Emergence of mcr-1 plasmid-mediated colistin-resistant Escherichia coli isolates from seawater

•Colistin resistance support was determined among isolates from seawater of Algiers coast.•From 246 isolates resistant to colistin, mcr-1 gene was identified in 2 E. coli strains.•MIC for colistin was corresponding to 4 μg/mL for M49 and 8 μg/mL for M78.•The two E. coli strains belonged to ST23 for M49 and ST115 for M78.•The mcr-1 gene was present on a non-conjugative plasmid in the two strains. Colistin is currently regarded as one of the ‘last-resort’ antibiotics used for the treatment of critical infections caused by multidrug-resistant Gram-negative pathogens. Recently, there have been numerous reports of the emergence of a transferable plasmid-mediated colistin resistance gene, mcr-1 in patients, animals, food, and environment. Here, we characterize the support of colistin resistance among environmental isolates collected from seawater of Algiers coast. Our study was carried out on 246 isolates resistant to colistin (MIC > 2 μg/L). The mcr-1 gene was identified in only two isolates; M49 and M78. The two strains were identified as Escherichia coli and were non-susceptible to amoxicillin, ticarcillin, piperacillin, gentamicin, nalidixic acid, tigecycline, tetracycline, trimethoprim-sulfamethoxazole and colistin. For the latter, isolates M49 and M78 showed MIC values of 4 μg/mL and 8 μg/mL, respectively. Only the strain M78 was intermediary resistant to tobramycin. The two E. coli strains belonged to two different sequence types (STs): ST23 for M49 and ST115 for M78. The mcr-1 gene was present on a non-conjugative plasmid in the two strains.