ECOLOGY AND MOLECULAR EPIDEMIOLOGY OF ZOONOTIC BACTERIAL PATHOGENS ASSOCIATED WITH DAIRY FARMS
Location: Environmental Microbial and Food Safety Laboratory
Title: Antimicrobial resistance of Salmonella enterica isolated from bulk tank milk and milk filters in the United States
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 13, 2012
Publication Date: July 17, 2012
Citation: Van Kessel, J.S., Sonnier, J.L., Zhao, S., Karns, J.S. 2012. Antimicrobial resistance of Salmonella enterica isolated from bulk tank milk and milk filters in the United States. Meeting Abstract.
Salmonella isolates were recovered from bulk tank milk as part of the National Animal Health Monitoring System (NAHMS) Dairy 2002 and 2007 surveys. In-line milk filters were also tested in the 2007 survey. The objective of this study was to determine the prevalence of antimicrobial resistance among S. enterica isolates from bulk milk and milk filters in the NAHMS Dairy 2002 and 2007 surveys and to further characterize resistant isolates. Susceptibilities to 15 antibiotics were determined for 176 Salmonella isolates (26 serotypes) using an automated antimicrobial susceptibility system. Resistant isolates were screened by PCR for the presence of the extended-spectrum ß-lactamase (blaCMY) gene and class I integrons, and further characterized by Pulsed-Field Gel Electrophoresis (PFGE). Thirty isolates (17.0%) representing six serotypes [Newport (14/14), Dublin (7/7), Typhimurium (3/5), Kentucky (4/22), Anatum (1/13), and Infantis (1/2)] exhibited resistance to at least one antimicrobial agent. Twenty isolates (11.4%), including all 14 S. Newport, three S. Dublin, two S. Typhimurium, and one S. Infantis, displayed the typical multi-drug resistant, blaCMY+ (MDR-AmpC) phenotype which included resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline (ACSSuT), plus resistance to amoxicillin-clavulanic acid (AUG) and extended spectrum cephalosporins (ESCs). Five of the MDR-AmpC isolates carried class I integrons (2.8%). Two-enzyme (Xba I and Bln I) PFGE discerned clades within serotypes and, together with the resistance profiles identified strains that appeared to have persisted temporally and geographically. These results suggest that there is a low but appreciable risk of infection with multi-drug resistant Salmonella from consumption of non-pasteurized milk and dairy products.