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Title:   Author  item
                                            Brunelle, Brianitem
                                            Bearson, Bradley

                                                         - *Brad*item
                                            Bearson, Shawn
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/18/2015
                                    Publication  Date: 5/1/2015
                                    Citation: Brunelle, B.W., Bearson, B.L., Bearson, S.M. 2015. Differences in the motility phenotype of multidrug-resistant Salmonella enterica serovar Typhimurium exposed to various antibiotics. American Society of Microbiology Conference on Antimicrobial Resistance in Zoonotic Bacteria and Foodborne Pathogens, May 8-11, 2015, Washington, DC. p. 26.Interpretive Summary:
                                Technical Abstract: Salmonella enterica serovar Typhimurium (S. Typhimurium) is one of the most prevalent foodborne-associated bacteria in humans and livestock, and over 35 per cent of these isolates are resistant to three or more antibiotics.  This is a concern as multidrug-resistant (MDR) Salmonella has been associated with increased clinical disease in patients compared to antibiotic-sensitive isolates.  Motility is often considered a virulence factor in pathogenic bacteria; therefore, our goal was to test the effect several antibiotics had on swimming and swarming motility of MDR Salmonella.  

Six MDR S. Typhimurium isolates of bovine origin that encoded antibiotic-specific resistance genes to chloramphenicol, kanamycin, streptomycin, and tetracycline were selected for study.  We performed phenotypic assays for swimming and swarming in response to each antibiotic at several sub-inhibitory concentrations.  The antibiotic concentrations were chosen based on having no effect on bacterial growth in liquid or on solid media.  Swimming is described as the movement of individual bacteria through a surface, and we tested the swimming phenotype by inoculating the appropriate Salmonella isolate in the center of 0.3 per cent agar Luria Broth (LB) plates with and without antibiotics.  Swarming is the movement of a group of bacteria across a surface, and we assessed the swarming phenotype by inoculating the appropriate culture in the center of 0.6 per cent agar LB plates with and without antibiotics.  The diameter of the swim and swarm patterns were measured, and the motility differences for each antibiotic concentration were compared to the no-antibiotic control for each isolate.

Both chloramphenicol and tetracycline reduced swimming and swarming, although the reduction in swarming was greater than swimming at the same antibiotic concentration.  Conversely, kanamycin and streptomycin decreased bacterial swimming, but had little-to-no effect on limiting swarming.  In one isolate, kanamycin actually significantly increased the swarming phenotype compared to the no antibiotic control.  These results indicate that antibiotics affect the motility of MDR S. Typhimurium, and these observations are dependent on the antibiotic class, antibiotic concentration, isolate, and type of motility.  Future studies focused on identifying the mechanism(s) required for the observed motility differences, particularly the kanamycin-enhanced swarming, will help ascertain how different antibiotics can either positively or negatively influence this virulence factor in MDR Salmonella.


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