title: Contribution of stress responses to antibiotic tolerance in Pseudomonas aeruginosa biofilms.
abstract: Enhanced tolerance of biofilm-associated bacteria to antibiotic treatments is likely due to a combination of factors, including changes in cell physiology as bacteria adapt to biofilm growth and the inherent physiological heterogeneity of biofilm bacteria. In this study, a transcriptomics approach was used to identify genes differentially expressed during biofilm growth of Pseudomonas aeruginosa. These genes were tested for statistically significant overlap, with independently compiled gene lists corresponding to stress responses and other putative antibiotic-protective mechanisms. Among the gene groups tested were those associated with biofilm response to tobramycin or ciprofloxacin, drug efflux pumps, acyl homoserine lactone quorum sensing, osmotic shock, heat shock, hypoxia stress, and stationary-phase growth. Regulons associated with Anr-mediated hypoxia stress, RpoS-regulated stationary-phase growth, and osmotic stress were significantly enriched in the set of genes induced in the biofilm. Mutant strains deficient in rpoS, relA and spoT, or anr were cultured in biofilms and challenged with ciprofloxacin and tobramycin. When challenged with ciprofloxacin, the mutant strain biofilms had 2.4- to 2.9-log reductions in viable cells compared to a 0.9-log reduction of the wild-type strain. Interestingly, none of the mutants exhibited a statistically significant alteration in tobramycin susceptibility compared to that with the wild-type biofilm. These results are consistent with a model in which multiple genes controlled by overlapping starvation or stress responses contribute to the protection of a P. aeruginosa biofilm from ciprofloxacin. A distinct and as yet undiscovered mechanism protects the biofilm bacteria from tobramycin.
authors: Department of Chemical and Biological Engineering and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA phil_s@biofilm.montana.edu.
authors: Philip S
authors: PS
authors: Stewart
authors: Department of Microbiology and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA.
authors: Michael J
authors: MJ
authors: Franklin
authors: Department of Microbiology and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA.
authors: Kerry S
authors: KS
authors: Williamson
authors: Department of Chemical and Biological Engineering and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA.
authors: James P
authors: JP
authors: Folsom
authors: Department of Chemical and Biological Engineering and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA.
authors: Laura
authors: L
authors: Boegli
authors: Department of Chemical and Biological Engineering and Center for Biofilm Engineering, Montana State University, Bozeman, Montana, USA.
authors: Garth A
authors: GA
authors: James
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D018441:Biofilms / Q000187:drug effects*; D001692:Biological Transport / Q000235:genetics; D015687:Cell Hypoxia; D002939:Ciprofloxacin / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D008025:Ligases / Q000235:genetics; D009997:Osmotic Pressure; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011755:Pyrophosphatases / Q000235:genetics; D053038:Quorum Sensing / Q000235:genetics / Q000502:physiology; D013014:SOS Response, Genetics / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics; D013312:Stress, Physiological / Q000235:genetics*; D014031:Tobramycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D002939:Ciprofloxacin; C027627:guanosine-3',5'-bis(diphosphate) 3'-pyrophosphatase; D011755:Pyrophosphatases; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases; D014031:Tobramycin