Gram-positive cocci include Staphylococcus (catalase-positive), which grows clusters, and Streptococcus (catalase-negative), which grows in chains. The staphylococci further subdivide into coagulase-positive (S. aureus) and coagulase-negative (S. epidermidis and S. saprophyticus) species. Streptococcus bacteria subdivide into Strep. pyogenes (Group A), Strep. agalactiae (Group B), enterococci (Group D), Strep viridans, and Strep pneumonia. Gram-positive bacilli (rods) subdivide according to their ability to produce spores. Bacillus and Clostridia are spore-forming rods while Listeria and Corynebacterium are not. Spore-forming rods that produce spores can survive in environments for many years. Also, the branching filament rods encompass Nocardia and actinomyces. Gram-positive organisms have a thicker peptidoglycan cell wall compared with gram-negative bacteria. It is a 20 to 80 nm thick polymer while the peptidoglycan layer of the gram-negative cell wall is 2 to 3 nm thick and covered with an outer lipid bilayer membrane. Bloodstream infection mortality rates have increased by 78% in just two decades[1]. Gram-positive organisms have highly variable growth and resistance patterns. The SCOPE project (Surveillance and Control of Pathogens of Epidemiologic Importance) found that gram-positive organisms in those with an underlying malignancy accounted for 62% of all bloodstream infections in 1995 and 76% in 2000 while gram-negative organisms accounted for 22% and 14% of infections for these years.[2]

1. • Gram reaction classification
• Gram positive cocci
• Gram positive rods
• Gram negative cocci
• Gram negative coccobacilli
• Gram negative rods
• Oxidase negative
• Oxidase positive
• Mycobacterium
• Miscellaneous bacteria
Bacillus
Clostridium
Listeria
Corynebacteria
Neisseria
Moraxella
Haemophilus
Brucella
Bordetella
Enterobacteriac
eae
The Pseudomonas
Vibrio species
Campylobacter
Helicobacter
M.tuberculosi
s complex
M. leprae
Staphylococci
Streptococci
Enterococci

2. PATHOGENIC GRAM POSITIVE
COCCI

3. There are two most important genera of gram-positive
cocci
• The Genus Staphylococcus
• The Genus Streptococcus
A. The Genus staphylococcus
• Staphylococci make a very large contribution to man's
Commensal flora and also account for a high
proportion of acute and chronic suppurative lesions.

4. General properties /characteristics
– Gram-positive cocci arranged in Grape like clusters
– Non Motile, non spore forming
– Produce catalase
The genus:
– Has around 49 Species
– Contain 3 main Species of Clinical importance:
• S. aureus
• S. epidermis, S. saprophyticus
• S. haemolyticus,
Staphylococcus lugdunensis

5. Fig . Virulence determinants of Staphylococcus aureus

6. Pathogenesis:
• Pathogenesis of S. aureus is combined effect of:
• Extra cellular factors
• Toxins
• Invasive properties of the strain
• S. aureus causes suppurative and toxinoses in humans.
• It causes superficial skin lesions, pneumonia, deep-seated
infections, food poisoning

8. B. Toxin-mediated staphylococcal diseases
1. Food poisoning
• Results from ingestion of preformed enterotoxin in contaminated
food that is improperly cooked and kept unrefrigerated for some
time.
• Source of contamination of food: the hands or nose of a
cook/food handlers/carriers.
• Types of food involved in staphylococcal food poisoning are
carbohydrate rich foods, e.g. cakes, pastry, milk, etc.
• IP: short (1-8 hrs) followed by nausea, vomiting, diarrhoea
and general malaise with no fever.

9. 2. Toxic shock syndrome (TSS):
– This is associated with TSST-1, first described in
menstruating women using tampons.
– The syndrome also occurs with wound or localized
infections.
– TSS has an abrupt onset of fever, vomiting,
diarrhoea, muscle pains, rash
– Hypotension, heart and renal failure may occur in
severe cases.

10. 3. Staphylococcal scalded skin syndrome (SSSS):
– Occurs due to the exfoliative toxin produced by phage
II strains of S. aureus.
– The syndrome occurs in babies and young children.
– It is characterized by large areas of desquamation of the
skin and generalized bullae formation.

