Antibiotic consumption is a major driver of antibiotic resistance in calves raised on Italian cow-calf beef farms.

Although its importance, little information is available on antibiotic-resistance in cow-calf beef farms. This study aimed to determine prevalence and risk factors for antibiotic-resistant organisms in this livestock system. Fifty-four farms from Central Italy were included to assess the presence of antibiotic-resistant indicator Escherichia coli and of ESBL and/or AmpC-producing E. coli (ESBL/AmpC-EC) in calves. Antimicrobial usage (AMU) was recorded, and farm-related variables were collected through questionnaires. Potential risk factors were tested using a mixed-effects logistic regression model. The presence of resistant-E. coli was recorded in 75.9% of farms (95% confidence interval [CI]: 62.4-86.5) with resistance to tetracyclines, sulfonamides, penicillins, and fluoroquinolones as the most frequent. The prevalence of farms positive for ESBL/AmpC-EC was 35.2% (95% CI: 22.7-49.4). AMU on the farms originating a resistant-E. coli was higher than that on the farms originating a susceptible-E. coli. The same difference was found for the consumption of beta-lactams (beta-DCD/year) and AMU via the parenteral route, which resulted also associated with the presence of ESBL/AmpC-EC. Farms with higher beta-DCD/year had an increased risk of being positive for resistant-E. coli, whereas farms with higher overall AMU had an increased risk for ESBL/AmpC-EC presence. Among farm-related factors, only farm size was associated with the presence of ESBL/AmpC-EC (odds ratio: 5.8, 95% CI: 1.3-26.3). Our findings highlight a reduction of the risk of ESBL/AmpC-EC in small cow-calf farms, and a strong association between AMU and antibiotic-resistance. Antibiotic stewardship programs are needed to improve the health status of cow-calf farms and ensure their long-term sustainability.

Association between pigs with high caecal Salmonella loads and carcass contamination.

Contaminated pork is a significant source of foodborne Salmonella infections. Pork is contaminated at the slaughterhouse; however, the mechanisms driving Salmonella contamination of carcasses are still poorly understood. The aim of this study was to investigate whether the amount of Salmonella carried by slaughtered pigs in their guts has an influence on carcass contamination. On that account, we tested whether the number of carcasses contaminated during a slaughter day was associated with the prevalence of highly contaminated pigs (HCP: Salmonella caecal loads ≥3log/g), or with the prevalence of pigs that simply carry Salmonella spp. in their guts. Three hundred and six pigs were sampled in a slaughterhouse from Central Italy. Salmonella loads in the caecum and on the carcass of each pig were estimated by the most probable number (MPN) technique. The overall prevalence of Salmonella was 34.64% and 7.19% for the caeca and carcasses, respectively. S. Derby and Salmonella enterica 4,[5],12:i:- were the most frequently isolated serovars. The prevalence of HCP was 11.44%. We found a higher number of contaminated carcasses on days of high prevalence of HCP than on days of low prevalence of HCP (p=0.0011). Conversely, carcass contamination did not vary with the prevalence of pigs that simply carried Salmonella spp. in their guts (p=0.7970). Therefore, the prevalence of HCP, but not the prevalence of pigs carrying Salmonella spp., was related to carcass contamination. Taken together, these findings suggest that reduction of Salmonella loads in the guts of slaughtered pigs would result in fewer contaminated carcasses, and consequently, help to minimise the risk of human infection due to the consumption of contaminated pork.