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Questions and Answers
What term is used to describe the group that includes peptostreptococci?
What term is used to describe the group that includes peptostreptococci?
On what basis are aerobic and facultative anaerobic streptococci classified?
On what basis are aerobic and facultative anaerobic streptococci classified?
Which of the following statements is true regarding peptostreptococci?
Which of the following statements is true regarding peptostreptococci?
What type of bacteria includes streptococci that can survive in both aerobic and anaerobic environments?
What type of bacteria includes streptococci that can survive in both aerobic and anaerobic environments?
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Which of the following is NOT a way to classify streptococci?
Which of the following is NOT a way to classify streptococci?
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What characteristic do some strains exhibit during the logarithmic phase of growth?
What characteristic do some strains exhibit during the logarithmic phase of growth?
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What type of colonies do strains that produce a hyaluronic acid capsule develop on blood agar?
What type of colonies do strains that produce a hyaluronic acid capsule develop on blood agar?
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Which of the following is true about the catalase activity of the strains mentioned?
Which of the following is true about the catalase activity of the strains mentioned?
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During what phase of growth do strains produce a hyaluronic acid capsule?
During what phase of growth do strains produce a hyaluronic acid capsule?
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What impact does the presence of a hyaluronic acid capsule have on colony morphology?
What impact does the presence of a hyaluronic acid capsule have on colony morphology?
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What is the primary function of M protein in Streptococcus pyogenes?
What is the primary function of M protein in Streptococcus pyogenes?
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Which characteristic describes M protein?
Which characteristic describes M protein?
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Which classes of M protein are recognized in Streptococcus pyogenes?
Which classes of M protein are recognized in Streptococcus pyogenes?
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What role does M protein play in the virulence of Streptococcus pyogenes?
What role does M protein play in the virulence of Streptococcus pyogenes?
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What structural form does M protein take on the cell wall of S. pyogenes?
What structural form does M protein take on the cell wall of S. pyogenes?
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Which type of DNAase is considered the most common?
Which type of DNAase is considered the most common?
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In most patients who have had a recent infection with S. pyogenes, which DNAase is primarily associated with antibody development?
In most patients who have had a recent infection with S. pyogenes, which DNAase is primarily associated with antibody development?
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How many immunologically distinct types of DNAases are recognized?
How many immunologically distinct types of DNAases are recognized?
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Which type of DNAase is least commonly associated with antibody presence after infection with S. pyogenes?
Which type of DNAase is least commonly associated with antibody presence after infection with S. pyogenes?
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Which of the following statements is true regarding DNAases?
Which of the following statements is true regarding DNAases?
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What is a notable symptom of scarlet fever?
What is a notable symptom of scarlet fever?
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Which condition is associated with systemic symptoms and lymph node enlargement?
Which condition is associated with systemic symptoms and lymph node enlargement?
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Which of the following statements about impetigo is correct?
Which of the following statements about impetigo is correct?
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What is a common feature of pharyngitis caused by Streptococcus pyogenes?
What is a common feature of pharyngitis caused by Streptococcus pyogenes?
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Which of the following is a potential complication of streptococcal pharyngitis?
Which of the following is a potential complication of streptococcal pharyngitis?
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What shape is the S. pneumoniae when observed under the microscope?
What shape is the S. pneumoniae when observed under the microscope?
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What type of colonies does S. pneumoniae form on blood agar?
What type of colonies does S. pneumoniae form on blood agar?
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Which test can determine the sensitivity of pneumococci to optochin disc?
Which test can determine the sensitivity of pneumococci to optochin disc?
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What does the presence of mucus and amorphous debris in sputum indicate?
What does the presence of mucus and amorphous debris in sputum indicate?
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Which of the following is NOT used for the determination of pneumococci in fresh sputum?
Which of the following is NOT used for the determination of pneumococci in fresh sputum?
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Study Notes
Gram-positive Cocci Bacteria (Streptococci) - Overview
- Gram-positive cocci are spherical bacteria arranged in chains or pairs
- Streptococci are a diverse group of bacteria, often classified by carbohydrate antigens on their cell walls, using the Lancefield system (e.g., group A, B, C). Another classification system is based on hemolysis reactions
- Medically important streptococci include S. pyogenes (Group A), S. agalactiae (Group B), S. pneumoniae, viridans streptococci, and Enterococcus faecalis
- These bacteria have various characteristics, which include being non-spore-forming, non-motile, and facultative anaerobes
Streptococci: General Characteristics
- Typically gram-positive, spherical, and arranged in chains or pairs; often small, non-pigmented colonies, sensitive to drying, heat, disinfectants.
- Can form capsules and slime layers
- Do not produce catalase, but possess a peroxidase system.
- Most parasitic forms require enriched media for growth due to their fastidious nature.
Classification of Streptococci
- Lancefield classification is based on the type of carbohydrate antigens present on the cell wall.
- Another system is based on hemolysis, distinguishing between alpha-hemolytic (e.g., S. pneumoniae) and beta-hemolytic (e.g., S. pyogenes).
