Tag Archives: mrsa

“There is always a flipside….”

The Science of Microbiology, ,

It is fascinating to compare differences in antibiotic prescribing practices between New Zealand and the UK.

In the UK, due to high MRSA and C. difficile rates there has been a national drive to reduce/eradicate routine prescribing of cephalosporins and beta-lactam/beta lactamase inhibitor combinations. This (along with increased infection control measures) has had dramatic effects on MRSA and C. difficile rates. When I left for New Zealand in 2006, MRSA rates in the UK were up at 35% of all Staph aureus isolates. Now on my return it is down closer to 10%, much the same as in New Zealand.

However there are potential downsides to such a change. As a consequence there is much more prescribing of gentamicin for Gram negative cover. It is generally given to more patients and in longer duration. This potentially increases the risk of both ototoxicity and nephrotoxity. There is also increased prescribing of vancomycin and possibly as a consequence, Vancomycin Resistant Enterococci are more of an issue in the UK than in NZ, where they are very rare.

In terms of efficacy, beta-lactams are often thought of as the most efficacious antibiotics, so there is also a potential concern that avoidance of these antibiotics (with the exception of amoxycillin) may lead to increased numbers of clinical failures. To prove this objectively however would be incredibly difficult, if not impossible.

It is interesting that some of my antibiotic recommendations/advice given in New Zealand would be seen as ridiculous here in the UK, and vice versa…. Not wishing to look like the fool that I am,  I have learnt to adapt very quickly to the prescribing culture here!

Nevertheless it is difficult to argue with the very impressive reductions in MRSA and C.diff rates here in the UK . However there is always a flipside….

Michael

 

“MRSA, MSSA and resistance v virulence”

Antimicrobial Resistance, The Science of Microbiology, ,

There are three sound reasons why mortality in sepsisStaph aureus culture due to Methicillin Resistant Staphylococcus aureus (MRSA) is higher than that of Methicillin Susceptible Staphylococcus aureus (MSSA).

 

  • If the patient is put on initial treatment that just covers MSSA and not MRSA, then effective therapy may be delayed.
  • The antibiotic most commonly used for treating sepsis due to MSSA (flucloxacillin, cloxacillin) is a more effective antibiotic than that usually used for MRSA sepsis (vancomycin)
  • The cohort of patients with MRSA sepsis tends to be a “sicker” cohort (ie more co-morbidities, more prior antibiotics, more hospital admissions etc) than that of patients with sepsis due to MSSA. (This is particularly true for “hospital type” MRSA strains.)

Some people/experts suggest a fourth reason, that MRSA may be a more virulent bacterium per se than MSSA. Some research trials have actually claimed this. However such trials are fraught with difficulty. It is hard enough to attribute mortality to a particular micro-organism. Throw in the confounding variables as described above and you are on a hiding to nothing.

However there are theoretical reasons why MRSA should not be more virulent than MSSA. Generally a bacterium utilises energy in order to become resistant. Sometimes, but not always, this energy is the energy used for making virulence factors within the bacterium.

It doesn’t make any logical or evolutionary sense that MRSA should be both more resistant and more virulent per se than MSSA.

On the contrary it may well be that the converse is true, that MRSA is a slightly less virulent bacterium than MSSA.

Trying to convince the “experts” of this is another matter…..

Michael

The link between bacterial resistance and virulence is very interesting. Unfortunately the more you read about it, the more complex it gets. More on this topic in later articles….

Antimicrobial Resistance in New Zealand

Antimicrobial Resistance, , ,

These are approximate antimicrobial resistance rates in NZ currently:

9% of all Staph aureus isolates are resistant to methicillin (MRSA).

1% of all E.coli isolates are Extended Spectrum Beta Lactamase producers (ESBLs).

10% of all Klebsiella pneumoniae isolates are ESBLs.

<1% of all enterococci are vancomycin resistant (VRE).

There are just a handful of metallobetalactamases, mostly in people who have travelled abroad.

 

By international standards I think these are very low rates. How do they compare with the country you live in?

It would be nice to think that this was due to the great antimicrobial stewardship, fantastic infection control and well regulated antimicrobial licensing that we have in NZ! Off course these all play a part, but in actual fact the more likely reasons are due to NZ’s geographical isolation and sparse population, which are inherent advantages.

Let’s hope that the rates stay this low…

Michael