Modulation Of Genes By Subinhibitory Concentrations Of Antibiotics In Pseudomonas Aeruginosa

Antibiotics have been commonly used as therapeutics to treat bacterial infections in humans and animals, and thus been perceived as bacterial killing or inhibiting agents in nature. However, recent studies have shown subinhibitory antibiotics play important roles in regulating bacterial genes including virulence factor genes. In this study, the expression of 13 secreted virulence related gene clusters of Pseudomonas aeruginosa, an important opportunistic pathogen, was examined in the presence of subinhibitory concentrations of four antibiotics using luxCDABE-based promoter-reporter fusion constructs. The results indicate that five of the 13 gene clusters, rhlAB, phzA2, lasB, exoY and exoS, were activated by all four sub-MIC antibiotics Vancomycin, tetracycline, ampicilin and azythromycin; phzA1 was also activated by them except ampicillin, in contrast to the previous observations that antibiotics at subinhibitory concentrations generally reduce bacterial virulence. Analysis of rhlAB showed 1/4-MIC Vancomycin resulted in 10-fold increase of its transcription. Rhaminolipid production that is carried out by rhaminosyltransferase encoded by rhlAB was also increased significantly, and so was pyocyanin production as well as P. aeruginosa swarming and swimming motility. Similar results were observed with subinhibitory tetracycline, azithromycin and ampicillin. These results indicate that the antibiotics at low concentrations could up-regulate virulence factors and therefore influence bacterial pathogenesis, supporting the notion that antibiotics at low concentrations can act as intermicrobial signaling molecules in specific environments.Vancomycin, tetracycline, ampicilin, polymixin, kanamycin, ciprofloxacin, rifampicin, chloramphenicol and erythromycin were used to screen P. aeruginosa random promoter library for potential antibiotics responsive genes. The genes that regulated by sub-MIC antibiotics were identified by PCR amplification and sequence blast. The regulated genes were used to test antibiotics response on solid media and a mini-compound-library that contains 32 chemicals was checked.PA5283, which encodes a potential transcriptional regulator, was regulated by some antibiotics at subinhibitory concentrations. Through gene knockout, PA5283 was found to down-regulate the expression of some virulence factors as well as QS system, suggesting it is possibly a mumber in the QS pathways.