tularemia)
– Pneumonia
• Great hazard to lab workers
• Fastidious small gram negative cocco-bacillus
• Culture media requires cysteine*
Francisella tularensis

85. Helicobacter pylori
• Small curved Gram negative bacilli
• Cause of acute gastritis…..gastric adenocarcinoma
• Human to human transmission/ fecal oral route
• H. Pylori, Rapidly!! And strongly urease positive – used for
detection directly from gastric biopsy tissue
• Difficult to grow in culture
• Stool antigen/diagnosis and test of cure ]
Serum antibody for exposure
• Treatment – Antibiotics and acid
suppression
Histologic exam of gastric
biopsy
Hematoxylin-eosin stain or
Warthin-Starry Silver stain

86. Legionella
Legionella pneumophila most common species [6 serotypes]
• Requires cysteine in culture medium for growth
• Buffered Charcoal Yeast Extract agar -colonies form in 3-5
days
• Will not show on Gram stain of specimens
• Use silver impregnation stains in tissue
• Pulmonary disease associated with water,
cooling towers, shower heads, stagnant water
• Urinary antigen test will detect L. pneumophila type I
infection only
• Treatment: Erythromycin (macrolide)
BCYE

87. Bacteria without cell walls
• Mycoplasma and Ureaplasma – have cell membranes only! Media and
transport contain sterols to protect the membrane
• Do not form discreet colonies on agar plates – must read plates under a
microscope to visualize organisms [up to 14 days of incubation]
• M. pneumoniae –
– community acquired pneumonia
– Serology and PCR for diagnosis
– Cold agglutinins produced
• Genital mycoplasmas
– M. hominis – fried egg colony, vaginitis, cervicitis, postpartum sepsis,
neonatal infections , pre rupture of membranes
– Ureaplasma urealyticum – rapid urea hydrolysis in broth, NGU &
upper genital tract infection, spontaneous abortion, neonatal
infections
Ureaplasma
Mycoplasma hominis

88. Difficult to grow
• Bartonella henselae – Diagnose by PCR and/or serology
– Cat scratch disease – exposure to cat and cat excrement
– Bacillary angiomatosis – vascular skin lesion +/- invasion / HIV
• Bartonella quintana – cause of trench fever/ vector is the
body louse/Diagnose by Serology
• Chlamydia trachomatis Serovars L1,L2,& L3
agent of Lymphogranuloma venereum
– Serology / clinical findings – lymphatics and lymph nodes involved
• C. pneumoniae (TWAR agent)- Pneumonia, Diagnose by PCR
• C. psittaci- psittacosis, pneumonia, exotic parrot exposure/
Serology, PCR and epidemiology

89. Molecular Testing for Neisseria gonorrhoeaeMolecular Testing for Neisseria gonorrhoeae
and Chlamydia trachomatisand Chlamydia trachomatis
• Amplification of DNA by Polymerase Chain Reaction (PCR)Amplification of DNA by Polymerase Chain Reaction (PCR)
– Urine, Cervix, and urethral most often testedUrine, Cervix, and urethral most often tested
– More sensitive than any culture based systemMore sensitive than any culture based system
• Sensitivity/Specificity @ 96%/99%Sensitivity/Specificity @ 96%/99%
• Females most sensitive specimen = cervixFemales most sensitive specimen = cervix
• Males good sensitivity with urine and urethralMales good sensitivity with urine and urethral
• PCR replaced culture methods as “Gold” standard ofPCR replaced culture methods as “Gold” standard of
detectiondetection
Iodine staining
of inclusions in McCoy
Cell culture
Elementary bodies in
Fluorescent antibody stain

90. More difficult to grow
• Ehrlichiosis – Rickettsia bacteria
– Zoonotic intracellular pathogens
– Anaplasma spp, inclusion in the PMN
– Ehrlichia spp inclusion in the Monocytes
– Vector = Ixodes tick
– Fever, leukopenia, thrombocytopenia,
– Elevated serum aminotransferases,
– No rash (differs Rocky Mountain Spotted Fever)
• Found in the south central, southeast , midwest USA
• PCR and serology for diagnosis

91. Spirochetes
• Borrelia burgdorferi - Lyme’s disease
– Primarily found in NE part of USA
– Vector = Ixodes tick
– Serology and PCR
• Borrelia recurrentis - Relapsing fever
Vector = human body louse
Blood smear observe spirochete

92. Spirochetes
• Treponema pallidum
– Syphilis
– RPR and VDRL for antibody detection
– Molecular methods
• Brachyspira – intestinal spirochete found
on the brush border of the intestine,
?? Role in disease
• Leptospira interrogans – Leptospirosis
– Fever with rash and renal involvement
– Urine from rats and other animals contaminate water supplies
Darkfield from chancre lesion
Spirochete – Shepherd’s crook

93. Unusual Bacterial diseases
• Granuloma inguinale
– Klebsiella (Calymmatobacterium) granulomatis
– Rare STD – causes ulcerative genital lesions
• Streptobacillus moniliformis
– Rat bite fever or Haverhill fever
– L form - cell wall deficient bacteria
– Inhibited by SPS in blood culture media
– Needs serum supplementation to grow, will not grow on
routine bacteriology media
– Infection obtained from rat bite

