Tobramycin at subinhibitory concentration inhibits the RhlI/R quorum sensing system in a <it>Pseudomonas aeruginosa </it>environmental isolate

<p>Abstract</p> <p>Background</p> <p>Antibiotics are not only small molecules with therapeutic activity in killing or inhibiting microbial growth, but can also act as signaling molecules affecting gene expression in bacterial communities. A few studies have demonstrated the effect of tobramycin as a signal molecule on gene expression at the transcriptional level and its effect on bacterial physiology and virulence. These have shown that subinhibitory concentrations (SICs) of tobramycin induce biofilm formation and enhance the capabilities of <it>P. aeruginosa </it>to colonize specific environments.</p> <p>Methods</p> <p>Environmental <it>P. aeruginosa </it>strain PUPa3 was grown in the presence of different concentrations of tobramycin and it was determined at which highest concentration SIC, growth, total protein levels and translation efficiency were not affected. At SIC it was then established if phenotypes related to cell-cell signaling known as quorum sensing were altered.</p> <p>Results</p> <p>In this study it was determined whether tobramycin sensing/response at SICs was affecting the two independent AHL QS systems in an environmental <it>P. aeruginosa </it>strain. It is reasonable to assume that <it>P. aeruginosa </it>encounters tobramycin in nature since it is produced by niche mate <it>Streptomyces tenebrarius</it>. It was established that SICs of tobramycin inhibited the RhlI/R system by reducing levels of C4-HSL production. This effect was not due to a decrease of <it>rhlI </it>transcription and required tobramycin-ribosome interaction.</p> <p>Conclusions</p> <p>Tobramycin signaling in <it>P. aeruginosa </it>occurs and different strains can have a different response. Understanding the tobramycin response by an environmental <it>P. aeruginosa </it>will highlight possible inter-species signalling taking place in nature and can possible also have important implications in the mode of utilization for human use of this very important antibiotic.</p