Maurício Macedo Rodrigues

Antimicrobial resistance (AMR) is a major public health concern influenced by antimicrobial use (AMU) in animal production systems. In swine, metaphylactic treatments may contribute to the emergence and dissemination of resistance genes. In this study, we isolated bacteria from the nasal cavities of 50 sows across 10 farms in the Federal District, Brazil. A total of 132 bacterial isolates were obtained and tested for phenotypic resistance to 23 antimicrobials using the disk diffusion method. Resistance was detected against all tested antimicrobials, with an overall resistance rate of 55.6% (1605/2888 tests). The highest resistance rates were observed for bacitracin (92.4%) and penicillin (79.2%), while lower resistance rates were found for aminoglycosides. Most isolates exhibited multidrug resistance to 7–9 classes of antimicrobials, including strains of Staphylococcus, Escherichia coli, and Klebsiella—all of which are relevant in the context of One Health. Actinobacillus suis showed the highest resistance levels among all identified species. AMR was positively correlated with both the duration and the number of antimicrobial agents used in feed, reinforcing the need for prudent AMU practices. The use of autogenous vaccines against Pasteurella multocida was associated with reduced lung lesions, underscoring the value of vaccination in disease control. AMR surveillance programs may benefit from including bacterial colonizers from the microbiota, though further studies are necessary to better understand the resistance dynamics of these commensals.

Antimicrobial resistance is a universal threat and is leading to a new awareness of antimicrobial use. The colonization of tissues by some microorganisms carrying resistance genes may pose a risk of spreading resistance to pathogens. Antimicrobials may induce an unstable microbiome that compromises the animal's immunity. Indeed, dysbiosis has been linked to many alterations in the immune response. Here, we isolated bacterial colonizers from the nasal microbiota of sows to describe the phenotypic resistance profile on different health managements. One hundred and thirty-two strains isolated from 50 nasal swabs collected from sows were tested against up to 23 antimicrobial agents by disk diffusion. Overall, the nasal communities showed 55% antimicrobial resistance (1605/2888 tests). Resistance was detected for all tested antimicrobials. The antimicrobial showing higher rate of resistance was bacitracin (92%), while the lowest was found in the aminoglycosides. Actinobacillus suis was one of the species with highest rate of resistance. The time and number of drugs used in feed influenced the resistance rate in the isolates. Vaccination was confirmed as a strategic protocol for disease control Studies on antimicrobial resistance in commensals may allow the identification of microorganisms to be used in surveillance and may constitute a tool for evaluating strategies to reduce antimicrobial use in pig herds.