Questions and Answers
Which group of Lancefield classification includes the species Streptococcus pyogenes?
What characteristic is NOT true for Streptococcus and Enterococcus species?
Enterococcus is classified under which Lancefield group?
What type of haemolysis can Streptococcus species exhibit?
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What is the incubation temperature range for Streptococcus and Enterococcus species?
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Which groups of β-haemolytic streptococci are commonly associated with human disease?
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Which of the following characteristics correctly describes β-haemolytic streptococci?
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What is the effect of vaccination in patients with asplenia?
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What is a common clinical characteristic of pneumonia caused by β-haemolytic streptococci in individuals over 50?
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Which species of β-haemolytic streptococci is associated with large colony size in Lancefield Group A?
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Study Notes
Streptococcus and Enterococcus Overview
- Greek origin of "Streptus" means “easily bent or twisted,” which reflects the chain-like formation of these bacteria.
- Streptococcus belongs to the family Streptococcaceae, while Enterococcus is classified under Enterococcaceae.
Classification
- Classification is based on:
- Serological (Lancefield) typing
- Hemolysis pattern on blood agar (BA)
- Biochemical tests
- Streptococcus has over 100 identified species; Enterococcus consists of more than 54 species.
Bacterial Characteristics
- Both are Gram-positive cocci, typically found in pairs or chains, measuring 0.5 - 2 µm.
- They are facultative anaerobes, with some being capnophilic (notably Streptococcus pneumoniae).
- Require enriched media for growth, except non-fastidious Enterococcus, and have an optimal incubation temperature of 35-37°C.
- May display hemolytic properties: α-, β-, or non-hemolytic (γ-hemolysis).
- They are catalase-negative, fermentative, non-spore-forming, and non-motile.
Common Infections
- Major causes of human infections are within three Lancefield groups:
- Group A (Streptococcus pyogenes)
- Group B (Streptococcus agalactiae)
- Group C (varied streptococcal species)
- Rare infections can arise from Groups E, F, G, and L, with Group D representing the Enterococcus genus which was previously categorized under Streptococcus.
β-Hemolytic Streptococci Characteristics
- Gram-positive cocci arranged in chains, measuring 1-2 µm.
- Form β-hemolytic colonies on blood agar, which are white, convex, and ≤ 1-2 mm in diameter.
- Notably susceptible to bacitracin and negative in the pyrrolidonyl arylamidase (PYR) test.
Notable Species in Human Disease
- Group C, G, and F are commonly associated with infections:
- Important species include Streptococcus dysgalactiae (Groups C and G) and Anginosus group (Groups A, C, F, G or non-group).
- Small colony size in Anginosus group indicates variations based on group affiliation.
Prevention and Vaccination
- Infants are recommended to receive the 13-valent conjugated pneumococcal vaccine at ages 2, 4, 6, and 12-15 months.
- Vaccine effectiveness depends on prevalent serotypes responsible for invasive disease and is notably poor in certain populations (asplenia, sickle cell disease, etc.).
Clinical Characteristics of Infections
- Early onset infections occur within the first week of life, often presenting with respiratory distress, fever, lethargy, and hypotension.
- Late onset infections manifest between 7 days to 3 months post-birth.
- Streptococcus pneumoniae is a significant cause of bacterial pneumonia in children (under 5 years), individuals over 50, and those with weakened immune defenses.
- Clinical symptoms of pneumonia include sudden onset chills, high fever, cough with rusty to pink sputum, and pleuritic chest pain.
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Description
Explore the classifications and characteristics of Streptococcus and Enterococcus in this Medical Microbiology quiz. Learn about serological typing, haemolysis, and biochemical tests in relation to these important bacterial genera.
