Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/24/2007
Publication Date: 1/1/2008
Citation: Edrington, T.S., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2008. Prevalence of multi-drug resistant Salmonella on commercial dairies utilizing a single heifer raising facility. Journal of Food Protection. 71(1):27-34. Interpretive Summary: Dairy cattle may contain the bacteria Salmonella that can make people sick. In some instances these Salmonella are resistant to several of the antibiotics used to kill them. We sampled calves, heifers, healthy and sick cows on four dairies and looked for resistant Salmonella. Results of this experiment showed that althought resistant Salmonella are not very common in dairy cattle, it is most often found in young calves and sick cows.
Technical Abstract: The objectives of the current research were two-fold: 1) Determine the prevalence of multiple drug resistant (MDR) Salmonella in the various classes of dairy cattle; and 2) Determine if co-mingling of calves from multiple farms at a heifer feedlot serves as a transmission vector for Salmonella back to the dairy farm. Four large commercial dairies in the southwestern United States were sampled in October 2005 and again in March 2006. Fecal samples were collected from hutch calves, 12 and 24 month old heifers, lactating cows, dry cows, and cattle in the sick/fresh pen and cultured using brilliant green agar with novobiocin, for overall Salmonella prevalence (BGA) or tetracycline, for MDR Salmonella (BGA). Antimicrobial susceptibility testing was conducted using the NARM’s testing panel and a portion of the isolates serotyped. Salmonella prevalence ranged from 0 to 96% positive, with the highest incidence observed in the hutch calves and cattle in the sick/fresh pen. Twenty-eight different serotypes were identified with serotype Reading accounting for the majority of isolates cultured on BGA. Nearly all isolates cultured on BGA and screened for antibiotic resistance were pan susceptible, whereas over half (64%) of the isolates cultured on BGA were MDR. Forty isolates displayed the ACSSuT resistance pattern and 36 isolates the MDR-AmpC pattern. The incidence of Salmonella was low in all heifers and only one MDR isolate was cultured (from a 12 month old heifer), suggesting the risk of transmission of Salmonella from the heifer feedlot back to the dairy is low. Results of this research suggest the incidence of MDR Salmonella, found primarily in hutch calves and cattle in the sick/fresh pen, is low in comparison to overall Salmonella prevalence.