Cross-Sectional Study on Zoonotic Bacteria Carriage by Small Ruminants from Portugal's Central Region

Zoonotic bacteria, namely Campylobacter spp., Escherichia coli, Salmonella spp. and Staphylococcus aureus, are commonly implicated in human infections and can be transmitted from animals to humans through direct contact, the environment or the food chain. The emergence of antimicrobial resistance in these zoonotic bacteria, namely extended spectrum β-lactamases (ESBLs)-producing strains of E. coli and methicillin-resistant S. aureus (MRSA), has become a public health concern worldwide. This study aimed to determine the prevalence of fecal carriage of Campylobacter spp., Salmonella spp. and ESBL-producing strains of E. coli, as well as nasal carriage of MRSA, and to identify risk factors associated with the presence of these zoonotic bacteria in small ruminants from Portugal's Central Region. A total of 732 animals, of which 432 sheep and 300 goats from 122 farms were sampled. Zoonotic enteric bacteria were isolated from individual fecal samples, while MRSA were isolated from pooled nasal swabs collected from each farm. Bacteria were isolated according to standard microbiological methods. The overall prevalence of Campylobacter spp. and Salmonella spp. at the animal level was 15.6% and 8.3%, respectively, with significantly higher prevalence in sheep (19.0% and 12.7%) compared to goat (10.7% and 2.0%). Presumptive ESBL-producing strains of E. coli was isolated from 5.2% of the animals. Presumptive MRSA was isolated from 5.7% of the farms. A cluster analysis was performed to identify farm clusters with similar characteristics based on the isolation of Campylobacter spp., Salmonella spp., presumptive ESBL-producing E. coli, and presumptive MRSA. Farms were grouped into three clusters: "Resistant", "Campylobacter" and "Salmonella". The likelihood of farms belonging to "Campylobacter" and "Salmonella" clusters in comparison to "Resistant" cluster was associated with animal species, farm location, and farmer' practices regarding antibiotic use. This study reinforces the role of small ruminants as asymptomatic reservoirs of Campylobacter spp., Salmonella spp., E. coli and S. aureus and confirms, for the first time, their role as carriers of presumptive antibiotic-resistant zoonotic bacteria in Portugal's Central Region.