Gram positive bacteria

1. STREPTOCOCCI

3. 3

4. 4

5. 5
Structure
Streptococci are Gram-positive,
Non motile, Non spore forming,
Catalase-negative cocci that occur in pairs
or chains

6. 6
Catalase test
• Add hydrogen peroxide to culture material

7. 7
Classification of Streptococci based on :
 Hemolysis on blood agar
They are divided into three groups by the type of :
 beta-hemolytic (clear, complete lysis of red cells).
 alpha hemolytic (incomplete, green hemolysis),
 gamma hemolytic (no hemolysis).
Serologic grouping is based on antigenic
differences in cell wall carbohydrates (Lancfield
group Streptococcus A to V), in cell wall pili-
associated protein, and in the polysaccharide capsule
in group B streptococci.

8. Classification of Streptococci
• Strep: gram positive, catalase negative
–Nutritionally fastidious
–Facultative anaerobes but don’t use
oxygen metabolically (create lactic
acid)
• Initial classification based on hemolysis
on sheep blood agar plates
–α (partial, reduction), β (complete),
and γ (none)

9. Hemolysis
• β-hemolysis
– Red blood cells (RBCs) are completely lysed, resulting
in a clear area around the colony.
• Α-hemolysis
– RBCs are partially lysed, resulting in a greening of the
area around the colony.
• α’ Hemolysis has intact zone of RBCs with hemolysis around
them
• γ-hemolysis (nonhemolytic)
– RBCs are not lysed, so there is no change in agar color.
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10. 10
hemolysis reaction - sheep blood agar
• α (alpha)
– partial hemolysis
– green color
• β (beta)
– complete clearing
• γ (gamma)
- no lysis
White colonies

11. Hemolysis Patterns of Streptococci

12. Types of Hemolysis (Cont.)
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13. Hemolysis on Blood Agar
Hemolysis on BA
– -hemolysis
Partial hemolysis
Green discoloration around colonies
e.g. S. pneumoniae & S. viridans
– -hemolysis
Complete hemolysis
Clear zone of hemolysis around colonies
e.g. Lancefield Group A & B (S. pyogenes & S. agalactiae)
– -hemolysis
No hemolysis
e.g. Group D (Enterococcus sp.)
• Acute glomerulonephritis
• Scarlet fever

15. 15
Rebecca Craighill Lancefield (1895-1981)

16. Classification of Strep from Humans
Species Lancefield Hemolytic Comments
S. pyogenes A β
S. agalactiae B β Group B Strep
S. dysgalactiae
subsp. equisimilis
C, G β Formerly S. equisimilis;
pyogenic; respiratory, SSTI
S. pneumoniae None α
S. bovis species
group
D α, γ Viridans; associated with colon
cancer; IE
S. mutans group not useful α, γ, rarely β Viridans; dental caries and IE
S. salivarius group not useful α, γ Viridans; opportunistic
S. mitis group not useful α Viridans; IE, opportunistic
S. anginosus group A, C, F, G,
or no
detectable
α, β, γ Viridans; formerly known as S.
milleri; 3 species S. anginosus, S.
constellatus, and S. intermedius;
purulent infxns

17. Lancefield Groups
• Membrane Ag
• Groups A-H, K-V
– Group A
• Strep. pyogenes
– Group B
• Strep. agalactiae
– Group C, F, G
• Strep equisimilis
• Strep zooepidemicus
• Strep anguinosus
– Group D
• E. faecalis
• Strep bovis
• Strep equines
– Group K
• Strep salivarius
– Viridans
• Strep mutans
• Strep mitis
• Strep sanguis
– Pneumococci

