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Gram Positive 1
Duke PA micro
Question | Answer |
---|---|
Streptococci | diverse group of gram positive cocci |
How are streptococci arranged? | pairs or chains |
What are the oxygen requirements for streptococci? | facultative anaerobes with complex nutritional requirements |
What are the classifications of streptococci? | serology (Lancefield groups), hemolytic patterns, biochemical (species name), clinical presentation |
Lancefield groups | refers to group-specific cell wall antigens (usually carbohydrates) |
What is the current use of the Lancefield groups? | groups A, B, C, F and G |
Hemolysis | bacterial growth on blood agar surface disrupts erythrocytes |
classification of Streptococcus by hemolysis | A-hemolytic, B-hemolytic or non-hemolytic |
A-hemolysis on blood agar | zone of hemolysis on blood agar appears green |
B-hemolysis on blood agar | zone of hemolysis is clear |
non-hemolytic example | Streptococcus pneumoniae |
viridans streptococci | normal flora of human upper respiratory and GI tract, can cause |
important viridans streptococci | |
viridans streptococci normal flora - where? | human upper respiratory and GI tract |
What age is strep most common? | 5-15 year olds |
What are viridans streptcocci normal flora involved in? | |
B-hemolytic streptococci - Group A | colonize upper respiratory tract of children, and, to a lesser extent, adults |
B-hemolytic streptococci - Group B | normal flora of perineum in 1/3 of adults |
Most of the B-hemolytic streptococci also carry what other designations? | Lancefield - Groups A, B, C and G |
What needs to always be on the differential for neonates? | Group B strep |
Who is at risk for B-hemolytic Group B strep? | pregnant women - transmitted strep to neonate could be very harmful |
B-hemolytic streptococci - Group C | similar spectrum to Group A |
B-hemolytic streptococci - Group G | infections of skin |
What should always follow a rapid test, negative or positive? | culture |
What type of strep do most labs check for? | B-hemolytic Group A strep |
What could you miss with just a reguluar strep culture? | B-hemolytic Group B strep - similar to Group A |
Group A Strep aka | S. pyogenes |
What is Group A Streptococci often designated as? | GAS |
What is the most common clinical picture of GAS? | exudative pharyngitis |
What else can GAS cause? | various other clinical syndromes |
Why do we treat streptococcal pharyngitis? | to prevent rheumatic fever |
What are the virulence factors of GAS? | M-proteins, adhesins, capsule, exotoxins |
M-proteins | surface cell wall proteins that facilitate spread through host tissue; strain specific |
Adhesins | numerous; facilitate adherence to host cells |
What are examples of adhesins? | lipotechoic acid, F-protein |
Capsule | resists phagocytosis |
What are the exotoxins in GAS? | streptolysins, streptokinase, pyrogenic exotoxins |
What do streptolysis do? | lyse RBCs, WBCs & plts |
What do streptokinases do? | lyse blood clots |
What do pyrogenic exotoxins do? | facilitate release of cytokines |
Exotoxins | species-specific proteins secreted (extracellularly) by bacteria |
What are some of the most powerful human poisons? | exotoxins |
Where are exotoxins secreted from? | both Gram + and Gram - bacteria |
What are endotoxins associated with? | Gram - bacteria |
What are some features of exotoxins? | virulence, antigenic, some are superantigens, unstable; heat labile |
Do exotoxins have broad or narrow cell type specificity? | either |
Group B streptococci aka | S. agalactiae |
Group B strep normal flora | of perineum in 1/3 of population |
Who are at increased risk of perinatel infections from Group B strep? | neonates |
Does Group B strep cause GU infections? | infrequent |