Tuesday, September 26, 2017 at 4:00pm to 5:00pm
Salmonella Epidemiology at the Preharvest Level: A Texas Perspective, from Feral Pigs to Dairy Cattle
Presented by Kevin Cummings, Associate Professor, Department of Population Medicine and Diagnostic Sciences, Cornell University
Salmonella is a leading cause of hospitalization and death among foodborne pathogens, and the incidence of human salmonellosis in the United States persists at its level of 10 years ago. Antimicrobial resistance among Salmonella isolates magnifies the problem, limiting treatment options and increasing the risk of therapeutic failure. The objectives of this presentation will be to review recent work in Texas to investigate epidemiologic aspects of Salmonella shedding among a wide range of animal reservoirs.
Feral pigs are one of the most abundant free-roaming ungulates in the United States, yet their role in the ecology and transmission of foodborne pathogens is poorly understood. We collected fecal samples from feral pigs in Texas from June 2013 through May 2015. The apparent prevalence of fecal Salmonella shedding via bacteriologic culture was 43.9% (194/442), with positive pigs originating from 50 of 64 sampled counties. High serotype diversity was evident among the isolates, and many of the detected serotypes are leading causes of human salmonellosis; the most common were Montevideo (10.0%) and Newport (9.1%). However, resistance to antimicrobial agents was rare. High prevalence of fecal Salmonella shedding among feral pigs throughout Texas suggests that this invasive wildlife species is an emerging threat to food safety in the United States.
We also investigated the role played by migratory waterfowl in the epidemiology of Salmonella, given their ability to travel long distances and their use of varied habitats. Fecal samples were collected from hunter-harvested waterfowl at four wildlife management areas (WMAs) along the Texas Gulf coast from September through November, 2016. In contrast to our findings with feral pigs, the apparent prevalence of fecal Salmonella shedding was only 0.5% (2/375). Although fecal contamination of agricultural fields or surface waters could serve as a potential source of zoonotic Salmonella transmission, waterfowl along the Gulf coast during the fall hunting season appear to pose minimal risk.
In our work with dairy cattle in Texas, we isolated Salmonella from 67.0% of environmental swab samples (236/352) collected from 11 dairy farms across the state. Isolates from the calf housing area and maternity pen were significantly more likely to be multidrug-resistant than isolates from other areas. Two isolates, serotyped as Salmonella Muenster, showed the discordant pattern of nalidixic acid susceptibility and intermediate susceptibility to ciprofloxacin. Whole-genome sequencing was performed in order to detect genes associated with quinolone resistance, and the plasmid-mediated qnrB19 gene was identified in both isolates. To our knowledge, this was the first report of plasmid-mediated quinolone resistance (PMQR) in Salmonella isolated from food animals or agricultural environments in the United States.