A 38-year-old man near Al Ain who drinks raw camel milk has had fever, night sweats, weight loss and back pain for 7 weeks. Two weeks ago a clinic gave him a 5-day course of oral antibiotics. Two blood culture sets, incubated for 21 days, are negative. The Rose Bengal test is positive and the standard tube agglutination titer is 1:320 (significant in this region at 1:160 or more). His physician asks the laboratory to try to isolate the organism to confirm the diagnosis. Which specimen is most likely to grow it, and how should it be handled?

Bone marrow aspirate, worked in a safety cabinet

Bone marrow aspirate, worked on the open bench

Midstream urine, worked in a safety cabinet

New blood cultures, worked in a safety cabinet

A blood culture grows tiny gram-negative coccobacilli after 4 days. They do not grow on MacConkey agar, are oxidase and catalase positive and non-motile, and turn a urea slant positive within 2 hours. Which result most supports Brucella rather than Pasteurella multocida?

The absence of growth on MacConkey agar

Coxiella burnetii, the cause of Q fever in people who work with livestock, is diagnosed in the routine laboratory by:

Serology or nucleic acid testing, not culture

Culture on chocolate agar in carbon dioxide

Culture in thioglycollate broth

An automated panel identifies a tiny, slow-growing gram-negative coccobacillus from the blood of a man who drinks raw camel milk as Ochrobactrum anthropi. What should the laboratory do?

Treat it as possible Brucella and refer it

Report the panel identification

Report it as a skin contaminant

Repeat the panel with a heavier inoculum

How should blood cultures from a patient with suspected brucellosis be handled?

