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WVSOM - Strep
Streptococci
Question | Answer |
---|---|
General properties of Streptococci | Gram + cocci in chains; catalase -; ferments sugars -> lactic acid -> low pH; require enrichment with blood to support growth |
How are Streptococci classified? | Based on c-carbohydrate (Lancefield groups A-U); preliminary grouping based on hemolysis of 5% sheep blood (beta-hemolysis, alpha-hemolysis, gamma-hemolysis) |
Classification of S. pyogenes | Beta-hemolysis, Lancefield group A, bacitracin S lab test |
Classification of S. agalactiae | Beta-hemolysis, Lancefield group B, hippurate hydroylsis + lab test |
Classification of S. faecalis | Gamma (alpha)-hemolysis, Lancefield group D, bile esculin + lab test |
Classification of S. pneumoniae | Alpha-hemolysis; optochin S, bile solubility +, quelling test + lab tests |
Name 4 clinically important Streptococci | S. pyogenes, S. agalactiae, S. faecalis, S. pneumoniae |
Describe the structural virulence factors of S. pyogenes | Capsule - hyaluronic acid, fibrils - consist of m-protein and lipoteichoic acid, peptidoglycan layer, T and R proteins |
List some soluble virulence factors of S. pyogenes | Streptokinase, streptodornase, hyaluronidase, erythrogenic toxin, nicotinamide adenine dinucleotidase (NADase), streptolysins (hemolysins) |
List 2 types of S. pyogenes streptolysins | Streptolysin O - oxygen labile, antigenic; streptolysin S - oxygen stabile, non-antigenic |
How do you encounter S. pyogenes? | Acquired through another infected individual or carrier |
How does S. pyogenes spread? | Group A highly adapated to resist phagocytosis and spread through tissues |
What damage does S. pyogenes cause? | Elicits a strong immune response: causes release of chemotaxins for WBCs, activates complement by alternate pathway, resists phagocytosis and kills many of invading cells |
What results from the lysis of WBCs in an S. pyogenes infection? | WBCs release lysosomal enzymes, which damages surrounding tissue |
What are some localized infections caused by S. pyogenes? | Pharnyngitis (sore throat), scarlet fever, impetigo |
What are some invasive infections caused by S. pyogenes? | Wounds, ersipelas, cellulitis, puerperal fever, endocarditis |
What are some post-infection diseases caused by S. pyogenes? | Rheumatic fever, glumerulonephritis |
How is pharyngitis diagnosed? | Throat cultures, direct antigen test |
How are invasive infections diagnosed? | Gram stain and culture, blood culture if bacteremia is suspected |
What 2 tests are available to detect the presence of antibodies to S. pyogenes? | Streptozyme test (screens for ASO, anti-DNAase B, AHase, & anti-NAD); antistreptolysin O (ASO) titer (quantitate Ab to streptolysin O) |
What is the underlying reason for the rash produced in scarlet fever? | Erythrogenic toxin produced by lysogenic group A streptococcus causes rash |
How many times can you get scarlet fever? | Typically, only once |
What is used to treat S. pyogenes? | Penicillin, prevention against rheumatic fever (long acting penicillin G, oral penicillin for 10 days) |
What diseases are caused by S. agalactiae? | Septicemia, meningitis, pneumonia |
Who does S. agalactiae typically infect? | Neonates |
S. agalactiae belongs to which group? | Group B strep |
Diseases caused by S. faecalis | UTIs, wounds, sepsis |
S. faecalis belongs to which group? | Group D strep |
S. faecalis is also known as | Enterococcus faecalis |
Viridans strep / alpha strep causes ... | Subacute endocarditis, dental caries (S. mutans) |
S. pneumonia causes ... | Pneumonia, otitis media, sinusitis |
Example of gram - nonfermenter | Pseudomonas aeruginosa |
What are gram - nonfermenters? | Opportunistic pathogens that do not ferment glucose |
Charactersitics of P. aeruginosa | Motile w/ polar flagella, oxidase +, obligate aerobes, grow at 42C, colonies produce fruity odor |
What are some virulence factors that contribute to P. aeruginosa? | Pili, polysaccharide capsule (slime layer) - resists killing by antibiotics, endotoxin (LPS), many extracellulr enzymes, exotoxin A - causes ADP-ribosylation of elongation factor 2 -> inhibits protein synthesis |
What are some diseases caused by P. aeruginosa? | Skin infections following burns; super infections following use of broad-spectrum antibiotics; wounds; colonize respirators pneumonia; colonize respiratory tract in patients w/ cystic fibrosis pneumonia; conjuctivitis; otitis externa; folliculitis |
How can folliculitis be acquired? | Hot tubs or swimming pools |
Prevention and treatment of P. aeruginosa? | Clean rooms & sterilize hospital equipment; replace plastic tubing; minimize unnecessary broad-spectrum antibiotics & prophylaxis; aminoglycoside + piperacillin / ticarcillin by IV |
General features of Acinetobacter | Oxidase -, aerobic, nonfermentative, nonmotile, pleomorphic, short gram - rods |
Name 2 types of Acinetobacter | A. anitratus, A. baumanii |
Characterize A. anitratus | Cause variety of nosocomial infections similar to Pseudomonas, naturally resistant |
Characterize A. baumanii | Opportunistic infections, American soldiers wounded in Iraq, multiple drug resistant (MDRAB) |
Which 2 acinetobacter are responsible for > 90% of reported cases? | A. baumanii, A. calcoaceticus |
A. baumanii, A. calcoaceticus | Prevalent in American soldiers wounded in Iraq, multiple drug resistant (MDRAB), cause variety of opportunistic & nosocomial infections (similar to Pseudomonas in temperate climates) |