The spread of bacteria resistant to last-resort antibiotics such as colistin throughout the food chain is a serious concern for public health. The poultry sector has responded by restricting colistin use and exploring alternative trace metals/copper feed supplements.

The expansion of mcr‐carrying bacteria is a well‐recognized public health problem. Measures to contain mcr spread have mainly been focused on the food–animal production sector. Nevertheless, the spread of MCR producers at the environmental interface particularly driven by the increasing population of gulls in coastal cities has been less explored. Occurrence of mcr‐carrying Escherichia coli in gull's colonies faeces on a Portuguese beach was screened over 7 months. Cultural, molecular and genomic approaches were used to characterize their diversity, mcr plasmids and adaptive features. Multidrug‐resistant mcr‐1‐carrying E. coli were detected for 3 consecutive months. Over time, multiple strains were recovered, including zoonotic‐related pathogenic E. coli clones (e.g. B2‐ST131‐H22, A‐ST10 and B1‐ST162). Diverse mcr‐1 genetic environments were mainly associated with ST2/ST4‐HI2 (ST10, ST131, ST162, ST354 and ST4204) but also IncI2 (ST12990) plasmids or in the chromosome (ST656). Whole‐genome sequencing revealed enrichment of these strains on antibiotic resistance, virulence and metal tolerance genes. Our results underscore gulls as important spreaders of high‐priority bacteria and genes that may affect the environment, food–animals and/or humans, potentially undermining One‐Health strategies to reduce colistin resistance.

Because of public health concerns, much greater scrutiny is now placed on antibiotic use in pets, especially for antimicrobial agents that have human analogs. Therefore, this study aimed to characterize the phenotypic and genotypic profiles of multidrug-resistant bacteria isolated from nasal swabs samples taken from a one-year-old male Serra da Estrela dog with rhinorrhea that was treated with amikacin. An extended-spectrum β-lactamases (ESBL) Klebsiella pneumoniae was isolated in the first sample taken from the left nasal cavity of the dog. Seven days later, methicillin-resistant (MRSP) Staphylococcus pseudintermedius was also isolated. Nevertheless, no alterations to the therapeutic protocol were performed. Once the inhibitory action of the antibiotic disappeared, the competitive advantage of the amikacin-resistant MRSP was lost, and only commensal flora was observed on both nasal cavities. The genotypic profile of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae revealed the same characteristics and close relation to other strains, mainly from Estonia, Slovakia and Romania. Regarding MRSP isolates, although resistance to aminoglycosides was present in the first MRSP, the second isolate carried aac(6′)-aph(2″), which enhanced its resistance to amikacin. However, the veterinary action was focused on the treatment of the primary agent (ESBL K. pneumoniae), and the antibiotic applied was according to its phenotypic profile, which may have led to the resolution of the infectious process. Therefore, this study highlights the importance of targeted therapy, proper clinical practice and laboratory-hospital communication to safeguard animal, human and environmental health.