Streptococcus pyogenes (Group A)
- Most serious and common streptococcal pathogen; strict parasite of the throat and nasopharynx, occasionally skin.
- Laboratory characteristics: Culture on blood agar shows small, typically matt or dry colonies surrounded by beta-hemolysis. Some strains produce a hyaluronic acid capsule, evident in mucoid colonies on blood agar. Also catalase negative and bacitracin-sensitive.
Virulence Factors of S. pyogenes
- Surface antigens, such as C-carbohydrates and lipoteichoic acid (protect against lysozyme, aid in adherence), M proteins (antiphagocytic, major virulence factor), and hyaluronic acid capsules (protect against phagocytosis)
- Extracellular enzymes: streptokinase (lyses fibrin), hyaluronidase (breaks down hyaluronic acid), DNAases (deoxyribonucleases), NADase (kills leukocytes)
- Extracellular toxins: streptolysins O and S (hemolysins), pyrogenic toxin (erythrogenic) (causes scarlet fever), and superantigens (stimulate immune response)
Pathogenesis and Infections (S. pyogenes)
- Can cause suppurative infections (e.g., impetigo, pharyngitis, erysipelas, cellulitis; necrosing fasciitis, and streptococcal toxic shock syndrome)
- Can lead to nonsuppurative sequelae, like rheumatic fever and acute glomerulonephritis (immune response to bacterial antigens)
Epidemiology (S. pyogenes)
- Primarily occurs in childhood.
- Infections are spread by asymptomatic carriers.
- Rheumatic fever and acute glomerulonephritis were historically associated with poverty, implying a genetic predisposition to susceptibility.
- Entry portals are generally the skin or pharynx.
Host Defenses (S. pyogenes)
- Antibodies to M protein provide type-specific immunity.
- Antibodies to erythrogenic toxin prevent scarlet fever rash.
- Immune mechanisms are critical to acute rheumatic fever and glomerulonephritis development.
Laboratory Identification (S. pyogenes)
- Grown on blood agar with pronounced hemolytic activity, enhanced anaerobically. Catalase-negative.
- Bacitracin sensitivity, testing for group (A)-specific carbohydrates, identification of L-pyrrolidonyl arylamidase enzyme (PYR).
- Anti-streptolysin O (ASO) test to confirm rheumatic fever or glomerulonephritis.
- Anti-DNAse B test used for glomerulonephritis.
S. pneumoniae
- Causes 60-70% of bacterial pneumonias. Gram-positive diplococci, with short chains and lancet shapes
- Culture requires blood or chocolate agar; improved growth with 5-10% CO2.
- All pathogenic strains form large capsules (a major virulence factor).
- Causes lobar pneumonia, acute exacerbation of chronic bronchitis often with Haemophilus influenzae, meningitis, otitis media, sinusitis, and conjunctivitis (especially in splenectomized patients).
S. pneumoniae: Epidemiology
- 5-50% of people carry as normal flora in the nasopharynx.
- Infections are typically endogenous in origin. Pneumonia occurs when cells are aspirated into lungs.
- Susceptibility is influenced by factors such as young age, immune compromise, viral infections, and living conditions.
S. pneumoniae: Laboratory Diagnosis
- Gram stain of specimen; a hemolytic, optochin-sensitive bacteria; Quellung test (capsular swelling reaction)
- Culture on blood agar, showing alpha hemolysis, sensitive to optochin disk.
- Definitive diagnosis with culture and microscopic confirmation of characteristic diplococcal morphology.
S. pneumoniae: Treatment and Prevention
- Traditionally treated with penicillin G or V; increased drug resistance, making alternative antibiotics necessary.
- Two vaccines available: one targeting older adults (PPSV23) and another for children (PPV13), to decrease mortality risk.
Alpha-hemolytic Streptococci (Viridans Group)
- Alpha-hemolytic (viridans = green).
- Lack Lancefield group-specific carbohydrates.
- Normal microbiota of the mouth, pharynx, stomach, and urinary tract.
- Opportunistic pathogens causing dental caries, and dental plaques; capable of causing meningitis and endocarditis
Group D Enterococci and Groups C and G Streptococci
- Enterococcus faecalis, E. faecium, E. durans are normal intestinal flora
- Cause opportunistic urinary, wound and skin infections, particularly in debilitated patients.
- Group C and group G are frequently found in upper respiratory tract infections, pharyngitis, glomerulonephritis and bacteremia.
- Some group D non-enterococci (e.g., S. bovis) have been reclassified and are taxonomically significant, distinguished by being PYR negative and bile esculin positive.
Streptococci: Treatment and Prevention
- Streptococcal infections are traditionally treated with penicillin, but resistance to penicillin has become a concern. Erythromycin is used if penicillin is contraindicated.
- Resistance to erythromycin can also occur but is less prevalent.
- Vaccines are available to prevent Streptococcus pneumonia and some forms of Group A Streptococcus infections.
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Test your knowledge on streptococci classification and characteristics with this quiz. Explore topics such as peptostreptococci, anaerobic survival, and the significance of M protein in Streptococcus pyogenes. Perfect for microbiology students and enthusiasts!
