1. Streptococci and Other Streptococci-like Organisms

2. Case Study 9-year-old boy complains of fever and sore throat
On examination, his pharynx is red and his tonsils are swollen
His cervical lymph nodes are also swollen
A throat culture is taken

3. Points to Consider Clinical symptoms presented by the patient
The serious complications that may result from this type of infection
How to recover and identify the infecting organism
What other species are involved in clinical infections
Other points to consider

4. Streptococcus and Enterococcus: General Characteristics
Gram-positive, facultatively anaerobic cocci
Most are typically spherical; some may appear elongated

5. Streptococcus and Enterococcus: General Characteristics
Appear in chains when smears are prepared from broth cultures
Catalase-and oxidase-negative

6. Streptococcus and Enterococcus: Habitat and Clinical Infections
Indigenous respiratory tract microbial flora of animals and humans
Certain species are also found in the gastrointestinal and urogenital tracts of humans
Clinical infections
Upper and lower respiratory tract infections
Urinary tract infections
Wound infections
Endocarditis

7. Streptococcus and Enterococcus: Cell Wall Structure
Thick peptidoglycan layer
Teichoic acid
C=carbohydrate layer present except in viridans group
Capsule in S. pneumoniae and in young cultures of most species

8. Streptococcus and Enterococcus: General Characteristics
Hemolytic Patterns
Beta (ß) a clear, colorless zone around the colony caused by complete hemolysis of the red blood cells in the agar

9. Streptococcus and Enterococcus: Hemolytic Patterns
Alpha (a):hemolysis showing a greenish discoloration around the area surrounding the colony due to incomplete hemolysis of the red blood cells in the agar

10. Streptococcus and Enterococcus: Hemolytic Patterns
No hemolysis (gamma): colonies show no hemolysis or discoloration

11. Classification of Streptococcus and Enterococcus

12. Biochemical Identification
Susceptibility tests
Bacitracin (0.04 units) or “A” disk
Identifies Group A streptococci
Group A streptococcus is susceptible to “A” disk (left)

13. Biochemical Identification
Susceptibility test
Trimethoprim sulfamethoxazole (SXT)
Inhibits beta-hemolytic streptococcal groups other than A and B
Group A streptococcus growing in the presence of SXT

14. Biochemical Identification
Susceptibility test
Optochin “P” disk
Differentiates S. pneumoniae from other alpha-hemolytic streptococci (Viridans group)
Bile solubility test
S pneumoniae lyses in a suspension of sodium deoxycholate while other viridans streptococci do not lyse

15. Biochemical Identification
PYR hydrolysis
Substrate L-pyrrolidonyl-b-napthlyamide (PYR) is hydrolyzed by Group A Streptococci and Enterococcus sp.
As specific as 6.5% NaCl broth for Enterococcus sp.
More specific than Bacitracin for Group A streptococci
PYR test for Group A streptococci and enterococci. Both are positive for this test (right); left is a negative result

16. Biochemical Identification
Hydrolysis
Hippurate hydrolysis
Differentiates Group B streptococci from other beta hemolytic streptococci
Group B streptococci hydrolyzes sodium hippurate

17. Biochemical Identification
Christie-Atkins, Munch-Petersen (CAMP) test
Detects the production of enhanced hemolysis that occurs when b-lysin and the hemolysins of Group B streptococci come in contact
Group B streptococci showing the classical “arrow-shaped hemolysis near the staphylococcus streak

18. Biochemical Identification
Bile Esculin hydrolysis
Ability to grow in 40% bile and hydrolyze Esculin are features of streptococci that possess Group D antigen
Growth in 6.5% NaCl broth
Differentiates Group D streptococci from enterococci
Both Group D streptococci and enterococci produce a positive (left) bile Esculin hydrolysis test.

19. Clinically Significant Streptococci: Streptococcus pyogenes or Group A Beta-Hemolytic Streptococci
Bacterial structure
Fimbrae: attachment and adherence
M protein: major virulence factor
Hyaluronic acid capsule: prevents phagocytosis

20. Streptococcus pyogenes or Group A Streptococci: Additional Virulence Factors
Hemolysins
Streptolysin O
Streptolysin S
Erythrogenic toxin
Enzymes
Streptokinase
DNases
Hyaluronidase

21. Streptococcus pyogenes (Group A) Streptococcal Infections
Acute bacterial pharyngitis
Sore throat
Malaise
Fever/headache
Scarlet fever
Pyodermal infections
Impetigo
Erysipelas
Erysipelas due to Streptococcus pyogenes

22. Post–Group-A Streptococcal Infections
Rheumatic fever from pharyngeal infections only
Fever
Inflammation of the heart, joints, blood vessels, and subcutaneous tissues
Chronic, progressive damage to the heart valves

23. Post–Group-A Streptococcal Infections
Acute glomerulonephritis from either cutaneous or pharyngeal infections
More common in children than adults
Antigen-antibody complexes deposit in the glomerulus
Inflammatory response causes damage to the glomerulus and impairs the kidneys

24. Invasive Group A Streptococcal Infections
Streptococcal toxic shock syndrome
Multi-organ system failure similar to staphylococcal toxic shock
Initial infection may have been pharyngitis, cellulitis, peritonitis, or other wound infections

