Questions and Answers
What type of organism is Streptococcus?
What is the classification basis of the genus Streptococcus?
Hemolytic properties on blood agar and serologic group.
Name one condition that can result from streptococci infection?
Septicemia.
What is hemolysis?
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Alpha hemolysis appears as a clear, red blood cell-free zone surrounding the colony.
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Match the following types of hemolysis with their descriptions:
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What does the Lancefield system classify?
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What is a key virulence factor of Streptococcus pneumoniae?
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Group A beta streptococci show sensitivity to bacitracin.
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What is Enterococcus faecalis associated with?
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Which of the following is a characteristic of the genus Enterococcus?
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What is the role of bile esculin agar in the identification of enterococci?
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What causes rheumatic fever?
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Taxo A® disc is used to test sensitivity to optochin.
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Study Notes
Streptococci and Enterococci Overview
- Streptococci and Enterococci are gram-positive (G+) cocci that are catalase negative, meaning they do not produce bubbles when exposed to hydrogen peroxide.
- Streptococci are classified based on hemolytic properties observed on blood agar and through serologic grouping.
Classification of Streptococci
- Major types include beta streptococci, pneumococcus (Streptococcus pneumoniae), and viridans streptococci.
- Hemolysis types: alpha (partial), beta (complete), and gamma (no hemolysis).
Pathogenic Spread of Streptococci
- Originating from the pharynx, streptococci can cause various respiratory infections (laryngitis, bronchitis, pneumonia, otitis media).
- Can disseminate to cause severe conditions such as septicemia, osteomyelitis, endocarditis, septic arthritis, and meningitis.
- Can infect skin, leading to erysipelas, impetigo, and cellulitis.
Hemolysis Characteristics
- Hemolysis refers to the breakdown of red blood cells due to bacterial enzymes like hemolysins.
- Beta hemolysis results in a clear zone around colonies, indicating complete lysis of red blood cells. Alpha hemolysis shows a greenish discoloration, and gamma hemolysis shows no change.
Lancefield Classification System
- Streptococci are categorized into serologic groups (A, B, C, D, E, F) based on carbohydrate antigens in their cell walls.
- Group A beta streptococci (Streptococcus pyogenes) cause most acute human infections, like streptococcal sore throat.
Group A Beta Streptococcus - Streptococcus Pyogenes
- Appearance: Small, white opaque colonies with beta hemolysis.
- Spread primarily through respiratory droplets. Skin infections arise from direct contact.
- Causes autoimmune diseases such as rheumatic fever and acute glomerulonephritis due to hypersensitivity responses.
Identification Techniques for Streptococcus Pyogenes
- Cultured on stabbed blood agar with a Taxo A disc.
- Sensitivity to bacitracin (tested by the Taxo A disc) is a distinctive feature.
- Hemolysin Streptolysin O is inactivated by oxygen, facilitating deeper hemolysis where oxygen levels are low.
Identification of Pneumococcus - Streptococcus Pneumoniae
- Normal flora of the nasopharynx but a common cause of community-acquired pneumonia.
- Passport features: mucoid translucent colonies, alpha hemolysis, optochin sensitivity (via Taxo P disc), and bile solubility test.
- Gram-stained sputum reveals encapsulated, gram-positive, lance-shaped diplococci.
Enterococcus Genus
- Enterococci are G+ streptococci found in the intestinal tract, notable for causing opportunistic infections.
- Highly antibiotic-resistant; responsible for nosocomial urinary infections, wound infections, and bacteremia.
Key Species - Enterococcus Faecalis
- Most common enterococcus in humans.
- Isolated from infections in the peritoneal cavity, urinary tract, kidneys, and damaged skin.
Isolation Techniques for Enterococci
- SF broth: Contains sodium azide to inhibit most bacteria except enterococci. Color change indicates pH shift from acid production.
- Bile Esculin agar: Enterococci grow in bile salts and hydrolyze esculin, turning the agar black due to esculetin-iron salt reaction.
Group F and G Streptococci
- Group F (mainly S. anginosus): Associated with brain, mouth, and jaw abscesses and endocarditis.
- Group G: Show beta hemolysis; can cause pharyngitis and severe infections in compromised hosts, including endocarditis and bacteremia.
Group C Streptococci
- Primarily involve S. equi, S. equisimilis, and S. zooepidemicus.
- Beta hemolytic and common pathogens in animals, occasionally impacting humans.
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Test your knowledge of Streptococci and Enterococci with these flashcards. Learn about their classifications, properties, and definitions to enhance your understanding of microbiology. Perfect for lab preparation and review.
