Antimicrobial resistance in Salmonella isolates from dairy cattle

Abstract

Salmonella is a common cause of food-borne illness. There is concern that antimicrobial resistance in human isolates is increasing and that a source of these resistant isolates is due to antimicrobial use in livestock. This project evaluated antimicrobial susceptibility of Salmonella isolated from dairy cattle and their environment. Salmonella isolates were collected from dairies in the midwest and northeast. Minimal Inhibitory Concentration (MIC) was measured for 14 antimicrobial agents. The majority of Salmonella isolates were susceptible to all drugs tested. There was no clear pattern of changing resistance during the one-year study period. The MIC resistance pattern of fecal and environmental samples was compared but there was not a strong agreement between the sample sources. Animal-level factors (age, treatment, health status) were analyzed for development of multi-drug resistance as well as resistance to other antimicrobial agents. Resistance was more common in pre-weaned calves and cattle with diarrhea and metabolic problems.