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Applied and Environmental Microbiology, January 2008, p. 345-351, Vol. 74, No. 2
0099-2240/08/$08.00+0     doi:10.1128/AEM.02076-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Salmonella enterica Burden in Harvest-Ready Cattle Populations from the Southern High Plains of the United States

David J. Kunze,¹ Guy H. Loneragan,^1* Tammy M. Platt,¹ Mark F. Miller,² Thomas E. Besser,³ Mohammad Koohmaraie,⁴ Tyler Stephens,^2, and Mindy M. Brashears²

Feedlot Research Group, Department of Agricultural Sciences, West Texas A&M University, Canyon, Texas,¹ Department of Animal and Food Sciences, Texas Tech University, Lubbock, Texas,² College of Veterinary Medicine, Washington State University, Pullman, Washington,³ USDA-U.S. Meat Animal Research Center, Clay Center, Nebraska⁴

Received 11 September 2007/ Accepted 3 November 2007

Our objectives were to quantify the Salmonella enterica burdens in harvest-ready cattle and to identify specific at-risk populations of cattle most likely to harbor multiply resistant S. enterica. Hide swabs were collected in abattoirs from three cohorts of cattle (feedlot origin cattle that had achieved desirable harvest characteristics and dairy- and beef-type cows harvested because of poor productivity). Feces were collected from two cohorts housed in feedlots (cattle that had achieved desirable harvest characteristics and animals identified for salvage recovery because of poor productivity). Facilities were visited on four occasions over a 12-month period. Salmonella enterica isolates were recovered, and organisms were quantified using standard microbiological methodologies. Susceptibility to antimicrobial drugs and serotype were determined for one S. enterica isolate per sample. Salmonella enterica was recovered from 55.6% of 1,681 samples. The prevalences on hides and in feces were 69.6% and 30.3%, respectively. The concentrations of S. enterica organisms averaged (as determined by the most probable number technique) 1.82 log₁₀/100 cm² of hides and 0.75 log₁₀/g of feces. None of the isolates recovered from cattle that had achieved desirable harvest characteristics were resistant to four or more drugs. For isolates recovered from animals with poor productivity characteristics, 6.5% were resistant to four or more drugs. Twenty-two serovars were identified, with the most common being Salmonella enterica serovar Anatum (25.5%), Salmonella enterica serovar Montevideo (22.2%), and Salmonella enterica serovar Cerro (12.5%). High-level resistance, i.e., resistance to four or more drugs, was clustered within a few relatively uncommon serovars. These results demonstrate that even though S. enterica isolates are readily recoverable from harvest-ready cattle, multiply resistant variants are rare and are associated with specific serovars in cattle harvested because of poor productivity characteristics.

Published ahead of print on 16 November 2007.

Present address: Alberta Agriculture and Food, Lethbridge, Alberta, Canada.