Tag Archives: carbapenems

“Too much knowledge…”

The Science of Microbiology, ,

shutterstock_knowledge

A little bit of knowledge can be a bad thing. So can too much…

The acronym  ESCHAPPM ( or something similar) will be familiar to most microbiologists. (a similar acronym SPICE, is sometimes used instead)

  • Enterobacter spp.
  • Serratia spp.
  • Citrobacter freundii
  • Hafnia spp.
  • Aeromonas spp.
  • Proteus spp.
  • Providencia spp.
  • Morganella morganii

Because we are clever microbiologists, we know this group of organisms may have inducible beta-lactamase activity, and we advise the clinicians of this, often provoking a reflex switch in anti-microbial therapy to carbapenems. Not only clinicians, but there are plenty of ID physicians who make this automatic transfer to carbapenems the moment the word ESCHAPPM is mentioned, my hospital included.

The thing is however, do all patients with infections by an ESCHAPPM organism require a carbapenem?

Almost certainly not…

If we use a carbapenem for every infection due to one of these organisms, then this amounts to a significant amount of carbapenems. This is therefore an important an important antimicrobial stewardship issue. We are supposed to be trying to decrease the use of broad spectrum antibiotics, not increase them.

But we have read the textbooks, and we are clever…

And yet, if we look at the literature, there is very little evidence to support the theoretical dangers of using a beta-lactam in such patients. In fact, there are several small studies out there that support the non-inferiority of beta-lactams in such patients, particularly in non-life threatening illnesses.

Not to mention there are other options out there, fluoroquinolones, sulphonamides, etc.

We are simply scared.

Here is what I generally do (rightly or wrongly):

  • In a patient with bacteraemia due to an ESCHAPPM organism, as long as they are clinically improving I am happy to continue therapy based on the phenotypic susceptibility results.
  • In patients with UTIs due to ESCHAPPM organisms, even if in hospital, I feel no need  whatsoever to move to carbapenems.
  • I reserve carbapenem use in “ESCHAPPM” patients to bacteraemic patients who are getting worse, and also for patients with chronic infections, e.g. prosthetic joint infection, on the rationale that the longer the treatment, the more chance you have of getting clinically relevant inducible beta-lactamase activity.

We need to take a more pragmatic approach to ESCHAPPM organisms and their treatment. We also need larger scale trials so we can be more confident in our decisions and adopt such approaches into guidelines.

and we need to be brave…

Michael

“Carbapenemases: As old as the Hills..”

History of Microbiology, The Science of Microbiology, , ,

There has been a lot in the press recently about carbapenem resistant enterobacteraciae (CRE).

As people with a professional interest in infection, it is important we know in detail the origins of carbapenems and carbapenemases. Such knowledge and understanding also focuses the mind when trying to control them.

"Meropenem molecule"
“Meropenem molecule”

Carbapenems are derived from Thienamycin, a naturally occuring substance found in Streptomyces cattleya, which is a bacteria found commonly in soil in the environment. Other bacteria residing close to these carbapenem like substances in the environment thus have to protect themselves to avoid being destroyed. Thus carbapenemases evolved in other environmental bacteria such as Bacillus cereus, Bacillus anthracis and Shewanella, amongst others.

What we have done is take these naturally occuring compounds, purified them (with only very minor modifications), concentrated them and started administering them to humans in the form of carbapenem antibiotics, thus ramping up the selection pressure on the human bacterial flora.

It is thus not surprising that human enterobacteraciae, faced with this selection pressure have decided that they want defences against carbapenems, and have “acquired” the resistance genes from the environmental bacteria, most likely by transfer on mobile genetic elements.

Many people still perceive carbapenemases as being a relatively new phenomenen. We know that they are not new however. Both carbapenems and carbapenemases have probably been around for millions of years. We have just moved the battle between carbapenems and carbapenemases from the “hills” into the human flora, where it really matters….

Michael

Off camping this weekend!, I will write a short article next week sometime on “protecting the carbapenems”.