Tag Archives: malditof

“Maldi-tof: Taking the fun out of External QC”

Future of Microbiology,

With regards to bacteriology, Maldi-tof has somewhat taken the fun out of External Quality Control programmes, particularly with regards to organism identification (you might say external QC was never much fun in the first place).

No longer do we need to sweat for days over some obscure, biochemically inert organism, looking up the textbooks as we go along for inspiration, and consulting anyone and everyone.

In my short experience with Maldi-tof it is generally very accurate, apart from the odd caveat which are generally well known anyway (eg Shigella & E. coli; Strep. pneumoniae & S. mitis)

So the external QC results are now as a consequence often very good, and we can give ourselves a pat on the back, but do we need to move the bar yet higher?

Maldi-tof may trigger a move away from traditional external QC programmes and direct focus on interpretation of mixed cultures, ascertaining pathogenicity of bacteria isolated from different sites, appropriate result comments, and pre and post analytical errors. This would be good for several reasons, not only because it more accurately reflects our day to day work, but such QC is also more interesting and more challenging, possibly triggering more healthy debate also.

I am not saying that organism identification should be ignored completely by external QC programmes, but bacteriology has always been much more than that, and QC programmes should reflect this….

Michael

Apologies for the technical problems with the website yesterday. I contacted the web hosting company last night and they did what all the best IT people do…., turn the system off and switch it back on again..!

“Re-writing the textbooks on Coagulase Negative Staphylococci”

Future of Microbiology,

With the introduction of MALDI-TOF we are inevitably going to see the textbooks re-written on Coagulase Negative Staphylococci (CoNS).

MALDITOF

Compared with the traditional biochemical means of identifying CoNS (cumbersome and expensive), with MALDI-TOF we can now identify CoNS accurately and at virtually no cost. Therefore we are going to start learning a lot more about CoNS, their local epidemiology, and the pathogenic potential and preferential colonisation/infection sites of different CoNS strains.

As this knowledge increases, more and more clinicians will want to know exactly what type of CoNS is growing, not just that it is a CoNS. I think that laboratories will increasingly be expected to report the exact staphylococcal species type rather than lumping them all into the one CoNS group….

Our experience so far using MALDI-TOF to identify CoNS in our laboratory has shown a predominance of S. epidermidis, S. warneri, S. haemolyticus, S. capitis and S. saprophyticus strains. It is too early just yet however to draw any more detailed conclusions on the individual CoNS strains. This will come in due course.

Expect to see a few journal articles on this topic in the next few years…. I will keep you updated on the expected MALDI-TOF inspired progress in this area.

Michael

Click here for a quick tutorial on the basics of MALDI-TOF.

 

“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