Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2008
Publication Date: 5/1/2008
Citation: Dowd, S.E., Killinger-Mann, K.M., Brashears, M.M., Fralick, J.A. 2008. Evaluation of gene expression in a single antibiotic exposure derived mutant isolate of Salmonella enterica typhimurium 14028 possessing resistance to multiple antibiotics. Foodborne Pathogens and Disease. 5(2):205-221. Interpretive Summary: Antibiotics are important tools used to control infections.Unfortunately, microbes can become resistant to antibiotics, which limits the drugs' usefulness for clinical and veterinary use. ARS scientists collaborating with TTU, TTUHSC, and WSU derived a multi-drug resistant mutant of Salmonella and utilized modern molecular genetics techniques to study how such resistance develops. Results indicate a variety of physiological changes in the bacteria which promote elimination of the antibiotics from the pathogen's cells and other mechanisms that prevent antibiotics from entering the cell. These results will allow scientists to better understand the molecular, genetic, and physiological changes that contribute to antibiotic resistance in these pathogens. Such understanding will improve our ability to prevent the development of antibiotic resistance and our ability to design better treatments for these pathogens.
Technical Abstract: Antibiotics are important tools used to control infections.Unfortunately, microbes can become resistant to antibiotics, which limits the drugs' usefulness for clinical and veterinary use. It is necessary to improve our understanding of mechanisms that contribute to or enhance antibiotic resistance. Using nalidixic acid exposure as a sole selective agent, a mutant strain of Salmonella typhimurium 14028 was derived that had acquired resistance to chloramphenicol, sulfisoxazole, cefoxitin, tetracycline, and nalidixic acid. We employed gene array analyses to further characterize this mutant. Our results indicate a significant difference (p < 0.02; FDR < 5%) in the expression of 338 genes (fold regulation > 2.5) between the mutant and the parent strain growing exponentially under the same conditions at 37 deg C. The mutant 2a showed comparative induction of SPI2 transcripts and repression of SPI1 genes. The primary differences in expression were related to efflux pumps (increased), porins (decreased), type III secretion systems (increased), LPS synthesis (decreased), motility-related genes (decreased), and PhoP/PhoQ and peptidoglycan synthesis (increased). Based on our results, it appears that the multi-antibiotic resistant mutant developed altered regulation of gene expression to decrease the influx and increase the efflux of deleterious environmental agents (antibiotics) into and out of the cell, respectively. The mechanism(s) by which this was accomplished or the reason for alterations in gene expression of other genetic systems (curli, flagella, PhoP/PhoQ, and peptidoglycan) is not immediately apparent. The evaluation of transcriptomes within multiple-antibiotic-resistant mutants hopefully will enable us to better understand those generalized mechanisms by which bacteria become resistant to multiple antibiotics.