18. MEDICAL IMPORTANT SPECIES
1. S.Pyogenes.
2. S.agalacticae
3. S.pneumoniae
4. S.Viridans
18

19. S. pyogenes (Group A) Virulence
Factors
• M protein
– Essential for virulence
– Resistance to infection is related to M protein
antibody production.
• Fibronectin- binding protein (Protein F)
• Lipoteichoic acid
– Mediate attachment to host cells
• Capsule prevents opsonized phagocytosis.
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20. S. pyogenes (Group A) Virulence
Factors (Cont.)
• Streptolysin O
– Responsible for hemolysis on blood agar plate
(BAP)
• Oxygen labile: only active under anaerobic conditions
– Destroys white blood cells (WBCs), platelets, RBCs,
and other tissues
• Streptolysin S
– Oxygen stable
• Can lyse RBCs and WBCs
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21. S. pyogenes (Group A) Virulence
Factors (Cont.)
• DNases A-D
– Help destroy foreign DNA by excreting it into
surrounding area
• Hyaluronidase (spreading factor)
– Breakdown of connective tissue
• Streptococcal pyrogenic exotoxins (SPEs)
– Formerly erythrogenic toxin
– Causes a red spreading rash
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22. Strep Virulence Factors

23. S. pyogenes (Group A) Clinical
Infections
• Pharyngitis
– Strep throat
• Scarlet fever
– Streptococcal pyrogenic exotoxins cause rash.
– Rash appears on the chest and spreads to the
trunk and limbs.
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24. Streptococcal Pharyngitis:

25. Scarlet Fever Pictures

26. S. pyogenes (Group A) Clinical
Infections (Cont.)
• Skin or pyodermal infections
• Through bites or abrasions to the skin
– Impetigo
• Usually in very young children
– Erysipelas
• Skin infection with a spreading red rash with a demarcated
but irregular edge
– Mostly elderly
– Cellulitis
• Deep invasion of GAS leading to necrosis and gangrene
• Sepsis
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27. 27
Erysipelas

28. 28
Impetigo

29. 29
Pyoderma

30. 30
Cellulitis

31. S. pyogenes (Group A) Clinical
Infections (Cont.)
• Necrotizing fasciitis
– Invasive infection characterized by a rapidly
progressing inflammation and necrosis of the skin,
subcutaneous fat, and fascia
• Described as “flesh-eating disease”
– Life-threatening infection
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32. Necrotizing Fascilitis (flesh eating
strept):
•

33. S. pyogenes (Group A) Clinical
Infections (Cont.)
• Streptococcal toxic shock syndrome
– Rare but results from the toxin associated with
scarlet fever
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34. Post-Streptococcal Sequelae
• Rheumatic fever
– Occurs after pharyngitis
– Inflammation of the joints, heart, blood vessels, and
subcutaneous tissues
– Can cause serious damage to the heart valves
• Acute glomerulonephritis (AGN)
– Can occur after pharyngitis or cutaneous infection
– Immunologic mechanisms lead to antigen antibody
complexes, resulting in damage to the kidneys
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35. Laboratory Diagnosis
• Specimen collection
– Swab rubbed over the posterior pharynx and each tonsillar
area
• If exudate is present, it should also be touched with the swab.
– Avoid contamination by tongue and uvula
– Recovery
• Sheep blood agar (SBA) plate is inoculated and streaked for isolation.
• Observe after 24 hours for the presence of β-hemolytic colonies
– If none, incubate for an additional 24 hours
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36. Laboratory Diagnosis (Cont.)
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 Key Tests
 Throat cultures: bacitracin, pyrrolidonyl
aminopeptidase (PYR), Lancefield typing
 Other specimens: hippurate hydrolysis, Christie
Atkins Munch-Petersen (CAMP) test, bile esculin
test, 6.5% sodium chloride (NaCl) broth

37. Strep pyogenes diseases summary
• Pharyngitis
• Scarlet Fever (rash)
• Skin
– Pyoderma
– Impetigo
– Erysipelas
– Cellulitis
• Strep TSS
• Necrotizing fasciitis
• Immune Mediated
– Rheumatic fever
– Glomerulonephritis

38. PATHOGENESIS
• Human are only reservoir.
• Transmission is through ,contact ,droplets,
food , fomites
• Port of entry is through skin or pharynx.
• Children are predominant group affected for
cutaneous and throat infections.
• Systemic infections and progressive diseases
may occur if untreated.
38