Held beyond the routine period, and subcultured in a cabinet

Frozen until a serology result is available

Reported negative after 48 hours, as with routine culture sets

Vented to give the organism extra oxygen

Brucella and zoonotic pathogens

10 DOH Abu Dhabi (HAAD) lab licensing practice questions on Brucella and zoonotic pathogens, part of Microbiology. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 38-year-old man near Al Ain who drinks raw camel milk has had fever, night sweats, weight loss and back pain for 7 weeks. Two weeks ago a clinic gave him a 5-day course of oral antibiotics. Two blood culture sets, incubated for 21 days, are negative. The Rose Bengal test is positive and the standard tube agglutination titer is 1:320 (significant in this region at 1:160 or more). His physician asks the laboratory to try to isolate the organism to confirm the diagnosis. Which specimen is most likely to grow it, and how should it be handled?
1. ABone marrow aspirate, worked on the open bench
2. BMidstream urine, worked in a safety cabinet
3. CBone marrow aspirate, worked in a safety cabinet
4. DNew blood cultures, worked in a safety cabinet
Show answerHide answer
Answer: C · Bone marrow aspirate, worked in a safety cabinet
Raw camel milk, a long fever with back pain and a significant agglutination titer point to brucellosis, most often caused by Brucella melitensis. Brucella survives inside macrophages of the bone marrow, liver and spleen, so bone marrow culture is more sensitive than blood culture, especially in long-standing infection and after antibiotics. Brucella is one of the commonest causes of laboratory-acquired infection, so all cultures from such a patient must be handled in a class II biosafety cabinet with BSL-3 practices, and staff should be warned. Repeat blood cultures after antibiotics are less likely to grow it, and urine culture has a low yield.
- A: Brucella spreads to laboratory staff by aerosol, so open-bench work is never acceptable.
- B: Urine culture rarely grows Brucella and is not the specimen of choice.
- D: Blood cultures are less sensitive than bone marrow, especially after antibiotics.
Question 2 · Hard
A blood culture grows tiny gram-negative coccobacilli after 4 days. They do not grow on MacConkey agar, are oxidase and catalase positive and non-motile, and turn a urea slant positive within 2 hours. Which result most supports Brucella rather than Pasteurella multocida?
1. AThe oxidase reaction
2. BThe absence of growth on MacConkey agar
3. CThe 4-day time to growth
4. DThe urease reaction
Show answerHide answer
Answer: D · The urease reaction
Both organisms are small, oxidase-positive gram-negative rods that fail to grow on MacConkey agar, so those features do not separate them. Brucella is urease positive, usually within 2 hours, while Pasteurella multocida is urease negative and indole positive. Pasteurella also grows well overnight on blood agar, whereas Brucella is slow, and a slow urease-positive isolate should go straight into a biosafety cabinet.
- A: Both organisms are oxidase positive.
- B: Neither organism grows on MacConkey agar.
- C: Time to growth is suggestive but overlaps, and some Brucella isolates flag earlier.
Question 3 · Medium
Coxiella burnetii, the cause of Q fever in people who work with livestock, is diagnosed in the routine laboratory by:
1. ACulture on chocolate agar in carbon dioxide
2. BA rapid urease test on blood
3. CCulture in thioglycollate broth
4. DSerology or nucleic acid testing, not culture
Show answerHide answer
Answer: D · Serology or nucleic acid testing, not culture
Coxiella burnetii is an obligate intracellular organism that does not grow on ordinary media; isolation needs cell culture in a containment laboratory and is not attempted in a routine laboratory. Phase I and phase II antibodies by immunofluorescence are the mainstay, with nucleic acid testing useful in the first two weeks before antibodies appear. The organism is highly infectious by aerosol, so suspicion should be flagged on the request.
- A: It cannot be grown on chocolate agar or any other routine plate.
- B: Urease testing has no role for this organism.
- C: Thioglycollate broth does not support intracellular organisms.
Question 4 · Medium
An automated panel identifies a tiny, slow-growing gram-negative coccobacillus from the blood of a man who drinks raw camel milk as Ochrobactrum anthropi. What should the laboratory do?
1. AReport the panel identification
2. BReport it as a skin contaminant
3. CRepeat the panel with a heavier inoculum
4. DTreat it as possible Brucella and refer it
Show answerHide answer
Answer: D · Treat it as possible Brucella and refer it
Commercial biochemical panels and some mass spectrometry libraries either lack Brucella or are not validated for it, and misidentification as Ochrobactrum, Psychrobacter or Moraxella is well described. A small, slow-growing, non-lactose-fermenting coccobacillus that is oxidase and catalase positive and rapidly urease positive, in a patient with raw milk or animal contact, should be contained and referred. Further bench work outside a cabinet risks exposing staff.
- A: Reporting the panel name would miss a notifiable and hazardous organism.
- B: Brucella in a blood culture is never dismissed as a contaminant.
- C: Repeating the panel keeps the isolate on the bench and does not solve the problem.
Question 5 · Medium
How should blood cultures from a patient with suspected brucellosis be handled?
1. AFrozen until a serology result is available
2. BHeld beyond the routine period, and subcultured in a cabinet
3. CReported negative after 48 hours, as with routine culture sets
4. DVented to give the organism extra oxygen
Show answerHide answer
Answer: B · Held beyond the routine period, and subcultured in a cabinet
Brucella grows slowly; most isolates in modern continuous-monitoring systems flag within 7 days, but incubation is extended when brucellosis is suspected, and terminal subculture is worthwhile. Every manipulation is done inside a biosafety cabinet, so the request should carry the clinical suspicion. Bone marrow culture gives a higher yield than blood in long-standing or previously treated infection.
- A: Freezing the bottles would kill the organism and waste the specimen.
- C: Forty-eight hours is far too short for this slow-growing organism.
- D: Venting creates aerosols and does not help growth.
Question 6 · Hard
After an isolate is identified as Brucella melitensis, exposures are graded. Which member of staff has had a high-risk exposure?
1. AThe technologist who loaded the bottle into the analyser
2. BThe technologist who read the Gram-stained smear
3. CThe clerk who entered the result in the computer
4. DThe technologist who vortexed and spotted the isolate openly
Answer and explanation in LearnFree account
Question 7 · Easy
Which Brucella species is most often acquired from unpasteurised goat and camel milk?
1. ABrucella melitensis
2. BBrucella abortus
3. CBrucella canis
4. DBrucella ovis
Answer and explanation in LearnFree account
Question 8 · Medium
Which laboratory activity has caused most laboratory-acquired Brucella infections?
1. APipetting with a mechanical aid
2. BWorking cultures on the open bench
3. CReading fixed Gram-stained smears
4. DCentrifuging capped serum tubes
Answer and explanation in LearnFree account
Question 9 · Easy
An isolate that may be Brucella must be worked:
1. AOn the open bench, wearing gloves and a fluid-resistant gown
2. BIn a class II biosafety cabinet, with BSL-3 practices
3. CIn a chemical fume hood with the sash down
4. DIn a laminar flow clean air bench
Answer and explanation in LearnFree account
Question 10 · Hard
A patient who drank unpasteurized camel milk has small gram-negative coccobacilli in a blood culture. They are oxidase positive and rapidly urease positive. What is the most likely organism, and what precaution is needed?
1. AHaemophilus influenzae, on the open bench
2. BBordetella pertussis, no special precautions
3. CAcinetobacter baumannii, contact precautions only
4. DBrucella, handled in a biosafety cabinet
Answer and explanation in LearnFree account

Brucella and zoonotic pathogens

A blood culture grows tiny gram-negative coccobacilli after 4 days. They do not grow on MacConkey agar, are oxidase and catalase positive and non-motile, and turn a urea slant positive within 2 hours. Which result most supports Brucella rather than Pasteurella multocida?

Coxiella burnetii, the cause of Q fever in people who work with livestock, is diagnosed in the routine laboratory by:

An automated panel identifies a tiny, slow-growing gram-negative coccobacillus from the blood of a man who drinks raw camel milk as Ochrobactrum anthropi. What should the laboratory do?

How should blood cultures from a patient with suspected brucellosis be handled?

After an isolate is identified as Brucella melitensis, exposures are graded. Which member of staff has had a high-risk exposure?

Which Brucella species is most often acquired from unpasteurised goat and camel milk?

Which laboratory activity has caused most laboratory-acquired Brucella infections?

An isolate that may be Brucella must be worked:

A patient who drank unpasteurized camel milk has small gram-negative coccobacilli in a blood culture. They are oxidase positive and rapidly urease positive. What is the most likely organism, and what precaution is needed?