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Microbiology
Preanalytical and Susceptibility testing
| Question | Answer |
|---|---|
| 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
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