Colistin-resistant Enterobacter kobei carrying mcr-9.1 and bla infecting a critically endangered franciscana dolphin (Pontoporia blainvillei), Brazil.

The emergence of mobile mcr genes mediating resistance to colistin is a critical public health issue that has hindered the treatment of serious infections caused by multidrug-resistant pathogens in humans and other animals. We report the emergence of the mcr-9.1 gene in a polymyxin-resistant extended-spectrum β-lactamase (ESBL)-producing Enterobacter kobei infecting a free-living franciscana dolphin (Pontoporia blainvillei), threatened with extinction in South America. Genomic analysis confirmed the presence of genes conferring resistance to clinically relevant β-lactam [bla , bla , bla and bla ], aminoglycoside [aac(3)-IIa, aadA1, aph(3'')-Ib and aph(6)-Id], trimethoprim [dfrA14], tetracycline [tetA], quinolone [aac(6')-Ib-cr and qnrB1], fosfomycin [fosA], sulphonamide [sul2] and phenicol [catA1 and catB3] antibiotics. The identification of mcr-9.1 in a CTX-M-15-producing pathogen infecting a critically endangered animal is of serious concern, which should be interpreted as a sign of further spread of critical priority pathogens and their resistance genes in threatened ecosystems.