NAVLE (North American Veterinary Licensing Examination) · USA / Canada · International Council for Veterinary Assessment (ICVA); scored by NBME, delivered by Prometric
Original practice questions written to the published syllabus · not past papersHow bacteria and fungi are built, grown, identified and killed, and how bacteria become resistant to antimicrobials.
In the exams: ICAR AICE-JRF core group 06; ICAR AIEEA-PG 13 (Microbiology); PRC Microbiology & Public Health 14%; China microbiology and immunology 35 (its largest single component); TNPSC Micro/VPH/Preventive Medicine 30
NAVLE, BCSE, RCVS SME, Australasian Veterinary Examination and similar licensing examinations
Tested through clinical scenarios: choosing and handling the specimen, reading a Gram stain or cytology, interpreting culture growth as cause or contaminant, reading a susceptibility report against breakpoints, choosing a disinfectant for a pathogen such as parvovirus, and prudent antimicrobial use.
How our questions for NAVLE spread across the units of General Veterinary Microbiology. Difficulty: 6 easy, 28 medium, 7 hard.
| Bacterial identification | 7 | |
| Disinfection | 7 | |
| Mechanisms of antimicrobial resistance | 7 | |
| Culture methods | 6 | |
| General mycology | 5 | |
| Bacterial growth | 4 | |
| Bacterial structure | 2 | |
| Sterilisation | 2 | |
| Bacterial classification | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
When collecting quarter milk samples for mastitis culture, the recommended order is to:
B. Disinfect teat ends from the far teats, then sample starting with the near teats
Scrubbing far teats first and sampling near teats first avoids reaching across, and contaminating, teats already cleaned. Foremilk is discarded, not sampled, and teat ends are scrubbed with 70% alcohol until the swab is clean.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
Ethylene oxide is used to sterilise heat-sensitive instruments such as some plastic endoscopes. Its main practical drawback is that:
B. It is toxic and carcinogenic, so items need a long aeration period to remove residues
Ethylene oxide is an alkylating agent that kills spores at low temperature (about 37-63 degrees C) and penetrates packaging, but it is flammable, toxic and carcinogenic. Items must be aerated before use.
Further reading: Rutala, Weber and HICPAC, CDC Guideline for Disinfection and Sterilization in Healthcare Facilities
Under the Spaulding classification, a flexible endoscope that contacts intact mucous membranes should, at minimum, receive:
B. High-level disinfection
Critical items (entering sterile tissue or vessels) must be sterile; semi-critical items (contacting mucous membranes or non-intact skin), such as endoscopes, need at least high-level disinfection; non-critical items (intact skin) need low or intermediate level. Cleaning always comes first.
Further reading: Rutala, Weber and HICPAC, CDC Guideline for Disinfection and Sterilization in Healthcare Facilities
Household bleach containing 5.25% sodium hypochlorite is to be diluted to give 2 litres of a solution with 1000 ppm available chlorine. How much bleach is needed (to the nearest mL)?
A. About 38 mL, made up to 2 litres with water
1000 ppm = 1000/10,000 = 0.1%. V1 = C2V2/C1 = 0.1 x 2000 / 5.25 = 38.1 mL, about 38 mL. Treating 1000 ppm as 1% gives about 381 mL; 105 mL is C1 x V2 / 100 with the terms mixed up; about 4 mL treats 1000 ppm as 0.01%. Actual strength of bleach varies by product and falls with storage, so check the label.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease, 2nd ed.
An E. coli isolate from a calf is resistant to third-generation cephalosporins, and this resistance is reversed by clavulanic acid. The most likely mechanism is:
C. An extended-spectrum beta-lactamase (ESBL), such as a CTX-M enzyme
ESBLs hydrolyse extended-spectrum cephalosporins but are inhibited by clavulanate; CTX-M types are the commonest worldwide in animals and people. AmpC enzymes also hydrolyse these drugs but are poorly inhibited by clavulanate, which is the distinguishing point.
Further reading: CLSI VET01/VET01S; WOAH Terrestrial Manual ch. 2.1.1; Giguere et al., Antimicrobial Therapy in Veterinary Medicine, 5th ed.
A Staphylococcus isolate is erythromycin-resistant and appears clindamycin-susceptible, but the clindamycin zone is flattened (D-shaped) next to an erythromycin disk. How should clindamycin be reported and why?
A. Resistant, because erythromycin induces an erm methylase giving MLSB resistance
The D-test detects inducible MLSB resistance: erm genes methylate 23S rRNA, blocking binding of macrolides, lincosamides and streptogramin B. Clindamycin can fail during therapy when resistance is induced, so the result is reported as resistant. mecA is unrelated.
Further reading: CLSI VET01/VET01S; WOAH Terrestrial Manual ch. 2.1.1; Giguere et al., Antimicrobial Therapy in Veterinary Medicine, 5th ed.
In the disk diffusion (Kirby-Bauer) test on Mueller-Hinton agar, the zone of inhibition around a disk is:
C. Inversely related to the MIC: larger zones mean lower MICs
The drug diffuses outward in a concentration gradient; growth stops where the concentration exceeds the MIC, so a more susceptible organism gives a wider zone. Inoculum (0.5 McFarland), agar depth and incubation are standardised because they all change zone size.
Further reading: CLSI VET01/VET01S; WOAH Terrestrial Manual ch. 2.1.1; Giguere et al., Antimicrobial Therapy in Veterinary Medicine, 5th ed.
Ten here, 41 in the app. The Laisha app has every practice question we have written to NAVLE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
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