94. Anaerobes
• Anaerobic infections can occur in virtually
every organ and region of the body
• Polymicrobial – both aerobic and anaerobic species in the
infections
• Endogenous organisms (commensal flora) cause most
anaerobic infections
– Due to trauma, vascular or tissue necrosis cutting off the oxygen
supply to the involved tissue
• Surgery plus antibiotics often necessary
• Anaerobic culture collection – must be oxygen free
– Gel containing swabs
– ESwab,
– Evacuated vials (port o cult)/ oxygen free collection
– Do not refrigerate specimens – absorb oxygen and kill anaerobes

95. Anaerobes
• PRAS media – pre reduced anaerobically sterile
– Media packaged in oxygen free environment
• Most common media used
– CDC anaerobic blood agar
– Kanamycin-vancomycin blood agar
– Bile Esculin agar
– Thioglycollate broth
– Chopped meat glucose broth
• Anaerobic gas pack jars – incubate cultures in anaerobic conditions
• Wet pack – add 10 ml water to hydrogen and CO2 generating
envelope/ requires palladium coated catalysts – generate heat
• Dry pack – (Anaeropack) Absorbs O2 and generates CO2
• Anaerobic bacteria can be poorly staining with bizarre & irregularly shape

96. Anaerobic Gram Negative Rods

97. Bacteroides fragilis group
Pleomorphic irregular staining gram negative rod
–Grows in the presence of bile
–Esculin positive – turning media black
–Resistant to Penicillin and Kanamycin
–Common normal flora in GI tract
–Infections foul smelling/gas produced
–B. fragilis* - most common
–B. ovatus
–B. thetaiotamicron – indole positive
–B. uniformis B. vulgatus
• Resistant to Penicillin by beta lactamase enzyme
• Metronidazole is one antibiotic of choice
Growth on bile
Black pigment

98. Gram Negative Anaerobic Bacillus
• Prevotella and Porphyromonas species
– Will not grow in the presence of bile
– Will not turn black on esculin media
– Brick red fluorescence and black pigment
– Normal commensal flora of the upper respiratory tract
– Respiratory tract infections

99. Fusobacterium spp.
Long thin gram negative bacilli –
spindle shaped with pointed ends
• Normal flora in upper respiratory tract
• Associated with mouth and respiratory tract abscess
formation and liver abscess
• Vincent’s angina – necrotizing oral infection caused
by Fusobacterium species and spirochetes
• Lemierre’s syndrome - oropharyngeal infection that
leads to thrombosis in jugular vein, septicemia, high
fatality rate, caused by Fusobacterium necrophorum

100. Anaerobic Gram Positive Rods

101. Clostridium species
• Gram positive bacilli (boxcar shaped ) with spores
– Bacilli may over-decolorize and appear red
• Clostridium perfringens
– Predominate anaerobic G+R in intestine
– Double zone of beta hemolysis on BAP
– Lecithinase produced on egg yolk agar
– Reverse camp test positive
Lecithinase
Reverse Camp Test

102. Clostridium
• Clostridium botulinum –
– Adult disease – Preformed heat labile toxin
ingested in mass produced or home-canned foods
– Infant disease - spore ingested from product
produced in nature, neurotoxin produced in gut
• Begins with constipation and difficult sucking bottle
• Associated with Honey, soil, household dust
– Life threatening neuroparalytic disease
• Clostridium tetani
– Tetanus
– Gram stained cells appear like Tennis racket
– Toxin enters human due to penetrating skin injury
– Disease occurs in Non-immunized
– Spastic contractions of voluntary muscles, hyper-reflexia, lock jaw
(trismus)

103. Clostridium
• C. septicum –
– Bacteremia or Gas Gangrene in patient with underlying
malignancy
• C. difficile –
– Normal Colonization in 5% adults and 70% healthy infants
– Disease = Antibiotic associated colitis,
pseudomembranous colitis due to toxin production
[Virulence Factor]
• Toxin A – enterotoxin causing fluid accumulation
• Toxin B – potent cell cytotoxin
• Binary toxin (Nap1) strain is unique and produces larger amount of
toxins A and B and is more virulence
– Diagnosis of infection:
• EIA methods [toxin A/B] are not sensitive and are discouraged
• PCR methods [toxin B] are more sensitive and for infection
• Culture – Cycloserine, Cefoxitin, Fructose Agar [CCFA]

104. Actinomyces
• Branching gram positive bacilli - do not form spores
• Normal flora in the mouth
• Capable of forming sulfur granules
in tissue – often found on normal tonsil
• Actinomyces israelii – associated with oral, thoracic,
and abdominal infections, IUD infections
B

105. Branching Gram positive rods
of Actinomyces – antler like
Molar tooth colony
Sulfur granule

106. Propionibacterium acnes
• Pleomorphic gram positive rod
• Catalase positive
• Indole positive
• Normal flora - skin, oral, GU and GI
• Potential contaminate in blood cultures
• Pathogen in cerebral shunt infections
• Firmly established as significant cause of prosthetic joint
infection – particularly shoulder joints
• Cultures should be held up to 7- 14 days
• Therapy - Ampicillin

107. Bacterial vaginosis
• Clue cells are diagnostic
• Mixed anaerobic/aerobic bacterial infection - the two most common
organisms in vaginosis are:
– Gardnerella vaginalis (aerobic gram variable rod) and Mobiluncus
(anaerobic curved gram negative rod)
– Human blood agar used to culture Gardnerella, it
is beta hemolytic and distinctive morphology
• Nugent score – gram stain scoring system to diagnose
bacterial vaginosis [BV]
– Healthy = Lactobacillus-like Gram positive rods
– Intermediate = mixed bacterial types
– BV = Gardnerella and Mobiluncus on smear
Clue Cell