Chlortetracycline enhances tonsil colonization and fecal shedding of multidrug-resistant Salmonella enterica serovar typhimurium DT104 without major alterations to the porcine tonsillar and intestinal microbiota
Citation
Holman, D.B., Bearson, B.L., Allen, H.K., Shippy, D.C., Loving, C.L., Kerr, B.J., Bearson, S.M.D., Brunelle, B.W. (2019). Chlortetracycline enhances tonsil colonization and fecal shedding of multidrug-resistant Salmonella enterica serovar typhimurium DT104 without major alterations to the porcine tonsillar and intestinal microbiota. Applied and Environmental Microbiology, [online] 85(4), http://dx.doi.org/10.1128/AEM.02354-18
Plain language summary
Salmonella spp. are an important cause of foodborne illness in North America, and pork products are associated with sporadic cases and outbreaks of human salmonellosis. Isolates of Salmonella may be resistant to multiple antibiotics, and infections with multidrug-resistant (MDR) Salmonella spp. are more difficult to
treat, leading to increased hospitalization rates. Swine operations commonly use antimicrobials, such as chlortetracycline, to prevent/treat infections, which may have collateral effects on pig microbial populations. Therefore, in this study, post-weaned pigs were challenged with a strain of MDR Salmonella and given a therapeutic dose of chlortetracycline in their feed prior to being challenged. The ileal, cecal, and fecal tonsil microbial community (microbiota) of the pigs was characterized as well the concentration of Salmonella in these samples. There was no significant effect of either Salmonella or chlortetracycline on any of the microbiota; however, pigs that received chlortetracycline had significantly higher concentrations of Salmonella in their tonsils. Consequently, pigs unknowingly colonized with MDR Salmonella spp. and receiving chlortetracycline for an unrelated infection may be at a greater risk for disseminating MDR Salmonella spp. to other pigs and to humans through environmental or pork product contamination.
Abstract
Salmonella spp. are estimated to cause 1.2 million cases of human foodborne illness each year in the United States, and pigs can often be asymptomatically colonized with Salmonella spp. (>50% of farms). Recent reports state that 18.3% of Salmonella enterica serovar Typhimurium isolates are resistant to ≥3 antimicrobial classes, and multidrug-resistant (MDR) strains are associated with an increased hospitalization rate and other complications. Chlortetracycline is commonly used in swine production to prevent/treat various diseases; therefore, chlortetracycline treatment of pigs unknowingly colonized with MDR Salmonella may have collateral effects on Salmonella spp. (and other gut bacteria). In this study, we determined the effect of in-feed chlortetracycline (400 g/ton) on shedding and colonization of pigs challenged with the MDR S. Typhimurium strain DT104 (n = 11/group). We also assessed the impact on the fecal microbiota over the 12-day experimental period and on the ileum, cecum, and tonsil microbiota at 7 days postinoculation (dpi). In MDR S. Typhimurium-inoculated pigs, chlortetracycline administration significantly increased fecal shedding at 2 dpi (+1.4 log 10 CFU/g; P < 0.001) and enhanced tonsil colonization (+3.1 log 10 CFU/g; P < 0.001). There were few major alterations detected in the gut or tonsillar microbiota of pigs treated with MDR S. Typhimurium and/or chlortetracycline. The tonsillar transcriptome was largely unaffected despite increased colonization by MDR S. Typhimurium following inoculation of the chlortetracycline-treated pigs. These results highlight the idea that chlortetracycline administration can enhance shedding and colonization of MDR S. Typhimurium in pigs, which could increase the risk of environmental dissemination of MDR Salmonella strains.