Molecular and genome characterization of colistin-resistant Escherichia coli isolates from wild sea lions (Zalophus californianus).

Using molecular and whole-genome sequencing tools, we investigated colistin-resistant Escherichia coli isolates from wild sea lions. Two unrelated E. coli colistin-resistant isolates, ST8259 and ST4218, were identified, both belonging to the B2 phylogroup and different serotypes. Polymorphisms in PmrA, PmrB, and PhoQ proteins were identified, and the role of PmrB and PhoQ in contributing to colistin resistance was determined by complementation assays. However, the mutations characterized in the present study are not involved in colistin resistance, which have been described in E. coli isolates from clinical settings. Therefore, the acquired mutations in pmrB and phoQ genes in resistance to colistin in bacteria related to marine environment animals are different. This work contributes to the surveillance and characterization of colistin resistance in Escherichia coli obtained from animals from aquatic environments.