Question 1

The laboratory autoclave is used to decontaminate culture plates and broths before disposal. Every load this month has carried indicator tape that darkened correctly, and the cycle printouts show the set temperature and hold time were reached. During an accreditation visit the assessor asks what evidence the laboratory holds that those loads were genuinely being decontaminated. Which routine check provides it?

Accepted Answer

A weekly Geobacillus spore strip run in a load — A biological indicator carries spores of Geobacillus stearothermophilus, chosen because they resist moist heat far better than anything in the waste itself. The strip is processed inside a representative load and then incubated; no growth is direct evidence that conditions reached inside the load were lethal, not merely that heat was applied to the chamber. Weekly is the usual interval, and a growth-positive strip takes the autoclave out of service until the cause is found.

Question 2

Quantitative urine cultures in a community laboratory are plated with a reusable 1 µL wire loop that has been in daily use for eight months. The colony counts have all looked plausible and none has been questioned. Which practice keeps those counts defensible?

Accepted Answer

Check the loop's delivered volume regularly — A wire loop bends in handling and thins with repeated flaming, so the volume it actually delivers drifts away from the nominal 1 µL. Because the colony count is divided by that volume — multiplied by its reciprocal — to report organisms per litre, a drifted loop shifts every urine result in the same direction, often across the threshold that separates significant growth from contamination. Verifying delivered volume periodically — gravimetrically, or with a dye and spectrophotometer — is what keeps the counts defensible, and the check is recorded.

Question 3

For two consecutive mornings the Neisseria gonorrhoeae control strain fails to grow on chocolate agar incubated in one incubator, while the Escherichia coli control on MacConkey agar in the same chamber grows normally. A plate from a fresh lot of chocolate agar fails in the same way, the chamber display reads 35.4 °C, and the control strain grows well when a plate is set up in a candle extinction jar. What is the most likely fault?

Accepted Answer

The carbon dioxide regulator has failed — The laboratory's own controls have already narrowed this: the same strain grows once a plate is given carbon dioxide in a candle jar, and an organism with no such requirement grows untouched in the chamber. Neisseria gonorrhoeae is capnophilic, so it is the first thing to fail when an empty cylinder, a closed valve or a failed regulator stops gas reaching the chamber. The next step is to check the supply and regulator and confirm the chamber's carbon dioxide reading against an independent measurement.

Question 4

A deep wound aspirate is set up on the anaerobic bench and incubated in a jar with a gas-generating sachet. After 48 hours the anaerobic blood agar plate carries only a facultative organism that also grew on the aerobic set, and the methylene blue indicator strip inside the jar is blue. What is the correct interpretation?

Accepted Answer

Anaerobiosis failed; set the culture up again — A methylene blue indicator is colourless once the atmosphere is anaerobic and turns blue on contact with oxygen, so a blue strip at the end of incubation says the jar either never became anaerobic or did not stay that way. The facultative isolate grew because it never needed anaerobic conditions, and any obligate anaerobe present would have been suppressed or killed. The culture is repeated from retained material with a fresh sachet, a checked catalyst and a sound seal, and the failure is logged.

Question 5

A Gram-stained smear was photographed through the microscope camera so that a colleague at the regional site could review the Gram reaction. Because the value of this image rests on the colour of the organisms, which step matters most at the point of capture?

Accepted Answer

Set white balance on a blank field first — Gram interpretation rests on hue, and microscope lamps run warm, so an uncorrected camera records violet organisms as reddish and invites a false Gram-negative call at the far end. Setting white balance on a blank, illuminated part of the slide at the working light level tells the camera what neutral looks like under that lamp, so the captured colours match what is seen down the eyepieces. It takes seconds, and it is done before capture rather than corrected afterwards.

Question 6

At 02:00 a technologist wants advice from the on-call microbiologist about an unusual Gram film from a positive blood culture. The quickest route is to photograph the field on a personal phone and send the picture by text message. Which action meets the laboratory's obligations for images of patient material?

Accepted Answer

Capture and share it on the laboratory system — A photograph of patient material is patient information, and a personal device puts it outside the laboratory's control — synchronised to consumer cloud storage, retained indefinitely, and unconnected to the case it belongs to. Capturing on the microscope camera or another laboratory device lets the image be filed against the accession, shared through an approved route to the microbiologist, and retained then disposed of under the laboratory's own schedule. That chain of custody is what the SOP and privacy legislation both expect.

Equipment and Resources

Holding instruments in a state you can trust

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