Monthly Archives: January 2013

“Antimicrobial Susceptibility Testing on MALDI-TOF: The Holy Grail”

We already know that Maldi-tof is a “no brainer” for most routine diagnostic microbiology labs. (Click here for a nice article on the realities of putting a Malditof instrument into a diagnostic laboratory)MALDITOF

However if we could also perform anti-microbial susceptibility testing on Maldi-tof in addition to microbe identification, then it would take it to another level altogether…

There has been a lot of recent work in this area. A nice paper  in Clinical Microbiology Reviews summarises this work. (Unfortunately it is not free to access. Here is the abstract. I hope your institution can obtain it for you.)

I will summarise where the research is at:

  1. Detection of carbapenemases: This is progressing well. the technique involves incubating the bacteria and the carbapenem, and then analysing the products with Malditof. If the bacteria contains a carbapenemase that can lyse the carbapenem then the specific spectra for the degradation products of the carbapenem can be detected. Similar methods are also being developed to look for other beta-lactamases as well as aminoglycoside modifying enzymes.
  2. Detection of MRSA (Methicillin Resistant Staphylococcus Aureus). Specific spectral peaks for MRSA are identifiable, but are quite subtle and difficult to reproduce in a consistent manner at present. More work needed.
  3. Detection of VRE (Vancomycin Resistant Enterococci). Detection of the Van A and Van B “genotypes” now well validated in a research setting. Should not be too long before this becomes routine in diagnostic laboratories.
  4. Detection of ESBLs (Extended Spectrum Beta Lactamases): Difficult… A newer technique named mini-sequencing may have potential. This involves using the fact that specific mutations produce specific differences in molecular mass. However it require DNA amplification and still quite labour and time intensive. This technique could also be used to detect mutations responsible for resistance in Neisseria gonorrhoeae, Streptococcus pneumoniae etc.

It looks like VRE detection and carbapenemase detection are the most likely to become routine Maldi-tof techniques in diagnostic laboratories over the next few years. MRSA detection I suspect is not too far away either. The rest is going to take some time and the paper concludes that proteomic approaches in the detection of resistant organisms is only ever likely to complement, not replace, standard susceptibility testing.


p.s If you are a student studying for microbiology exams in the next year or two, I would advise that you ensure you know all about Maldi-tof! In addition, knowledge of future potential applications is likely to separate out the distinction candidates from the passes….

“Antimicrobial Stewardship in the Hospital Setting: The Dilemma….”

The Dilemma (or is it dilemna!)

The individual patient v the population: Potentially every patient that walks in the door of the hospital with clinical sepsis could be given the broadest spectrum antimicrobial available on the formulary. This might give the individual the best chance of survival from their sepsis but such management will have the potential to select out Multi Drug Resistant Organisms (MDROs) and cause/store up problems on a population basis.

Antibiotic Stewardship policies are often based on balancing treating the individual patient against minimising MDRO selection in the population.

One could argue that in the making of such policies, general physicians would be most focused on treating the individual patient, clinical microbiologists would be most focused on minimising MDROs in the population, and ID physicians are somewhere in between. A generalisation and an assumption of course but I suspect there may be an element of truth in it. I guess this is why we have stewardship committees with representatives from all these groups.

Communities/cultures may exist where the importance of treating the individual is prioritised; i.e if there is a low threshold for legal action should the patient suffer as a consequence of not receiving the “correct” antimicrobial. This in turn leads to broader spectrum antimicrobial policies and in turn MDRO selection.

And of course there can be micro-cohorts of patients within the hospital setting such as ICU patients. In such cohorts the severity of sickness tips the balance towards treating the patient with the best possible antimicrobial and MDRO minimisation takes a relative back seat. This is why ICUs often become micro-environments within the hospitals for MDROs.

Antimicrobial Stewardship is a (very) complex area and it’s implementation often becomes very political, often because of The Dilemma. The one good thing from my point of view is that it often involves lots of concepts rather than facts. There is a lot out there on the Internet on Antimicrobial Stewardship, most of which is fairly dull reading. To read some more on the varying elements of antimicrobial stewardship click here for a readable and relatively concise article.


See also Anti-microbial Stewardship in the Hospital Setting: “The Vicious Circles of Resistance”

“Textbooks: A Laboratory Hazard?”

Every laboratory I have been to has at least one or two shelves of textbooks. I am talking here about the traditional paper textbook.120px-Paperback_book_black_gal_svg

On looking more closely at the textbook collection of each laboratory, there might be a couple that are up to date, then the rest will undoubtedly be of varying ages with a few of antique value.

So how old does a textbook have to be before it loses it’s usefulness? Well, like people they all age at different rates. It depends to some extent on what has changed with regards to the topic matter. You might find a book on syphilis is still useful 10-15 years after publication, whereas a book on Hepatitis C treatment would be almost useless only 5 years from the date of issue due to the rapid changes in this area..

In general most of us still like paper textbooks because it is what we were brought up with. It is how we learnt. However I am concerned that by referring to out of date textbooks in the laboratory, we are not doing ourselves or the patients any favours.

I still have a few paper textbooks on my shelves (It makes vistors believe I am a microbiologist!). However I try and force myself not to use them as they are all years out of date.

I would encourage laboratories to move towards online texts (even then it is still important to check the publication date) and to clear those shelves, maybe apart from the antique textbooks which can be put behind lock and key for the safety of both the book and the user…