Monthly Archives: May 2013

“Damage Limitation…”

Bacteriology laboratories vary hugely in the number of antibiotics they release to the clinicians…

Some laboratories release up to 20 antibiotics on every reported isolate (particularly those ones with Vitek/Phoenix systems)

In contrast, some laboratories release as few antibiotics as possible to the requestors.

Personally I am very much in the latter camp. I strongly believe that it is the laboratory’s responsibility to guide the clinicians as much as possible in their antibiotic choices in order that the patient gets the most appropriate therapy and the unnecessary use of broad spectrum antibiotics is minimised.

For example:

i) A coagulase negative staphylococcus isolated from one bottle of a blood culture set: In the absence of prosthetic material or severe immunocompromise this is almost certainly going to be a contaminant. It should thus be reported as such and no antibiotics released.

ii) A Staphylococcus aureus isolated from a blood culture: Unless there is a history of allergy this should be reported with flucloxacillin alone (if it is susceptible to this). Flucloxacillin (or whatever your equivalent is (cloxacillin, dicloxacillin) is well established as the optimal treatment for Staphylococcus aureus bacteraemia. If you start releasing antibiotics such as erythromycin, ciprofloxacin etc on all such isolates you can be sure that somewhere along the line a clinician will elect to use one of these drugs. (possibly due to lack of knowledge or interest in microbiology).

iii) A Pseudomonas aeruginosa isolated from a chronic leg ulcer. In the vast majority of cases this will be colonising only. If the laboratory starts releasing ciprofloxacin (and other antibiotics) for all such isolates, then there will inevitably be a lot of inappropriate quinolone use.

iv) An amoxycillin susceptible E.coli isolate in a blood culture. Why report meropenem when it is amoxycillin susceptible?

These are only a few examples amongst many…

I strongly believe that the laboratory has a role in “focusing” the anti-microbial prescribing of clinicians. It is also important to note there will be the odd occasion where a coagulase negative staphylococcus bacteraemia does need treated, where a Staph. aureus bacteraemia does need something apart from flucloxacillin, where a pseudomonas is causing problem in a leg ulcer. In these cases the laboratory should ensure it is easily accessible to the clinician so that further antibiotics can be tested/reported.

To those laboratories that insist on reporting all antibiotics on everything, I would encourage that you review this practice. You may find that by careful and appropriate restriction of antimicrobial reporting, the clinicians (and patients) will eventually thank you for it….


Ssh… it’s a secret!

For various reasons, Microbiology Laboratories have generally been very protective of their particular methodologies, and methods manuals are often regarded by the laboratory as “intellectual property”. Each laboratory thinks that their way is the best way, possibly even the only way to do things. Laboratories are often reluctant to release any of their “trade secrets” to other, potentially competing laboratories.

However in the internet age, secrets are harder and harder to keep… The concept of intellectual property is slowly but surely disappearing. Protectionism is slowly being replaced by sharing and connectivity.

After I leave NZ in 6 weeks time I plan on doing some locum work in both London and Paris. Over the next few months I am looking forward to seeing how different laboratories (public and private, community and hospital) operate and what different methodologies they use. I will certainly be sharing my experience with them, in the hope that they will not hide any secrets from me…


I think it might be a while though before microbiology methods manuals from laboratories are freely available for public viewing on the internet. That really would be radical!

Microbiology Picture Quiz Number 6

Have a look at this agar plate below and answer the questions: (for bacteriologists only)



1) What is this test called and why?

2) Given that the horizontal streak is Staphylococcus aureus, what organism is likely to be represented by the “arrow” pointing towards it?

3) What other bacterium can cause a similar phenomenen?

4) How useful is this test likely to be in the future?


Click here for the answers with brief explanations