Submitted to: Journal of Veterinary Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2011
Publication Date: 3/8/2011
Citation: Brunelle, B.W., Bearson, S.M., Bearson, B.L. 2011. Salmonella enterica serovar Typhimurium DT104 invasion is not enhanced by sub-inhibitory concentrations of the antibiotic florfenicol. Journal of Veterinary Science and Technology. 2:104. Available: http://omicsonline.org/2157-7579/2157-7579-2-104.php. Interpretive Summary: Salmonella is the most prevalent foodborne bacterial pathogen in the United States with an estimated 1.4 million cases in humans per year and a projected annual health care cost of $2.6 billion. Over the past 20+ years, the number of cases in humans and animals due to antibiotic-resistant Salmonella has increased. Isolates of Salmonella enterica serovar Typhimurium DT104 are resistant to 5 or more antibiotics and have been associated with enhanced virulence in livestock and humans. S. Typhimurium DT104 is resistant to florfenicol, which is an antibiotic used to treat respiratory disease in cattle and swine. Because sub-inhibitory doses of antibiotics may enhance virulence, the effect of florfenicol on S. Typhimurium DT104 invasion was evaluated. Cellular invasion assays and gene expression experiments were performed, and the results demonstrate that invasion is not enhanced in isolates of S. Typhimurium DT104 after exposure to sub-inhibitory concentrations of florfenicol. Since food-producing animals (such as cattle and swine) can be asymptomatic carriers of Salmonella, this study provides important information for the livestock industry as it suggests that the treatment of one problem (respiratory illness) will not exacerbate a second and independent issue (S. Typhimurium DT104 in carrier animals).
Technical Abstract: The incidence of multi-drug resistant Salmonella has increased globally over the past several decades. Isolates of Salmonella enterica serovar Typhimurium DT104 are resistant to five or more antibiotics, including florfenicol, and have been associated with enhanced virulence in livestock and humans. Because sub-inhibitory concentrations of some antibiotics have been found to modulate invasion in certain bacteria under specific conditions, the effect of florfenicol on S. Typhimurium DT104 invasion was evaluated. Cellular invasion assays and gene expression analyses demonstrated that isolates of S. Typhimurium DT104 did not have enhanced invasion after exposure to sub-inhibitory concentrations of florfenicol. These results suggest that cattle and swine can be treated with florfenicol for respiratory illness without exacerbating Salmonella Typhimurium DT104 in asymptomatic carrier animals.