39. SIGNS AND SYMPTOMS
• Pharyngitis… > horse of muffled voice ,
difficult in swallowing.
• Pyoderma…. > redness of skin( resemble to
spider bites ),
• Acute rhematic fever …>tenderness in joints ,
fever.
• Acute glomerulonephritis …>. Tiredness , loss
of appetite , dry skin.
39

40. Streptococcus agalactiae (Group B
Streptococcus)
• Capsule is most significant virulence factor
• Colonizes genital and lower GI tracts of 10-
40% of women; also found in oropharynx,
upper GI
• Pass to baby during birth

41. Streptococcus agalactiae (Group B
Streptococcus)
Pathogenicity
 S. agalactiae (Lancefield Group B), it forms part
of the normal microbial flora of the female
genital tract.
 causes septic abortion and puerperal or
gynaecological sepsis, and occasionally urinary
tract infection.
 Occasionally it causes neonatal septicaemia and
meningitis (rare in most developing countries).

42. Streptococcus agalactiae (Group B
Streptococcus)
LABORATORY FEATURES
• Specimens: Include cerebrospinal fluid and
blood for culture from neonates.
• High vaginal swab is required from women
with suspected sepsis.

43. Laboratory Diagnosis
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 β-hemolysis  Bacitracin,
Hippurate
hydrolysis, and
CAMP test

44. S. agalactiae (Group B) Virulence
Factors
• Capsule: preventing phagocytosis
• Sialic acid appears to be important factor in
inhibiting alternative pathway of complement.
• Hemolysin
• DNases
• Hyaluronidase
• Protease
Treatment
– Ampicillin
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45. S. agalactiae
(Group B) Infections (Cont.)
• Detection of group B strep
– Collect vaginal and rectal material between 35 and
37 weeks gestation
– Inoculate to select broth,
– All positive women should be treated to reduce
the risk to infant.
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46. S.pneumonia
46

47. Cont..
• S.pneumoniae is a frequent colonizer of
human nasopharynx
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.
47

48. CDC Estimations
48

49. Pathogenesis
• S.pneumoniae is a normal member of the
respiratory tract flora invasion results in
pneumonia .The best virulence factor is
polysaccharide capsule which protect the
bacterium phagocytosis.
49

50. HOST DEFFENCE
• Protection against infection depends on a
normal mucocilary barrier and intact
phagocytic and T-independent immune
response type specific anti-capsule antibody is
protective
50

51. EPIDEMIOLOGY
• Pneumococcal pneumoniae is most common
elderly debilitated or immunosuppressed
individuals .
• The disease often sets in after a preceding
viral infection damages the respiratory ciliated
epithelium , incidence there fore peaks in the
winter.
51

52. Diseases
• Pneumonia
• Meningitis
• Sinusitis
• Otitis media
52

53. S.Pnemoniae Sinisitis disease
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54. Viridans Streptococci
• Normal flora of URT, female genital tract, and
gastrointestinal (GI) tract
• Many show α hemolysis
• Fastidious, with some requiring CO2
• Viridans streptococci have five groups
– S. mitis group
– S. mutans group
– S. salivarius group
– S. bovis group
– S. anginosus group
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55. Viridans Streptococci Clinical Infections
• Generally opportunistic pathogens
– Oropharyngeal commensals
• Most common cause of bacterial endocarditis
– More common in children than adults in patients with
hematologic malignancies
• Other diseases
– Tooth decay
• Most penicillin susceptible
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56. Enterococcus
• Part of Streptococcus until 1984.
• Can grow in 6.5% NaCl and from 10°-45°C;
hydrolyze esculin in presence of 40% bile salts
• Most infections from E. faecalis or E. faecium;
leading cause of nosocomial infxns
• Colonize GI tract; selected for by abx

57. Enterococcus: Clinical Manifestations
Epidemiology:
Found in intestinal tract , female genital tract
,less in oral cavity ( infrequent brushers)
Disease caused:
Infection in urinary tract
Septicemia
Ocassionally endocarditis or Meningitis