There is a new report in PNAS by investigators in Australia and the UK that looked at gene expression in A. baumannii after chlorhexidine exposure. The most highly up-regulated genes were those encoding the RND efflux system AdeAB. Importantly, the investigators also identified a gene encoding a previously uncharacterized membrane protein, AceI, which they determined to be an active CHG efflux protein capable of transporting CHG out of the cell. This novel AceI was said to be a member of the PCE family of efflux systems.
And to give you a sense of the ubiquity and potential importance of these systems in Gram-negative bacteria, I offer this quote from the authors: “The primary features of the A. baumannii chlorhexidine resistance response, i.e., up-regulation of genes encoding RND and PCE family efflux systems, are conserved in other γ-proteobacteria, as well as β-proteobacteria. Given the phylogenetic distance of these organisms, this similarity of regulatory responses to a compound that has only been synthesized since the early 20th century is intriguing. RND efflux systems are well recognized for their broad protective functions in Gram-negative bacteria and it is not unusual for these systems to constitute part of a general stress response and to mediate resistance to foreign compounds, particularly amphipathic antimicrobials such as chlorhexidine. However, the involvement of the PCE family proteins in seemingly specific resistance to chlorhexidine is unexpected. It is likely that the physiological function(s) of this transporter family were originally unrelated to chlorhexidine resistance and that these proteins provide a fortuitous intrinsic resistance capacity.”
h/t Ayush Kumar and Dan Ricciuto
Eli N. Perencevich, MD, ACP Member, is an infectious disease physician and epidemiologist in Iowa City, Iowa, who studies methods to halt the spread of resistant bacteria in our hospitals (including novel ways to get everyone to wash their hands). This post originally appeared at the blog Controversies in Hospital Infection Prevention.