Terms in this set (38)
First gen cephalosporins can be adequately represented by:
-- cefotetan & cefotoxin (2nd gen)
-- ceftriaxone (3rd gen)
An antibiotic that inhibits cell wall synthesis is:
-- inhibits peptidoglycan (cell wall) synthesis
Which orgs doesn't require susceptibility testing when isolated from a clin-sig source?
S. aureus (clindamycin); Proteus mirabilis (gentamicin); Strep. pyogenes (penicillin); E. coli (levofloxacin)
Streptococcus pyogenes (penicillin)
-- penicillin resistance of S. pyo has not been documented
Which of the following antibiotics would routinely be tested and reported for isolates of Pseudomonas aeruginosa?
penicillin; erythromycin; clindamycin; gentamicin
-- others are not active against P. aeru
Which must be incubated in a microaerophilic environment for optimal recovery?
Campylobacter jejuni; E. coli; P. aeruginosa; Proteus mirabilis
-- most Campy grow best in 5% O₂, 10% CO₂, 85% N
Vibrio parahaemolyticus can be isolated best from feces on what type of agar?
thiosulfate citrate bile salts (TCBS) agar
-- highly selective and differential for Vibrio spp.
Which of the following media can be used to culture Campylobacter jejunum?
Skirrow medium; CIN agar; anaerobic CNA agar; bismuth sulfite
-- enriched selective blood agar for Campy isolation from specimens w/ mixed flora
-- CIN (Y. enterolitica); bismuth sulfite (Samonella); CNA(selective for g-pos)
Tests for beta-lactamase production in Haemophilus influenzae should be performed on:
all blood and CSF isolates
-- 20-40% of H. influenzae prod. beta-lactamases
Media used to support growth of Legionella pneumophila should contain what additives?
X & V factors; hemin & vit K; charcoal & yeast extract; dextrose & laked blood
charcoal and yeast extract
-- buffered charcoal yeast extract medium is specialized for isolation of Legionella
The best medium for culture of Bordetella pertussis is:
-- cephalexin inhibits nasopharyngeal flora
-- better isolation of B. pertussis than Bordet-Gengou
The best medium for culture of Francisella tularensis is:
cystine glucose blood agar
-- cystine is required by F. tularensis
[MLS] The most rapid method for detection of Francisella tularensis is:
When processing throat swabs for a group A Streptococcus culture, the medium of choice is:
sheep blood agar
-- because clear cut patterns of hemolysis are obtained
The ability to detect oxacillin-resistant S. aureus may be enhanced by:
using Mueller-Hinton broth w/ 2% NaCl
-- incubate plates at 35±2℃ for 24 hrs
The optimal wound specimen for culture of anaerobic organisms should be:
a syringe filled w/ pus, obtained before admin. of antibiotics
-- swabbing exposes orgs. to air
A 21 yo presents w/ pharyngitis. A throat swab is collected and submitted for anaerobic culture. The specimen should be:
rejected as unacceptable
-- anaerobes are commensal in oropharynx and do not cause pharyngitis
-- most common cause of it is Strep. pyo.
An antibiotic used to suppress or kill contaminating fungi in media:
-- common agent in Mycosel®
-- penicillin, streptomycin do not inhibit fungi
Production of beta-lactamase is inducible in:
H. influenzae; Staph. aureus; Corynebacterium diptheriae; Strep. pyogenes
-- only after exposure to inducing agent (penicillin)
-- H. influenzae (& Enterococcus spp., N. gonorrhoeae) continually prod. it
#65 Needs pic
request a new specimen
-- >10/lpf of squamous epithelial cells (SECs) is unacceptable
-- classic bacterial meningitis shows hi WBC (mostly neutrophils), low glucose, hi protein in CSF
-- well w/ lowest conc. of antibiotic showing no growth is the minimum inhibitory concentration (MIC)
When using a control strain of S. aureus, the tech notices the zone around oxacillin disk is too small. What is the most likely explanation?
expired oxacillin disks
[MLS] In disk diffusion method, the size of the inhibition zone used to indicate antibiotic susceptibility has been determined by:
correlating the zone size w/ minimum inhibitory concentrations (MIC)
What organism may be mistaken fo N. gonorrhoeae in Gram stained smears of uterine cervix exudates?
-- g-neg coccobacillus often plump and in pairs
-- occurs when vaginal secretions contaminate endocervical specimens
A 73 yo man Dx w/ pneumococcal meningitis is not responding to penicillin therapy. What test will best determine the orgs penicillin susceptibility?
beta-lactamase; oxacillin disk diff.; penicillin disk diffusion; Schlicter test
oxacillin disk diffusion
-- oxacillin is only disk diff. test recomm. for testing S. pneumoniae, which doesn't prod. beta-lactamase
-- Schlicter test does not detect antibiotic susceptibility
Which antimicrobial would be inappropriate to report on E. coli isolated from a wound culture?
gentamicin; ampicillin; cefazolin; nitrofurantoin
-- some antimicrobials, like this and norfloxacin, used only for UTIs and no where else
clindamycin result should be removed since it is inactive against Enterococcus
erythromycin: resistant; clindamycin: susceptible
-- this is the D test (negative) since no flattening of zone between E, CC disks
-- means clindamycin resistance is not inducible
Which of the following combos is useful for confirming the presence of extended spectrum beta-lactamases (ESBL) in E coli?
ampicillin+cefepime; cefotoxin+penicillin; ceftazidime+clavulanic acid; cefpodoxime+cefotaxime
-- ESBLs are inhibitied by clavulanic acid
What is the most important variable in the recovery of organisms in pt. with bacteremia?
vol. of blood cultured
-- many cases are lo magnitude, so there is a direct relationship btwn blood yield and culture positivity
-- g-neg diplococci w/in or closely assoc. w/ neutrophils in smears from urethral discharge
CHOC agar incubated in CO₂
-- neutrophils w/ small, pleomorphic g-neg bacilli suggesting H. influenzae
- H. infl. is fastidious requires enriched media, 35-37℃, 5-10% CO₂
g-pos cocci suggestive of Streptococcus
-- Streptococcus is g-pos cocci in pairs or chains (esp. in fluid)
-- Staph is also g-pos but usually singly, pairs, clusters, short chains
A vaginal/rectal swab is collected from a pregnant pt to screen for grp B Strep. What is the best medium to use for specimen inoculation?
-- at 35-37 wks, a single swab is inserted in vagina then rectum for detection of gBS
the cefazolin result should be changed to resistant since oxacillin result is resistant
-- oxacillin res. staph are res. to ALL beta-lactam agents, inhibitors, and carbapenems
To control the autoclave, a vial of Bacillus stearothermophilus is autoclaved and should then be:
incubated at 56℃
-- since it only grows at that temp, it's a good measure of autoclave effectiveness
In a QC procedure on a new batch of Mueller-Hinton plates using a stock culture of S. aureus, all disk zones are too small. Most likely reasons:
org inoculum is too high; plates poured too thick; potency of antibiotic disks too low
indole-neg : E coli & Proteus mirabilis
-- E coli is indole pos, Proteus neg
-- all others listed are pos for tests (no neg ctrl)
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