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Micro lecture 15.2
Micro lecture 15.2 Streptococcus
| Question | Answer |
|---|---|
| What does streptococcus look like? | Gram-positive cocci arranged in pairs or chains. Facultative anaerobes, catalase negative. |
| What are the 3 classification schemes of streptococci? | Hemolysis on BAP, Serologic properties, and biochemical properties. |
| What is Lancefield serological grouping? | β-hemolytic streptococci are found on humans. They have specific carb. antigens (streptococcal grouping antigens). The antigens can be extracted and then identified by treating with antisera into three groups: A, B, and C. |
| Group A streptococcus (GAS) | S. pyogenes affects humans, rodents, and dairy cattle. |
| Is GAS β-hemolytic? | yes |
| Name the pus-forming diseases GAS causes. | Pharyingitis, scarlet fever, pyoderma (impetigo), erysipelas, cellulitis, necrotizing fasciitis, streptococcal TSS |
| Name the non-suppurative diseases GAS causes. | Rheumatic fever, acute glomerulonephritis |
| Name some virulence factors of S. pyogenes. | Capsule, Lipoteichoic acids, M protein, F protein, Pyrogenic exotoxins, SLS, SLO, Streptokinase, DNase, C5a peptidase, hyaluronidase |
| Capsule of hyaluronic acid | antiphagocytic and aids tissue invasion |
| Lipoteichoic acids | binds to oral epithelial cells |
| M protein | adhesin that mediates internalization by host cells. |
| F protein | binds fibronectin |
| Pyrogenic exotoxins | mediate systemic toxicity; cause fever, rash, scarlet fever; most are superantigens, |
| Streptolysin S (SLS) | O2 stable, lyses WBC and RBC, nonimmunogenic |
| Streptolysin O (SLO) | O2-labile, lyses WBC and RBC and other cells, pores formed provide entry into cells by toxins |
| Streptokinase | lyses blood clots |
| DNase | degrades DNA released from lysed WBCs in pus |
| C5a peptidase | suppresses inflammatory response and WBC recruitment |
| hyaluronidase | degrades hyaluronic acid of connective tissue ground substance |
| What's the best way the host kills GAS? | phagocytosis and intracellular killing within PMNs |
| Why is M protein important? | GAS is not infectious without it. They are antiphagocytic and interfere with opsonization by complement. |
| Scarlet fever occurs when... | the infecting GAS bacterium is lysogenized by a temperate phage that produces streptococcal pyrogenic toxins A or C. |
| Impetigo is caused by... | both S. aureus and GAS, usually. |
| What does cellulitis look like? | Skin that's blotched pink and warm, with indistinct margins. |
| What does erysipelas look like? | Severe cellulitis, deep-red inflammation with well-defined margins. |
| Necrotizing Fasciitis | is nasty to look at, necrosis around a cut, often accompanied by TSS, needs aggressive surgical care. |
| Streptococcal TSS | intense cytokine release due to superantigens. |
| What is the example of GBS? What does it cause? | S. agalactiae; causes mastitis in dairy cattle and neonatal diseases in humans. |
| What does early onset neonatal disease do? | Within 7 days of birth develop pneumonia, meningitis, and sepsis |
| What does late onset neonatal disease do? | over 1 week after birth, bacteremia with meningitis |
| What does GBS look like in pregnant women | Present as a UTI; may involve bacteremia |
| What does GBS look like on a BAP? | Large colonies, with small area of β-hemolysis around the colony. |
| What is the CAMP test for GBS? | CAMP factor is a diffusible, heat stable protein that GBS form that enhances β-hemolysis of S. aureus. A positive test looks like an arrowhead on an S. aureus streak. |
| What is a nongroupable example? | S. pneumoniae; it lacks the carbohydrate on which Lancefield groupings are based. |
| What does S. pneomoniae look like? | A-hemolytic, lancet shaped diplococci. When Gram-stained, capsule does not color. |
| What are some virulence factors of S. pneumoniae? | Capsule, IgA protease, pneumolysin, adhesins, DNase |
| What diseases does S. pneumoniae cause? | Pneumonia, Meningitis, Bacteremia, Sinusitis and Otitis media (middle ear infection) |
| What does A-hemolysis look like on a BAP? | Greening of the agar |
| What are some examples of Viridans Streptococci? | S. mutans and S. mitis |
| What type of hemolysis do they do? | Alpha or Gamma. |
| What are 2 types of Streptococci important to vets? | S. equi and S. canis |
| What are the 2 most common Enterococci that produce disease in humans? | E. faecalis and E. faecium |
| What did Enterococcus used to be? | GDS |
| What does Enterococcus look like? | pairs and short chains of lancet-shaped cells |
| What are the characteristics of Enterococcus? | grow in 6.5% NaCl or 40% bile salts; hydrolyze esculin in presence of bile salts; PYR positive; react with group D antiserum |
| What diseases does Enterococcus cause? | UTIs, peritonitis, endocarditis |
| Enterococci are ___________ resistant to many antibiotics. | Inherently |
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