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J. Dairy Sci. 2009. 92:4218-4228. doi:10.3168/jds.2008-1493
© 2009 American Dairy Science Association ®
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Introduction of new multidrug-resistant Salmonella enterica strains into commercial dairy herds

B. Adhikari*, T. E. Besser{dagger}, J. M. Gay*, L. K. Fox*, M. A. Davis{dagger}, R. N. Cobbold{ddagger}, A. C. Berge*, R. McClanahan* and D. D. Hancock*,1

* Agricultural Animal Health Program, Field Disease Investigation Unit, Department of Veterinary Clinical Sciences, and
{dagger} Department of Veterinary Microbiology and Pathology, Washington State University, Pullman 99164
{ddagger} School of Veterinary Science, The University of Queensland, Brisbane, Queensland 4072, Australia

1 Corresponding author: hancock{at}wsu.edu

A longitudinal observational study of 59 dairy herds was conducted in Washington State to estimate the rate of introduction of new multidrug-resistant (MDR) Salmonella enterica strains onto commercial dairy herds. Samples were collected on these herds over 7 visits separated by intervals of 2 to 4 mo over a period of 15 to 21 mo. Samples were cultured for Salmonella spp. and serogroup, serovar, and antimicrobial susceptibility patterns were identified for MDR Salmonella isolates. Fingerprinting generated by pulsed-field gel electrophoresis (PFGE) using XbaI restriction enzyme digestion generated genotyping profiles for all MDR isolates identified in the study. The rate of new MDR Salmonella strain introduction was 0.9 per herd-year (95% confidence interval: 0.6–1.4). The rates for the most commonly introduced MDR Salmonella serovars were 0.4/herd-year for Typhimurium, 1.2/herd-year for Newport, and 0.1/herd-year for Dublin. Thirty-three of 59 herds (56%) had at least one new MDR Salmonella introduction during the study period. The number of new MDR Salmonella strains acquired by dairy herds ranged from zero to 8. Thirteen of the 59 herds had a history of clinical salmonellosis. Among these 13 herds, 6 herds acquired new MDR Salmonella strains, although these strains were different than historical clinical strains. These data indicate that acquisition of new MDR Salmonella strains by dairy herds was a common event in participating herds, although the number of strains introduced varied greatly among herds.

Key Words: multidrug-resistant Salmonella • dairy farm • incidence rate • introduction


Related articles in JDS:

The role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant Salmonella
B. Adhikari, T. E. Besser, J. M. Gay, L. K. Fox, M. A. Davis, R. N. Cobbold, A. C. B. Berge, and D. D. Hancock
JDS 2009 92: 4229-4238. [Abstract] [Full Text]  





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