Regulation Of RND Pumps Genes By Sub-inhibitory Concentrations Of Antibiotics And Zinc In Pseudomonas Aeruginosa

Pseudomonas aeruginosa is a major opportunistic pathogen in humans. The infections caused by P. aeruginosa is a serious problem in hospitals. It has been reported that 10-30% of all nosocomial infections are resulted from P. aeruginosa. Although it is not a very virulent bacterium in general it has high intrinsic multidrug resistance against many clinically useful antibiotics. Drug resistance posts a serious threat to patients especially immunocompromised patients such as cancer and AIDS patients. It is critical to study drug resistance mechanisms and pathogenesis of P. aeruginosa in order to understand and eventually control its infections.P. aeruginosa intrinsic resistance results mainly form the low permeability of the outer membrane and drug efflux by varies trans-membrane pumps, especially the Resistance Nodulation Division (RND) efflux pumps. Bioinformatics analysis indicates that there are twelve known and putative RND efflux systems in the P. aeruginosa genome which are the subjects of this study. All these RND efflux pump systems are investigated at the transcriptional level. The promoters of the RND pump genes are cloned respectively into a low-copy plasmid containing promoterless luxCDABE reporter.This reporter enables monitoring gene expression by light production, and promoter activity is measured as amount of luminescence. The regulation of these RND pumps by various compounds including sub-inhibitory concentrations of antibiotics, organic solvents and heavy metal irons.The results indicate: gentamycin induced the expression of RND J and I; J was strongly induced at the present of tetracycline, but not oxytetracycline; 11 of the 12 RND systems were induced by ampicillin. No effect was asserted on the RND pump genes by organic solvents such as ethyl ether. The RND pump encoded by the gene cluster, PA4206 PA4207 and PA4208 was activated not only by antibiotics but also by metal ion zinc. The RND pump encoded by the gene cluster, czcCBA, was active only at the presence of metal ion such as zinc and cobalt, but it is also activated by antibiotics in this condition. It seems apparent that these pumps coordinately export different kinds of antibiotics and there is a synergistic effect between antibiotic efflux and metal ion export in some cases.