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WVSOM - Strep

Streptococci

QuestionAnswer
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)
Created by: JaneO