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Microbiology

Preanalytical and Susceptibility testing

QuestionAnswer
Proper media for culture of a urethral discharge from a man include: chocolate and modified Thayer-Martin agar
A sheep blood agar plate inoculated with 0.001mL of urine grows 70 colonies of Staphylococcus aureus. How many colony forming units per mL of urine should be reported? 70,000
The lowest concentration of antibiotic that inhibits growth of a test organism is the? Minimum inhibitory concentration
Which clean catch colony count indicates the patient likely has a urinary tract infection? 1000 CFU/ML
The steam autoclave method of sterilization: uses 15 lbs of pressure for 15 minutes
The expected colony count in a suprapubic urine from a healthy individual is? 0 CFU/mL
An aspirate of a deep would was plated on blood agar plates and incubated aerobically and anaerobically. At 24 hours there was growth on both plates. This indicated that the organism is? facultative anaerobe
A penicillin-resistant Neisseria gonorrhoeae produces? beta-lactamase
Which selective medium is used for the isolation of gram-positive microorganisms? Columbia CNA with 5% sheep blood
The MOST sensitive substrate for the detection of beta-lactamases is: nitrocefin
An Enterococcus isolated from multiple blood cultures in a patient endocarditis should be: screened for high level aminoglycoside resistance
In the Kirby-Bauer disc diffusion susceptibility test, which variable is critical when testing Pseudomonas species for antibiotic susceptibility to aminoglycosides ? cation content of media
The procedure that as sues the MOST accurate detection of mecA-mediacted oxacillin resistance in routine broth micro dilution susceptibility testing against S. aureus is: use of cefoxitin for testing
Susceptibility testing performed on QC organisms using a new media lot # yielded zone sizes that were too large for all antibiotics tested. What best explains the unacceptable zone sizes? The depth of the media was too thin
3 sets of blood cultures were obtained from an adult patient with fever and suspected endocarditis. The aerobic bottle of one set had growth of Staphylococcus epidermidis at 5 days of incubation. This indicates that: the organism is MOST likely a contaminant
In order to isolate Campylobacter coli/jejuni, the fecal specimen should be: inoculated onto selective plating media and incubated in reduced oxygen with added CO2 at 42C
Which type of microscope would be MOST useful in examining viruses and the structure of microbial cells? electron
After satisfactory performance of daily disk diffusion susceptibility QC is documented, the frequency of QC can be reduced to: every week
In disk diffusion susceptibility testing, as an antimicrobial agent diffuses away from the disk, the concentration of antibiotic is: decreased
The MOST common cause for failure of a GasPak anaerobic jar to establish an adequate environment for anaerobic incubation is: catalysts that have become inactivated after repeated use
What is the MOST appropriate method for collecting a urine specimen from a patient with an indwelling catheter? aspirated urine aseptically form the catheter tubing
A liquid fecal specimen from a 3 month-old infant is submitted for microbiological examination. In addition to culture on routine media for Salmonella and Shigella, this specimen should be routinely: examined for the presence of Campylobacter sp.
CSF from a febrile 25 yr old man w/possible meningitis is rushed to the lab for a stat Gram stain and culture. While performing the GS, the tech spills MOST of the specimen. Smear shows many neutrophils and no microorgs. Which plate should be inoculated? chocolate agar plate
Upon review of a sputum Gram stain, the tech notes that the nuclei of all of the neutrophils present in the smear are staining dark blue. The best explanation for this finding is: the slide was inadequately decolorized with acetone/alcohol
When performing a Kovac indole test, the substrate must contain: tryptophan
The ONPG test allows organisms to be classified as a lactose fermenter by testing for: beta-galactosidase
Sodium bicarbonate and sodium citrate are components of what: JEMBEC system
Chocolate agar base containing vancomycin, colistin, anisomycin, and trimethoprim is also known as: Martin Lewis agar
A medium that aids in the presumptive identification of organisms based on their appearance on the medium is called? differential
SPS is used as an anticoagulant for blood cultures because it: inactivates neutrophils and components of serum complement
When evaluating a new susceptibility testing system, if the new system characterizes a susceptible isolate as resistant, this is termed a: major error
What method id inadequate for the detection of vancomycin-intermediate S. aureus? disk diffusion
