Contributions of insertion sequences conferring colistin resistance in Klebsiella pneumoniae

Background: Increasing colistin consumption is leading to expanding colistin resistance in Klebsiella pneumoniae worldwide, but particularly in Asia. Epidemiological studies indicate a link between specific insertion sequences (ISs) and colistin resistance; however, proof of a colistin-IS correlation is lacking. Objectives: Colistin-resistant mechanisms, and in vitro and in vivo efficacies of colistin against K. pneumoniae with ISs were investigated. Methods: Colistin-resistant genes, including mcr-1 gene, were detected in 49 colistin-and carbapenem-resistant K. pneumoniae isolates. crrCAB genetic environments were analysed using whole-genome sequencing and polymerase chain reaction (PCR) mapping. Identified ISs were cloned into pRK415 vectors and investigated for potential contributions to colistin resistance. A Caenorhabditis elegans model was employed for in vivo analysis. Results: mgrB gene alterations (32/49, 65.3%) were identified as the major colistin-resistant mechanism, followed by variations in crrB (57.1%), pmrB (32.7%), phoQ (20.9%), pmrA (16.3%) and phoP (8.2%) genes. Furthermore, 21 of the 49 tested isolates (42.9%) contained the IS elements, ISKpn26, IS Ecp1, IS10R, IS903B or ISKpn14 in mgrB or in the surrounding region of crrCAB, indicating an association between these ISs and colistin resistance. The frequencies of colistin resistance significantly increased in colistin-susceptible K. pneumoniae laboratory strains, with plasmids carrying different ISs from clinical strains. In vivo analysis revealed that K. pneumoniae harboring ISKpn26 was associated with decreased lifespan during colistin treatment, leading to an increased risk for colistin treatment failure. Conclusions: These findings indicate a correlation between diverse ISs and colistin resistance in K. pneumoniae and confirm a role for ISs in colistin treatment. (C) 2020 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.