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Applied and Environmental Microbiology, August 2008, p. 5038-5046, Vol. 74, No. 16
0099-2240/08/$08.00+0     doi:10.1128/AEM.00409-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Characterization of Salmonella enterica serovar Heidelberg from Turkey-Associated Sources

National Farm Medicine Center, Marshfield Clinic Research Foundation, Marshfield, Wisconsin,¹ Department of Biology, University of Central Arkansas, Conway, Arkansas,² Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, Arkansas,³ Division of Animal and Food Microbiology, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland,⁴ Department of Veterinary and Microbiological Sciences, North Dakota State University, Fargo, North Dakota⁵

Received 18 February 2008/ Accepted 19 June 2008

Salmonella enterica serovar Heidelberg strains are frequently associated with food-borne illness, with recent isolates showing higher rates of resistance to multiple antimicrobial agents. One hundred eighty S. enterica serovar Heidelberg isolates, collected from turkey-associated production and processing sources, were tested for antimicrobial susceptibility and compared by pulsed-field gel electrophoresis (PFGE) and plasmid profile analysis. The potential for the transfer of resistance between strains was studied by conjugation experiments. PFGE analysis using XbaI digestion identified eight clusters (based on 90% similarity), with the largest containing 71% of the isolates. Forty-two percent of the isolates were resistant to at least 1 of the 15 antimicrobial agents tested, and 4% of the isolates were resistant to 8 or more antimicrobial agents. Resistances to streptomycin (32%), tetracycline (30%), and kanamycin (24%) were most commonly detected. Interestingly, the XbaI PFGE profiles of selective multidrug-resistant strains (n = 22) of S. enterica serovar Heidelberg from turkey-associated sources were indistinguishable from the predominant profile (JF6X01.0022) detected in isolates associated with human infections. These isolates were further differentiated into seven distinct profiles following digestion with the BlnI enzyme, with the largest cluster comprising 15 isolates from veterinary diagnostic and turkey processing environments. Conjugation experiments indicated that resistance to multiple antimicrobial agents was transferable among strains with diverse PFGE profiles.

Published ahead of print on 27 June 2008.