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Streptococci and Other Streptococci-like Organisms

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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

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