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Title:   Author  item
                                            Brunelle, Brianitem
                                            Bearson, Shawnitem
                                            Bearson, Bradley

                                                         - *Brad*
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 2/21/2014
                                    Publication  Date: 5/20/2014
                                    Citation: Brunelle, B.W., Bearson, S.M., Bearson, B.L. 2014. Antibiotics induce the expression of attachment genes in specific isolates of Salmonella enterica serovar Typhimurium [abstract]. In: Proceedings of 114th General Meeting of the American Society for Microbiology, Boston, Massachusetts, May 17-20, 2014. p. 204.Interpretive Summary:
                                Technical Abstract: More than 27 percent of Salmonella enterica serovar Typhimurium isolates from humans in the United States are resistant to three or more antibiotics.  This presents an important food safety concern as multidrug-resistant (MDR) Salmonella is associated with increased morbidity in humans.  It has been reported that antibiotics can affect cellular processes in bacteria, and our goal was to establish differences in transcriptional regulation in MDR S. Typhimurium isolates after exposure to tetracycline and chloramphenicol.  We have previously shown that in vitro exposure to tetracycline and chloramphenicol can induce a fully invasive phenotype in several MDR S. Typhimurium DT193 isolates during early-log growth; this is important as optimal Salmonella invasion typically occurs during late-log to stationary phase, with limited invasive capabilities during early-log.  We used RNA-seq to ascertain global gene expression changes in these DT193 isolates after 30 minutes of exposure to each antibiotic compared to the same isolates not treated with an antibiotic.  The transcriptomic analyses identified that attachment, SPI-1, SPI-2, and SPI-3 genes are up-regulated, while genes associated with motility are down-regulated.  Within the group of genes associated with attachment, up to ten fimbrial operons (bcf, csg, fim, lpf, saf, stb, stc, std, stf, and sth) were up-regulated.  This is unusual as only lpf and csg operons are considered to be inducible in vitro, and normal induction does not occur until much later during the growth phase.  The other fimbrial genes are thought to only be expressed in vivo, with previous studies indicating that the bcf, lpf, stb, stc, std, and sth operons are associated with persistence in mice.  Visualization of the isolates by electron microscopy indicated that isolates treated with either antibiotic had fewer flagella and increased agglutination, which is consistent with the RNA-seq data.  Our study demonstrates that tetracycline and chloramphenicol promote the expression of fimbrial genes that are linked to increased colonization and persistence in the host; such an effect may play a role in increasing the duration and intensity of MDR Salmonella colonization and infection.


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