12. Lab. Diagnosis
Potential specimens:
⚫ Pus, Tracheal aspirates, Blood, CSF
Laboratory Diagnosis:
⚫Microscopy: gram-positive cocci in grape – like cluster
⚫Culture: produce beta-hemolytic colonies on blood agar
⚫ Biochemically: Coagulase and catalase test – positive
⚫Identification of an isolate as a staphylococcus relies largely on
microscopic and colony morphology, and catalase positivity.
⚫Treatment: Penicillin, methicillin, vancomycin

13. Properties
• Gram positive in reaction
• Forms pairs / chains during growth
• Ubiquitous
• Contain normal flora & pathogenic Spp.
• Produce extra cellular substances & enzymes
13
GENUS STREPTOCOCCI

14. • Heterogeneous group of bacteria
– No system suffice to classify
– Spp characterized by:
• Colony characteristics
• Hemolysis (alpha/ beta) patterns on blood agar
• Antigenic composition of group specific cell wall
subs.
• Biochemical reactions
14

15. Classification of Strep. cocci
Based on:
1. Colony morphology & hemolytic rxns on blood agar
– Alpha, beta - hemolysis or gamma - hemolysis
2. Serologic specificity of the cell wall grp specific carbohydrate
– Lance field classification (21 in number)
3. Capsular antigens: S. pneumoniae into 84 types
15

16. 4. Battery of Biochemical Tests:
• Sugar fermentation rxns
• Tests for the presence of enzymes
• Tests for susceptibility / resistance to certain ABCs
N.B: Biochemical tests are used for Spp that do not react with
the commonly used antibody preparations for the Grp.
specific subs.
5. Resistance to physical & chemical factors
6. Ecologic features
7. Molecular techniques (Gene amplification & Sequencing)
16

17. • Gram+ ve cocci usually in chain
• Some strains produce capsule and pathogenic strain contain
M protein (attachment factor, antigenic and anti-phagocytic)
– The most pathogenic member of the genus
– Produces a large number of powerful enzymes and
toxins.
– Present as a commensal in the nasopharynx of healthy
adults, and more commonly in children (10% carriage)
Group A beta -Hemolytic Streptococci
(Streptococcus pyogens)

19. Transmission
– Person to person from droplets during coughing,
on the hand of health personnel, or from fomites
like towels as well by vectors during insect bite.

20. Pathogenesis:
• Causes disease by three main mechanisms:
1. Inflammation
• Tonsillitis, pharyngitis, cellulites, otitis media, Impetigo,
Erysipelas, etc
• The enzymes contribute for the invasiveness includes:
– Hyaluronidase- spreading factor
– Streptokinase- dissolves fibrin in clots.
– Dnase- Depolymerizes DNA in exudates or necrotic
tissue

21. Suppurative disease
• Pharyngitis: Reddened pharynx with exudates generally
present; cervical lymphadenopathy can be prominent
• Scarlet fever: Diffuse erythematous rash beginning on
the chest and spreading to the extremities; complication
of streptococcal pharyngitis
• Pyoderma: Localized skin infection with vesicles
progressing to pustules; no evidence of systemic disease
21

22. • Erysipelas: Localized skin infection with pain,
inflammation, lymph node enlargement and systemic
symptoms
• Cellulitis: Infection of the skin that involves the
subcutaneous tissues
• Necrotizing fasciitis: Deep infection of skin that involves
destruction of muscle and fat layers (FLESH EATING
BACTERIA)
22

23. Flesh eating bacteria

24. 3. Immunogenic disorder
• Is due to the inflammation caused by immunologic response
to streptococcal M proteins that cross – react with human
tissue
a) Rheumatic fever: is due to cross-reaction between antibody
& human heart & joint tissue; occurs after 2 weeks of
pharyngitis
b) Acute glomerulonephritis (AGN): caused by immune
complexes bound to glomeruli; occurs 2 – 3 weeks skin or
respiratory infection.

