Enterobacteriacae (gram negative rods) include E. coli, Salmonella and Klebsiella sp. which are important human pathogens. Resistance of the Enterobacteriacae to antibiotics, particularly beta-lactams, is a growing clinical problem. Over use of antibiotics has changed the natural evolution of bacteria creating mobile genes that rapidly spread resistance through populations. Even in countries with controlled antibiotic use have seen significant increases in resistant strains. In Canada and Australia the rate of extended spectrum beta-lactam resistance in E. coli has doubled in the last five years.Antibiotic resistant strains of bacteria can spread around the world in a number of ways that have nothing to do with an individuals antibiotic use. They can be spread by travellers and through animals in the food chain. This is another reason why reducing the overall amount of antibiotics in the environment is important.
The exchange of genetic material is an effective and efficient way of bacteria sharing genes which offer a survival advantage, such as those encoding resistance. In this way antibiotic resistance can also spread between bacteria that are not pathogenic to humans to bacteria which are. There is currently to way to predict the way these genes will spread, or where they will come from next.
So what does this seemingly unrelenting spread of resistance mean for our patients?
It means their infections are becoming harder to treat. The authors of a recent review of Enterobacteriacae resistance offer several thoughts on treating patients who have been infected with a resistant organism:
- Extended infusion regimens may be effective if the MIC is only slightly above the resitance breakpoint
- Use newer antibiotics, such as tigecycline (although this has it own problems)
- Use older antibiotics, such as colistin (although these were usually abandoned due to toxicity)
The Therapeutic Guidelines: Antibiotic recommends meropenem for beta-lactam resistant organisms and seeking expert advice. If a carbapenem resistant organism is detected treatment options are extremely limited- seeking expert advice is the only option listed.
The review, published in the BMJ, covers in detail the development of resistance in Enterobacteriacae, methods of measuring resistance and clinical implications of this resistance.