Purpose
Colistin is classified by the World Health Organization (WHO) as a critically important and last-resort antibiotic for the treatment of infections caused by carbapenem-resistant bacteria. However, colistin resistance mediated by chromosomal mutations or plasmid-linked mobilized colistin resistance (
mcr
) genes has emerged.
Methods
Thirteen
mcr
-positive
Aeromonas
species isolated from water samples collected in Eastern Ghana were analyzed using whole-genome sequencing (WGS). Antimicrobial susceptibility was tested using the broth microdilution method. Resistome analysis was performed
in silico
using a web-based platform.
Results
The minimum inhibitory concentration (MIC) of colistin for all except three isolates was >4 µg/mL. Nine new sequence types were identified and whole-genome analysis revealed that the isolates harbored genes (
mcr-3
-related genes) that code for Lipid A phosphoethanolamine transferases on their chromosomes. BLAST analysis indicated that the amino acid sequences of the
mcr-3
-related genes detected varied from those previously reported and shared 79.04–99.86% nucleotide sequence identity with publicly available
mcr-3
variants and
mcr-3
-related phosphoethanolamine transferases. Analysis of the genetic context of
mcr-3
-related genes revealed that the genetic environment surrounding
mcr-3
-related genes was diverse among the different species of
Aeromonas
but conserved among isolates of the same species.
Mcr-3
-related-gene-IS-
mcr-3
-related-gene segment was identified in three
Aeromonas caviae
strains.
Conclusion
The presence of
mcr-3
-related genes close to insertion elements is important for continuous monitoring to better understand how to control the mobilization and dissemination of antibiotic resistance genes.