Otter fecal enterococci as general indicators of antimicrobial resistance dissemination in aquatic environments

Antimicrobial resistance is an emerging worldwide concern, as the use of antibiotics is crucial for human and animal health protection. Evaluations of the antimicrobial susceptibility of enteric microbiota can be used as an indicator of resistance dispersion in the environment. Commensal intestinal bacteria, such as Enterococcus spp., often act as reservoirs for antimicrobial resistance determinants and may allow gene transfer to animal or human pathogens present in the same habitats, including contaminated water. As contact between wild animals and human and domestic animal populations is increasing, the potential for dissemination of resistant pathogens to wildlife can be considered an emerging problem.This study aimed to confirm the potential of the intestinal commensal bacteria of otters as a model for assessing antimicrobial resistance dissemination in the environment. We evaluated the presence of antimicrobial-resistant enterococci in spraints from Eurasian and Neotropical otters, collected in Portugal and Brazil during 2015 and 2016 in different climatic seasons. We isolated Enterococcus spp., and then determined their clonal diversity and antimicrobial resistance profiles.The bacterial collection studied revealed high genomic diversity, ensuring its representativeness regarding the diversity of enterococci eliminated to the environment via otter spraints. Only one isolate, collected in Portugal, was susceptible to all the antimicrobial compounds tested, and the majority showed resistance to more than one antibiotic. We found high resistance levels to clindamycin in isolates from spraints collected in both countries, representing a particular concern for human health, as lincosamides are frequently used in cases of therapeutic failure. Antimicrobial resistance was higher in enterococci obtained from otter spraints collected in Brazil. However, significant correlations between antimicrobial resistance to individual compounds and country were only observed for Enrofloxacin and Vancomycin, which may be due to enrofloxacin use in animal production near the sample areas, particularly in poultry and cattle farms.Our results confirm the potential for these microorganisms to be used as indicators for monitoring antimicrobial resistance dissemination. These findings suggest that aquatic habitats occupied by otters may act as reservoirs of antimicrobial-resistant bacteria, the presence of which could impact human health through exposure to contaminated waters during fishing or recreational activities. Appropriate management and monitoring plans must be established to protect the environment and public health against the adverse effects of antibiotics, with this being particularly important in countries where antibiotics are increasingly being administered in veterinary settings.