The risk of interspecies transmission of carbapenemase genes is a real concern. We can barely get our heads around many different types of carbapenemase in a whole host of Gram-negative bacteria (compare the relative simplicity of methicillin resistance in S. aureus: a single gene, in a single species). Throw in interspecies horizontal transmission of carbapenemases and things get really tricky! Do we implement different control strategies to try to interrupt the transmission of carbapenemases (in contrast to the organisms themselves)? Could you have a multispecies outbreak of a carbapenemase on your hands and not even realise it?