The Nasal Microbiome of Sows in the Federal District of Brazil Has Revealed a Diverse Phenotypic Resistance Profile

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.