Physiological functions of multidrug efflux pumps in the nosocomial pathogen Acinetobacter baumannii

The success of A. baumannii as a pathogen may be attributed to its broad resistance capabilities, and its ability to persist in the clinical setting and infect new hosts. Multidrug efflux pumps may play important roles in each of these factors. The role of multidrug efflux pumps in conferring resistance to antibiotics is of clinical relevance and has been well studied. However it is becoming increasingly apparent that these efflux pumps may have physiological roles such as colonisation of the bacterium in hosts; maintaining cellular homeostasis by mediating extrusion of endogenous polyamines and playing a role in cell-to-cell signalling which ultimately controls biofilm formation.To determine if multidrug efflux pumps have physiological roles in biofilm formation and resistance to host produced factors a mutant library from strain AB5075-UW was screened. Disruption of several chromosomally encoded efflux pump genes resulted in either significantly higher or lower biofilm formation. Efflux pumps which showed significant differences in biofilm were screened for polyamine transport. It was found that MATE efflux pump mutant ABUW_0109-152::T26, which displayed a loss of biofilm formation, was sensitive to the polyamine spermine. Therefore, spermine may be a native substrate of this efflux pump and play a role in biofilm regulation.