Staphylococci

1. Nomenclaturea. coagulase positive: primarily Staphylococcus aureus

• Coagulase test

b. coagulase negative: many species of Staphylococcusc. microdase positive: Micrococcus species

• modified oxidase test

2. Epidemiologya. Normal flora of skin and mucosab. Carrier state high in normal population

• easily transmitted

3. Pathogenesisa. localized skin infections

• follicles, boils, furuncles, carbuncles

http://dermatology.about.com/od/infectionbacteria/tp/bacterial_infections.htm

Furuncle Carbuncle

3. Pathogenesisb. toxin mediated diseases

• Enterotoxin: food poisoning• Exfoliatin: scalded skin syndrome• TSST-1: toxic shock syndrome• Pantone-Valentine Leukocidin?

3. Pathogenesisc. systemic infections

• all species: bacteremia• S. saprophyticus: UTI• Central Nervous System (CNS): indwelling devices (catheters,

valves, hardware, shunts)

d. antimicrobial resistance• Methicillin Resistant Staphylococcus aureus (MRSA)

– nosocomial v. community (PVL as marker?)– screening programs to detect colonization in hospitalized patients

• Vancomycin Intermediate Staphylococcus aureus (VISA)– thicker cell wall, grow poorly, vanco less active

• VRSA – vancomycin resistant– MRSA acquire plasmids containing van genes from Vanco resistant

enterococci (VRE)

Streptococci

1. Nomenclaturea. Hemolytic criteria: alpha, beta, gammab. Lancefield group carbohydrates for beta-hemolytic streptococci: A, B, C, F, Gc. some beta-hemolytic streptococci produce identical carbohydrate antigens in unrelated species, and some genetically related species have heterogeneous carbohydrate antigens

2. Epidemiologya. normal flora of skin, mucosa (upper

respiratory tract, GU tract, GI tract)

b. disease can be due to person-person transmission or from endogenous strains

3. Pathogenesis

a. S. pyogenesi. Group A, beta-hemolytic

ii. acute pharyngitis, skin infections, bacteremia with potential for severe systemic effects

– toxic shock syndrome, necrotizing faciitis (“flesh-eating” disease)

iii. many toxins, enzymes, M protein which are all virulence factors

iv. post infection sequelae: Rheumatic fever, acute glomerulonephritis (AGN)

• reason for treating strep throat is to prevent these

b. S. agalactiaei. Group B, beta-hemolyticii. neonatal infections following PROM

early onset (day 0 – 5) late onset (day 7 – 90)

iii. screening of pregnant women at week 35- 37

c. S. pneumoniaei. alpha hemolyticii. pneumonia, meningitis, and otitis mediaiii. capsule has antiphagocytic activity

23 valent polysaccharide vaccine for adults 7 valent conjugated vaccine for kids

c. Enterococcusi. alpha, beta, or gamma hemolyticii. most infections are nosocomial: UTI, bacteremia,

endocarditisiii. multi-drug resistance contributes to pathogenesis;

penicillins, aminoglycosides, glycopeptides E. faecalis, vanA, vanB (plasmid, inducible) E. faecium, vanA, vanB (plasmid) E. gallinarum, vanC (chromosome) E. casseliflavus, vanC (chromosome)

d. Viridans streptococci and Abiotrophia sp.i. normal skin flora; non-pathogensii. endocarditis in compromised hosts iii. alpha hemolyticiv. Abiotrophia show satelliting

C. Identification algorithms

1. Gram stain: pairs, chains, clusters

2. Direct antigen detection

a. GAS from throat

b. Pneumococcus from CSF or blood cultures

3. Selective media

a. SSA for GAS from throat

b. GBS broth + Grenada agar

4. catalasea. positive: coagulase

i. positive: CPS (S. aureus)ii. negative: CNS

Yellow pigment: Micrococcus high numbers in urine, screen for Staphylococcus saprophyticus using

novobiocin (R = S. saprophyticus)

b. negative: hemolysisi. beta: typing: A, B, C, D, F

streptolysin O, S CAMP test for GBS

ii. alpha: optochin sensitive: S. pneumoniae resistant: Alpha-hemolytic streptococci

iii. gamma: PYR positive: Enterococcus

motile: E. casseliflavus or E. gallinarumnon-motile: biochems for E. faecalis or E. faecium

negative: Gamma-hemolytic streptococci

http://www.bact.wisc.edu/Microtextbook/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=35&page=1

Staphylococcus sp. on Gram stain

S. aureus, beta-hemolytic

S. aureus, gold colonies

Coagulase-negative Staphylococci

Micrococcus sp., yellow colonies

MRSA chromogenic agar

http://www.life.umd.edu/classroom/bsci424/PathogenDescriptions/StreptococcusImages.htm

Streptococcus sp. on Gram stain

GBS GAS

Alpha-hemolytic S. pneumoniae Optichin-sensitive S. pneumoniae

Satelliting of AbiotrophiaCAMP positive GBS

S. agalactiae (GBS) on Grenada agar

D. Susceptibility testing1. Staphylococcus sp.

a. resistance in multiple classes

b. usually test all S. aureus; test Coag Neg Staph if appropriate

c. VITEK, disk diffusion or broth dilution

d. inducible clinda resistance

2. GAS, GBSa. not resistant to pen, ceph, vanco

b. resistance to macrolides, so test if considering use

c. disk diffusion or broth dilution

d. inducible clinda resistance in GBS

D. Susceptibility testing3. S. pneumoniae

a. resistance to pen, ceph, macrolides

b. VITEK, disk diffusion or broth dilution

c. different interpretive criteria for CNS v. non-CNS infections

4. Enterococcusa. usually use cell wall active agent plus aminoglycoside to achieve sufficient bactericidal activity

b. resistance to all clinically useful agents has been documented

c. test using broth dilution, including high level resistance to aminoglycosides (VITEK)

5. other strep (not routine)