Submitted to: Molecular Genetics of Bacteria and Phage
Publication Type: Abstract Only
Publication Acceptance Date: July 9, 2013
Publication Date: August 6, 2013
Citation: Bearson, B.L., Brunelle, B.W., Allen, H.K., Bayles, D.O., Stanton, T.B. 2013. The agricultural antibiotic carbadox induces generalized transducing phage in multidrug-resistant Salmonella enterica serovar Typhimurium DT104. Abstracts of the 2013 Molecular Genetics of Bacteria and Phages Meeting, August 6-10, 2013, Madison, Wisconsin. p. 95. Technical Abstract: Non-typhoidal Salmonella, a leading cause of U.S. foodborne disease and food-related deaths, often asymptomatically colonizes food-producing animals. In fact, >50% of U.S. swine production facilities test positive for Salmonella. The multidrug-resistant (MDR) Salmonella Typhimurium DT104 NCTC13348 contains five prophages in the genome that may be induced to produce phage under various environmental conditions, including antibiotic exposure. In this study, we investigated phage induction in MDR DT104 following exposure to carbadox, an antibiotic frequently used in the U.S. during the starter phase of swine production for performance enhancement and control of enteric diseases. A sub-inhibitory concentration of carbadox induced phage production in DT104, resulting in bacterial cell lysis and visible virions by EM. RNA-seq analysis of DT104 following carbadox exposure identified numerous genes from three of the five prophages (homologs of Gifsy-1, ST64B, and P22) with significantly increased expression, suggesting that multiple prophages were induced concurrently and that a phage induction hierarchy may exist. Genomic deletion of Gifsy-1, ST64B, and P22 prophage either alone or in combination resulted in decreased bacterial cell lysis following carbadox exposure, indicating that all three prophages were induced in wild-type DT104. Using a carbadox-induced phage lysate from DT104, we demonstrated genetic transfer of non-phage DNA to a recipient S. Typhimurium, including Salmonella genomic DNA and plasmid DNA conferring antibiotic resistance. Deletion of the P22 prophage eliminated carbadox-induced, phage-mediated gene transfer, indicating that the P22 prophage facilitates generalized transduction from DT104. Furthermore, a carbadox-induced phage lysate from a 'Gifsy-1 'ST64B double mutant (P22-like+) facilitated a >10-fold increase in gene transfer by transduction compared to wild-type DT104; this finding suggests that competition between phage production and phage-mediated, bacterial cell lysis may limit generalized transduction efficiency via P22 prophage from the wild-type DT104. Our research indicates that carbadox exposure of MDR DT104 induces different lytic and lysogenizing prophages and promulgates transduction of antibiotic resistance to susceptible Salmonella hosts. Further research is warranted to determine whether generalized transducing phage are induced as a collateral effect of carbadox administration in swine colonized with Salmonella.