Characterization of Escherichia coli isolates obtained from cetaceans from a One Health perspective

Abstract

Marine mammals, such as cetaceans, can act as reservoirs of Escherichia coli strains carrying virulence factors and antimicrobial resistance genes, often associated with anthropogenic pollution. From the One Health approach, these species are valuable sentinel organisms for assessing the state of the marine ecosystem and the risks that microbiological contaminationmay pose to environmental, animal and human health. This study aimed to characterize E. coli isolates obtained from 20 fecal samples collected from different cetacean species, including: killer whale (Orcinus orca), Atlantic bottlenose dolphin (Tursiops truncatus), common porpoise (Phocoena phocoena), common dolphin (Delphinus delphis), striped dolphin (Stenella coeruleoalba), fin whale (Balaenoptera physalus), and sperm whale (Physeter macrocephalus). Samples were cultured on MacConkey agar and selective media for coliforms. E. coli was successfully isolated in 5 of the 20 samples, corresponding to a 25% isolation rate. DNA was extracted from the isolates and PCR assays were conducted to detect virulence and antimicrobial resistance-associated genes. Among the positive isolates, the following genes were identified: rfb (marker of serogroup O157:H7), aggR (associated with the enteroaggregative E. coli pathotype), vat (linked to uropathogenic strains), and blaCTX-M (involved in the production of extended-spectrum β-lactamases, ESBL). The detection of these genes in cetaceanderived isolates highlights the relevance of these marine species as indicators of fecal pollution and as potential carriers of zoonotic pathogens and antimicrobial resistance elements. These findings emphasize the importance of continued environmental surveillance and further investigation into the role of marine wildlife in the dissemination of microbial threats.