In a disk diffusion susceptibility test, what can result if disks are placed on the inoculated media and left at room temperature an hour before incubation? zones of larger diameter would result
Which factors would make an organism appear to be more resistant on a disk diffusion susceptibility test? too many organisms in the inoculum
First generation cephalosporins can be adequately represented by: cephalothin
An antibiotic that inhibits cell wall synthesis is: penicillin
Which antibiotics would routinely be tested and reported for isolates of Pseudomonas aeruginosa gentamicin
Which organism must be incubated in a microaerophilic environment for optimal recovery of the organism? Campylobacter jejuni
Diagnosis of typhoid fever can be confirmed best by culture of: blood
Vibrio parahaemolyticus can be isolated best from feces on: thiosulfate citrate bile salts (TCBS) agar
Which media can be used to culture Campylobacter jejune? Skirrow medium
Tests for beta-lactamase production in Haemophilus influenzae: should be performed on all blood and CSF isolates
Media used to support growth of Legionella pneumophila should contain which additives? charcoal and yeast extract
The best medium for culture of Bordetella pertussis is: Regan-Lowe agar
The best medium for culture of Francisella tularensis is: cystine glucose blood agar
The MOST rapid method for detection of Francisella tularensis is: polymerase chain reaction
When processing throat swabs for a group A strep culture, the medium of choice is: sheep blood agar
The ability to detect oxacillin-resistant Staphylococcus aureus may be enhanced by: using Mueller-Hinton broth with 2% NaCl
The optimal wound specimen for culture of anaerobic organisms should be: a syringe filled with pus, obtained before administration of antibiotics
A 21 yr old patient presents with pharyngitis. A throat swab is collected and submitted for anaerobic culture. This specimen should be: rejected as unacceptable
Anaerobic susceptibility testing is helpful in the management of patients with: synovial infections
An antibiotic used to suppress or kill contaminating fungi in media is: cycloheximide
Production of beta-lactmase is inducible in which organism: Staphylococcus aureus
A tech is reading a GS from a CSF and observes many neutrophils and lancet-shaped gram-positive diplococci. Which chemistry and hematology CSF results would MOST likely be seen with this infection: WBC: increased Glucose: decreased Protein: increased
Which tests is used to monitor bactericidal activity during antimicrobial therapy in cases of endocarditis? Schlichter
Quality control results for disk diffusion susceptibility tests yield the following results: amino glycoside zones too small and penicillin zones too large. This is MOST likely due to: the pH of Mueller-Hinton agar being too low
When using a control strain of Staph aureus, the tech notices that the zone around the oxacillin disk is too small. What is the MOST likely explanation: use of outdated oxacillin disks
In the disk diffusion method of determining antibiotic susceptibility, the size of the inhibition zone used to indicate susceptibility has been determined by: correlating the zone size with minimum inhibitory concentrations
Which organism may be mistaken for Neisseria gonorrhoeae in Gram stained smears of uterine cervix exudates? Moraxella osloensis
A 73 yr old man diagnosed as having pneumococcal meningitis is not responding to his penicillin therapy. Which tests should be performed on the isolate to best determine the susceptibility to penicillin? oxacillin disk diffusion
Salmonella enteritidis is isolated from multiple blood bultures in a patient with fever. Susceptibility results are as follows: ampicillin-S, ceftriaxone-S, ciprofloxacin-S, trimethoprim/sulfamethoxazole-R. What is the next best step? test the isolate against nalidixic acid and if resistant report the ciprofloxacin as susceptible
Which antimicrobials would be inappropriate to report on an E.coli isolated from a wound culture? nitrofurantoin
Which combination is useful for confirming the presence of extended spectrum beta-lactamases in E. coli? ceftazidime + clavulanic acid
Enzymatic drug modification is a mechanism of resistance for which antimicrobial? gentamicin
Which is the MOST important variable in the recovery of organisms in patients with bacteremia? the volume of blood cultured
A vaginal/rectal swab is collected from a pregnant patient to screen for group B strep. What is the best medium to use for specimen inoculation? LIM broth
To quality control the autoclave, a vial of Bacillus stearothermophilus is autoclaved and should then be: incubated at 56C
In a quality control procedure on a new batch of Mueller-HInton plates using a stock culture of Staph aureus (ATCC 25923), all the disk zone sizes are too small. The MOST likely reason for this: bacterial suspension was not diluted to the proper concentration
Created by: emery87