Emergence of chromosome borne colistin resistance gene, mcr-1 in clinical isolates of Pseudomonas aeruginosa

Abstract

Background: Transmissible colistin resistance gene, mcr-1 has breached the last line of defence against infections caused by carbapenem-resistant Enterobacteriaceae. In last few years, emergence of plasmid and chromosome borne mcr-1 gene in Enterobacteriaceae has been reported in several countries. Pseudomonas aeruginosa is a major contributor of nosocomial infections and excessive antibiotic usage against it has led to emergence of multidrug resistant strains. The colistin resistance in P. aeruginosa is reported to be adaptive in nature. Till date, there is no report of chromosome borne mcr-1 gene in P. aeruginosa. Here, we report the emergence of chromosome borne mcr-1 gene in four colistin resistant Pseudomonas aeruginosa clinical isolates. Methods and materials: A total of 1000 gram negative isolates were collected from clinical samples and identified using automated Vitek MS system (BioMerieux, France). Antibiotic susceptibility testing according to EUCAST guidelines revealed that 40 isolates were colistin resistant out of which 5 were P. aeruginosa. Screening of mcr-1 and other carbapenemases (blaNDM, KPC and OXA48) was done by PCR. Clonal lineage profiling of mcr-1 positive isolates was performed by PFGE. Transmissibility of mcr-1 gene was analyzed by conjugation using Escherichia coli J53 as recipient. Gene localization study was done using Southern hybridization. Results: Out of the 5 colistin resistant P. aeruginosa, 4 isolates (CRL-1, CRL-10, CRL-11 and CRL-12) harboured mcr-1 as confirmed by PCR and sequencing. The gene blaNDM-1 was present in one isolate (CRL-1) while KPC and OXA8 were not detected. Clonal lineage profiling revealed that 3 isolates CRL10, CRL11, CRL 12 were clonally related while CRL1 was unrelated. Conjugation experiment did not yield any transconjugants. The mcr-1 gene was located on chromosome in all four isolates. We probed for the presence of ISApl1 element upstream and downstream of mcr-1 in these isolates but it was not detected. Conclusion: This is, to the best of our knowledge, the first report about emergence of mcr-1 in P. aeruginosa from India and the gene has been stabilized on the chromosome. The transmission of mcr-1 gene from Enterobacteriaceae to other Gram negative bacteria and its co-existence with blaNDM-1 indicates a grim situation, a situation similar to the pre-antibiotic era.