Tips for Microbiology Scientists. (Part I)

Tips for Microbiology Scientists working on the Bacteriology Culture Benches. (Part I)

1)      The clinical value of a result is (in general) inversely proportional to the number of days spent generating it.

In the vast majority of cases, once you are 4 or 5 days down the line from the sample being taken, the clinical value of the result starts to wane. It is at this point that one must start to ask. “What difference is it going to make to the patient to get a definitive ID on this organism” or “Do I really need to know what the penicillin MIC on this difficult to grow Coryne is?”. Find out if the patient is still unwell, whether they have been discharged etc etc. Often the answer is that the patient has long since been treated and discharged and your time (and the laboratory’s resources) could have been better spent on other work. This is not always the case of course, but exactly this scenario occurs far too frequently to be ignored.

2)      The clinical value of a result is inversely proportional to the number of different organism types present in this sample.

Once 3 different organism types are found in a sample the clinical significance of each individual organism starts to decrease. Once you have 5 or 6 it is almost impossible to give any meaningful results from the sample. If you have such a sample, focus on the organisms that are the likely pathogens, and just mention the others. With multiple organism samples, it is easy to fall into the trap above and start spending several days working them all through. This is very important when you see what looks like enteric flora on the plates. In my opinion this should be reported as enteric flora. There are very few occasions where it is actually necessary to work up individual organisms in “enteric flora”.

With both these first two points I must emphasize, that I personally am happy for an “incomplete result” to be released, even as a final report. If it is taking too long to identify an organism that is unlikely to be pathogenic in the first place, don’t identify it!

3)      Once you have clinically useful lab information, release it to the clinicians.

This to some extent depends on how your laboratory information system is set up. In some cases your interim work will be released to the clinicians anyway. For some labs you will need to actively release the information. The point is, don’t hold useful information back just so that you can release the “perfect result” in a couple of days’ time. Trust me, the patient will not thank you for this. If you have information which suggests the likely ID but are awaiting confirmation, then often it is worthwhile releasing this as well. For example, If you have a CoNS from a blood culture, which is latex negative and you are awaiting a tube coagulase, then it is ok to add a comment to the interim result “Staphylococcal species. Likely to be a CoNS on the basis of current results. Confirmation awaited.” In most cases you will be right and possibly saved the patient unnecessary antibiotics. On the occasional case that you are wrong, you have not put out any misleading information on your report.

4)      Focus your time on the important samples.

There is a large range of samples which are received into the lab, anything from blood cultures/sterile site specimens on ICU patients to superficial wound swabs from chronic leg ulcers. Focus your time and efforts on samples that are likely to make a significant clinical difference. I would estimate that less than 10% of microbiology samples coming through the lab impact on a patients treatment, and of that 10 % less than half will have a significant, potentially life saving impact on treatment. (You might not want to hear that, but I believe it to be true!). Without ignoring the rest of the work completely, focus your time and energy on sterile site samples, blood cultures, samples from CF sufferers, samples from patients in ICU or not responding to treatment.

5)      Know when something is odd/does not look right.

This is to some extent common sense, but also boils down to experience and a degree of intuition. Every bench will have it’s bread and butter work but every so often something will crop up which does not fit; ie. An unusual organism, or an unusual antibiogram for a common organism. Stop and reflect when this happens. Is it laboratory error, or is this something genuine? Ask for help if necessary, regardless of your seniority This is often where the interesting stuff in microbiology lies, and the art of spotting the odd and unusual is one that should be coveted by microbiology scientists and clinical microbiologists alike.


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