25. Invasive Group A Streptococcal Infections: “Flesh-Eating Bacteria”
Cellulitis
Severe form of infection that is life-threatening
Bacteremia and sepsis may occur
In patients necrotizing fasciitis, edema, erythema, and pain in the affected area may develop
Streptococcal myositis resembles clostridial gangrene

26. Laboratory Diagnosis: Group A Streptococcus
Grams stained wound smear showing gram-positive cocci in chains with numerous “polys”

27. Laboratory Diagnosis: Group A Streptococcus
Colony morphology
Transparent, smooth, and well-defined zone of complete or b- hemolysis

28. Laboratory Diagnosis: Group A Streptococcus
Identification
Catalase-negative
Bacitracin-susceptible
PYR-positive
Bile-esculin–negative
6.5% NaCl-negative
Group A streptococci is susceptible to Bacitracin disk (left); The right shows resistance

29. Group B b-Hemolytic Streptococcus (Staphylococcus agalactiae)
Has been known to cause mastitis in cattle
Colonize the urogenital tract of pregnant women
Cause invasive diseases in newborns
Early-onset infection
Late-onset disease

30. Staphylococcus agalactiae: Invasive Infections
Early-onset infection
Occurs in neonates who are less than 7 days old neonates
Vertical transmission of the organism from the mother
Manifests in the form of pneumonia or meningitis with bacteremia
Associated with a high mortality rate

31. Staphylococcus agalactiae: Invasive Infections
Late-onset infection
Occurs between 1 week and 3 months after birth
Usually occurs in the meningitis form
Mortality rate is not as high as early-onset
In adults
Occurs in immunosuppressed patients or those with underlying diseases
Often found in a previously healthy adult who just experienced childbirth

32. Laboratory Diagnosis: Group B b-Hemolytic Streptococcus
Colony morphology
Grayish-white, mucoid, creamy, narrow zone of b-hemolysis
Presumptive Identification tests
Catalase-negative
Bacitracin-resistant

33. Laboratory Diagnosis: Group B b-Hemolytic Streptococcus
Presumptive identification tests
Bile-esculin-hydrolysis–negative
Does not grow in 6.5% NaCl
CAMP-test–positive
S. agalactiae shows the arrow-shaped hemolysis near the staphylococcus streak, showing a positive test for CAMP factor

34. Identification Schema
Schema to differentiate Group A and B from other b-hemolytic streptococci

35. Streptococcus Group D and Enterococcus Species
Members of the gut flora
Associated infections
Bacteremia
Urinary tract infections
Wound infections
Endocarditis

36. Laboratory Diagnosis: Streptococcus Group D and Enterococcus Species
Microscopic morphology
Cells tend to elongate
Colony morphology
Most are non-hemolytic, although some may show a- or, rarely, b-hemolysis
Possess Group D antigen

37. Laboratory Diagnosis: Streptococcus Group D and Enterococcus Species
Identification tests
Catalase: may produce a weak catalase reaction
Hydrolyze bile esculin
Differentiate Group D from Enterococcus sp. with 6.5% NaCl or PYR test

38. Identification Schema
Schema to differentiate Enterococcus and Group D streptococci from other nonhemolytic streptococci

39. Other Streptococcal Species
Viridans group
Members of the normal oral and nasopharyngeal flora
Includes those that lack the Lancefield group antigen
Most are  hemolytic but also includes nonhemolytic species
The most common cause of subacute bacterial endocarditis (SBE)

40. Streptococcus pneumoniae
General characteristics
Inhabits the nasopharyngeal areas of healthy individuals
Typical opportunist
Possess C substance
Virulence factors
Polysaccharide capsule
Clinical infections
pneumonia
meningitis
bacteremia
sinusitis/otitis media

41. Laboratory Diagnosis: Streptococcus pneumoniae
Microscopic morphology
Gram-positive cocci in pairs; lancet-shaped

42. Laboratory Diagnosis: Streptococcus pneumoniae
Colony morphology
Smooth, glistening, wet-looking, mucoid
a-Hemolytic
CO2enhances growth

43. Laboratory Diagnosis: Streptococcus pneumoniae
Identification
Catalase negative
Optochin-susceptibility-test–susceptible
Bile-solubility-test–positive

44. Identification Schema
Schema to differentiate S. pneumoniae from other a-hemolytic streptococci

45. Streptococcus-Like Organisms
Aerococcus
Gram-positive cocci that tend to form tetrads
a-hemolytic; and may resemble viridans group
May be confused with Enterococcus biochemically

46. Streptococcus-Like Organisms
Leuconostoc
Resemble streptococci microscopically; colonies resemble viridans group or Enterococcus
Found in plants, vegetables, and dairy products
Pediococcus
Found in nature; used in bioprocessing and biopreservation of foods such as cheese, meats, and vegetables
Rarely seen in human infections; has been associated with septicemia

47. Points to Remember General characteristics and hemolytic patterns of
streptococcal and enterococcal species
Infections produced by pathogenic species
Microscopic and colony morphology
Tests used to identify these species
Emergence of resistant strains