Identification of colistin resistance gene origin in Escherichia coli isolated from migratory bird

Abstract

Introduction: As antimicrobial resistance is becoming a major threat to global health, colistin remains as one of the very few antibiotics that can still be effectively used against multi-drug resistant bacteria. However, an outbreak of plasmid-mediated colistin resistance, conferred by mcr-1 gene, was recently reported. Since the mcr-1 plasmids can be transferred between different species of bacteria, it causes concern of the emergence of bacteria resistant to all known antibiotics. Therefore, to identify and understand the mechanisms of mcr-1 spread is crucial for reducing fatalities caused by untreatable bacterial infections. Aim: To identify the origin of mcr-1 from E. coli isolated from faeces of Larus argentatus in Kaunas city dump. To the best of our knowledge, it is the first known occurrence of mcr-1 in Lithuania. Materials and Methods: To ensure that the mcr-1 is located in a plasmid, it was transferred to another strain via conjugation. PCR was performed to confirm the presence of mcr-1 and to find other antibiotic resistance genes in the plasmid. NCBI GenBank Database was screened for occurrences of mcr-1 gene using BLAST (100% identity and coverage cut-off). Potential plasmids were evaluated by restriction analysis. Results: The mcr-1 was successfully transferred into E. coli K-12 laboratory strain, proving that it is located in a plasmid. Any other antibiotic resistance genes were not found in the plasmid. 143 complete plasmid sequences from NCBI GenBank database contained identical mcr-1 sequence. By data acquired from restriction analysis of the extracted target plasmid, we can conclude, that it belongs to a group of 23 highly similar plasmids. Conclusion: The mcr-1 gene in E. coli isolated from migratory bird was found to be located in a plasmid widely spread across the world and shared between both animal vectors and human hospital patients