Identification of Escherichia coli and Salmonella enterica organisms with reduced susceptibility to ceftriaxone from fecal samples of cows in dairy herds.

OBJECTIVE: To estimate the relationship between therapeutic use of ceftiofur and recovery of Escherichia coli and Salmonella spp with reduced susceptibility to ceftriaxone from feces of dairy cattle. ANIMALS: 3,840 mature dairy cows on 50 dairy herds in Ohio. Procedures-Fecal samples were obtained from up to 100 mature dairy cows on each farm. Samples were screened for E coli and Salmonella spp with reduced susceptibility to ceftriaxone by use of selective media.
RESULTS: E coli with reduced susceptibility to ceftriaxone was recovered from 92% (46/50) of the herds and 60.9% (2,338/3,840) of cows. Salmonella spp were recovered from 44% (22/50) of the herds and 9.9% (382/3,840) of cows. No association was found between ceftiofur use and recovery of E coli with reduced susceptibility to ceftriaxone at the herd level. However, recovery of E coli with reduced susceptibility to ceftriaxone was more likely from cows in herds in which Salmonella spp were also recovered on the day of collection (odds ratio, 24.96; 95% confidence interval, 3.17 to 196.68) than from herds in which Salmonella spp were not recovered. Odds of recovery of E coli with reduced susceptibility to ceftriaxone from an individual cow increased 62% (odds ratio, 1.62; 95% confidence interval, 1.16 to 2.25) for every 454-kg increase in herd milk production. CONCLUSIONS AND CLINICAL RELEVANCE: No evidence was found that the use of ceftiofur on dairy farms increases the prevalence or dissemination of Salmonella spp or E coli with reduced susceptibility to ceftriaxone.