25. Laboratory diagnosis
Specimen- throat swab, pus, blood
Gram’s rxn - gram positive cocci in chains
Culture- grow in aerobic and anaerobic environment at
temp 35- 37%
– Grow in ordinary media with shiny or dry colonies with
gray white or colorless appearance
– Don’t grow in MacConkey agar
– Shows clear zone of hemolysis on blood Agar

28. ▪ Biochemical Test and Sensitivity Test
▪ Catalase –Negative
▪ Litmus milk reduction test –Negative
▪ Bile solubility test –Negative
▪ CAMP test –Negative
▪ Bacitracin –Sensitive
• Antigen Detection test
ELISA and agglutination test (75-80% sensitive)
• Serological Diagnosis
- By latex agglutination (ASO)

29. Treatment :-
• S. pyogenes strains are susceptible to penicillin.
• Erythromycin is usually used to treat patients hypersensitive
to penicillin but resistance to erythromycin (and also to
tetracyclines) is being increasingly reported.

30. B. Group B beta-Hemolytic Streptococci (Streptococcus
agalactiae)
– S. agalactiae is found in the vaginocervical tract of
female carriers, and the urethral mucous membranes
of male carriers, as well as in the GI tract.
– Transmission occurs from an infected mother to her infant at
birth, and venereally (propagated by sexual contact) among
adults.
– Group B streptococci are a leading cause of pneumonia,
meningitis and septicemia in neonates, with a high mortality
rate.

31. Laboratory diagnosis
• Specimens: cerebrospinal fluid, ear swab and
blood for culture from neonates.
• High vaginal swab is required from women with
suspected sepsis.

32. Technique
1. Microscopy
• Group B streptococci are Gram positive cocci, occurring
characteristically in short chains but also in pairs and
singly.
• The organisms are non-motile. Most strains are capsulated.
2. Culture
• Blood agar: Most strains of S. agalactiae produce grey mucoid
colonies about 2 mm in diameter, surrounded by a small zone of beta
hemolysis with large colony.

33. C. Groups C & G
• Occur in nasopharynx
• Cause sinusitis, bacteremia, or endocarditis
• ß – hemolytic on blood agar
• Identified by rxns with specific antisera for Grps
C & G

34. D. Enterococcus species
• E. faecalis (formerly classified Streptococcus faecalis) is the
main pathogen in the genus Enterococcus, causing about
95% of enterococcal infections including infections of the
urinary tract, biliary tract, ulcers (e.g. bed sores), wounds
(particularly abdominal) and occasionally endocarditis or meningitis.
• It is a normal commensal of the vagina and intestinal tract.
• A minority of infections are caused by E. faecium.

35. LABORATORY FEATURES
Morphology
• Enterococcus species are Gram positive cocci, occurring in
pairs or short chains.
• They are non-capsulate and the majority are non-motile.

36. Culture
• Enterococci are aerobic organisms capable of growing over
a wide temperature range, 10–45 ºC.
• Blood agar: Enterococci are mainly non haemolytic but
some strains show alpha or beta-haemolysis.
• MacConkey and CLED agar: E. faecalis ferments lactose,
producing small dark-red magenta colonies on MacConkey
agar and small yellow colonies on CLED (cysteine lactose
electrolyte-deficient) agar.

37. Streptococcus Pneumoniae (Pneumococcus)
• S. pneumoniae are gram-positive, non motile, encapsulated
cocci.
• They are lancet-shaped, and their tendency to occur in pairs
accounts for their earlier designation as Diplococcus
pneumoniae.
• In tissue, pus or sputum pneumococci are typically arranged
in pairs (diplococci) each coccus some what elongated and
pointed at one end but rounded at the other (lanceolate).
– They are surrounded by a polysaccharide capsule.

38. Pathogenicity
• S. pneumoniae causes lobar pneumonia, bronchitis (often
with H. influenzae), meningitis, bacteraemia, otitis media,
sinusitis and conjunctivitis.
• Severe infections can occur in the elderly and those already
in poor health or immunosuppressed.
• Risk of infection is increased following splenectomy.
• In tropical and developing countries, S. pneumoniae is a
major pathogen, responsible for acute life-threatening
pneumonia and bacteraemia in those co-infected with HIV.

39. ⮚Direct detection of pneumococcal antigen in body
fluid
• Rapid latex and coagglutination tests are available to
detect capsular pneumococcal antigen in CSF, pleural
fluid, serum and urine.
Treatment and prevention
• Antibiotics with activity against pneumococci include
– penicillin,
– erythromycin,
– co-trimoxazole.
N.B. Penicillin- resistant strains are becoming an
increasing problem in tropical Africa, South Africa,
and elsewhere.
Polyvalent vaccine for prevention of certain strains.