A-040. Involvement of a Novel Efflux System in Biofilm-Specific Resistance to Antibiotics

L. Zhang, T-F. Mah;
Univ. of Ottawa, Ottawa, ON, CANADA.

Bacteria growing in biofilms are more resistant to antibiotics when compared to their planktonic counterparts. How this transition occurs is unclear, but it is likely there are multiple mechanisms of resistance that act together in order to provide an increased overall level of resistance to the biofilm. Through the success of a genetic screen, we have identified a novel efflux pump in Pseudomonas aeruginosa that is important for biofilm-specific resistance to a subset of antibiotics. Using planktonic- and biofilm-specific minimal bactericidal concentration assays, we have shown that a complete deletion of the genes encoding this pump, PA1874-1877, results in an increase in biofilm-specific sensitivity to tobramycin, gentamycin and ciprofloxacin. Semi-quantitative RT-PCR experiments revealed that this efflux pump is more highly expressed in biofilm cells than planktonic cells, providing an explanation for why these genes are important for biofilm but not planktonic resistance to antibiotics. We have previously shown that ndvB is important for biofilm-specific resistance. Combining the ndvB mutation with the PA1874-1877 deletion results in a mutant strain that is more sensitive to antibiotics than either single mutant strain, suggesting that these two loci represent separate mechanisms for biofilm-specific resistance.