Monthly Archives: March 2013

“Susceptibility testing for Staphylococcus aureus in community patients. Just in case..?”

Antimicrobial Resistance, Confessions of a Microbiologist, ,

You have isolated a Staphylococcus aureus from a superficial wound swab from a community patient. What antibiotics do you need to test against?

120px-Staphylococcus_aureus_(AB_Test)

If you are fortunate enough to have Automated Susceptibility testing (Vitek, Phoenix etc) you may test the isolate against a panel of 20 different Gram positive antibiotics at a not unsignificant cost. You will also be testing against a lot of antibiotics that are never going to be used to treat that patient.

If you perform anti-microbial susceptibility testing mainly by disc diffusion on agar plate, then you will likely test the Staphylococcus aureus against 6 or 7 antibiotics of your choosing. Again, in the vast majority of patients, some of these antibiotics will neither be reported nor used.

In the laboratory I work in, we cut the number of antibiotics routinely tested for a Staphylococcus aureus isolate from six to three, of which we routinely report two of them to the clinicians. In the three years that we have had this policy we have not had one negative comment from our laboratory users. (On occasion of course we do test more, ie MRSA isolate, patient with multiple allergies.)

It made me realise just how much susceptibility testing that we do on a “Just in Case” basis, not only for Staphylococcus aureus, but also for a multitude of other micr-organisms also.

It will be very interesting if MALDI-TOF technology becomes proficient at identifying MRSA in the future. If this happens, then (if no history of allergy on the request form), one could simply put out a report saying: “Staphylococcus aureus isolated, (not MRSA). Susceptibilities on request.”

A radical, but ultimately reasonable and cost-effective approach, which I am sure would be accepted by laboratory users…

Michael

“The Bunsen Burner: Keeping the flame burning for the laboratory”

Confessions of a Microbiologist

69px-Bunsen_burnerMuch like the Gram stain, a discovery that stands the test of time, usually has enduring qualities to it. The Bunsen Burner was invented in 1854. It was named after and commissioned by Robert Bunsen, a German chemist working at Heidelberg University, but was probably designed by his colleague Peter Desaga. The “Bunsen burner” was really just an improvement on other laboratory gas burners that were already in existence, including one invented by Michael Faraday. Although Robert Bunsen will always be associated with the Bunsen Burner, he was also an outstanding chemist and was responsible for the discovery of the elements caesium and rubidium, mainly through his pioneering work on spectro-chemical analysis.

 

The secret of the Bunsen Burner is it’s ability to mix the fuel (methane or similar) with oxygen, before the mixture is ignited. This is done by using an inlet valve at the bottom of the burner column which draws in air by the Venturi effect. The mixture is then ignited at the top of the column. The adjustable valve (collar) at the bottom dictates how much oxygen gets into the mixture. With a closed valve very little oxygen gets in and a smoky yellow “low temperature” flame is produced. With the valve fully open, a hot, almost colourless, roaring flame results.

I know that a lot of microbiology (bacteriology) laboratories have now got rid of the Bunsen Burner, in favour of the rather dull disposable plastic loops. I know there are risks with Bunsens (burns, fire etc..) but for me I still retain an affinity for the Bunsen, especially when it roars…

Michael

p.s. When I was 11, I received for Christmas a laboratory standard Bunsen Burner, a bottle of concentrated sulphuric acid and various other exotic chemicals. I enjoyed using these to carry out all sorts of dangerous experiments in the controlled environment of the bathroom cupboard!

Santa doesn’t make toys like he used to any more….

Carbapenem Usage Reduction Bundle (CURB)

Antimicrobial Resistance, , ,

For the majority of healthcare locations worldwide, the “top of the ladder” antibiotic used for clinical sepsis caused by enterobacteraciae is a carbapenem. There are one or two other options, but due to cost, safety and availability issues, for most institutions a carbapenem remains the broadest spectrum option utilised routinely by clinicians.

It would thus make a lot of (common) sense to protect carbapenems as much as possible in order to reduce selection pressure on bacteria, and prevent selection of MDROs such as carbapenem resistant enterobacteraciae (CRE)

I have thus put together a 10 point bundle (in no particular order) on reduction of carbapenem usage which I will call the CURB bundle (nothing to do with pneumonia severity…)

1) Restrict carbapenem usage to specific clinicians: Only allow prescribing of carbapenems where approval has been gained by an Infectious Diseases Physician or Clinical Microbiologist.

2) Restrict the range of carbapenems stocked by the Hospital Pharmacy:- Two would be sufficient.

3) Have a maximum prescription duration for carbapenems:- i.e. the carbapenem prescription would automatically expire after 3-5 days, and would need re-prescribed.

4) Regular audit of carbapenem use:- In terms of total hospital usage volume, and also audit of usage and indications in “high risk areas” such as ICU.

5) Feedback of audit results to all clinicians, both senior and junior, as well as nursing staff and hospital pharmacists.

6) Daily review of individual patients:- Does this patient still need a carbapenem today?

7) Removal of carbapenems from 1st line empirical antibiotic policies for the hospital. This is key to avoid widespread, high volume usage.

8) Removal of carbapenems from 1st line empirical therapy in neutropenic protocols:- Other suitable alternatives (or combinations) are almost always available…

9) Regular Education as to why widespread carbapenem usage is undesirable and where such usage can be safely reduced.

10) “Buy-in” of the above elements by clinical directors and hospital management:- Go right to the top for support.

None of the above are particularly new. However the idea behind a bundle is that the addition of separate elements with modest (and sometimes difficult to measure) effects should add up to a more major and measurable effect when done in composite.

The most important thing is not to take a defeatist attitude if you do have a problem with carbapenem resistant enterobacteraciae. I strongly believe that bundles like the above can be administered safely and can impact on both carbapenem usage and subsequently on CRE rates. I also believe that administration of such bundles is a more practical solution than waiting in “quiet desperation” for the next new even broader spectrum antibiotic to appear.

Michael