Because what we really need are more ways to have carbapenem resistant enterobacteriaceae (‘CRE’), which are bacteria resistant to all penicillin derivatives–and almost always resistant to just about every other antibiotic. While the two ‘famous’ types of carbapenem resistance genes, KPC and NDM-1, are usually discussed, there are other classes of genes, one of which goes by the name VIM (short for Verona integron-encoded metallo-beta-lactamase which just rolls right off the tongue, doesn’t it?).
These genes, like KPC and NDM-1, are carried on plasmids (mobile mini-chromosomes that can move from bacterium to bacterium), but these plasmids are not the same plasmids as those that carry KPC and NDM. Increasingly, we are seeing strains that have both KPC and VIM plasmids. Not only are these strains resistant, but transfer of either plasmid will confer carbapenem resistance on the recipient.
Worse, at least one allele, VIM-24, doesn’t confer resistance in all strains. In this particular case, in the clinical Klebsiella pneumoniae isolate, it doesn’t confer resistance, but when transferred in the lab to a strain of E. coli it does. In other words, there might be more VIM-24 lurking out there–which we won’t always detect–that will confer resistance when acquired by the right (or perhaps wrong is the better word) strain.
This is not helping.
Rojas LJ, Mojica MF, Blanco VM, Correa A, Montealegre MC, De La Cadena E, Maya JJ, Camargo RD, Quinn JP, Villegas MV. 2013. Emergence of Klebsiella pneumoniae Coharboring KPC and VIM Carbapenemases in Colombia. Antimicrob Agents Chemother. 2013 Feb;57(2):1101-2. doi: 10.1128/AAC.01666-12.
Steinmann J, Kaase M, Gatermann S, Popp W, Steinmann E, Damman M, Paul A, Saner F, Buer J, Rath PM. Outbreak due to a Klebsiella pneumoniae strain harbouring KPC-2 and VIM-1 in a German university hospital, July 2010 to January 2011 . Euro Surveill. 2011;16(33):pii=19944. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19944