However, it is their capability to accept
transferable b-lactamase genes that confer carbapenem
resistance at a level that will result in clinical failure that
causes most concern. In the mid 1990s, P. aeruginosa
strains isolated in Japan were found to harbour a transferable
class B metallo-b-lactamase called IMP-1 [19]. This
enzyme could increase the MIC to greater than 128mg/L
depending on the permeability characteristics of the
strain. This gene was thought originally to be confined
to southeast Asia but it and a myriad of similar genes
(blaIMP-2 – blaIMP-12) have now been isolated in P. aeruginosa
and other Gram-negative bacteria from around the
world. A similar class of b-lactamases (VIM 1–4) have
been found in Asia and Europe, almost exclusively in
P. aeruginosa [20]. The extent and diversity of these
enzymes suggests that they will be very difficult to
overcome