Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2021

Strain-specific risks and mechanisms of colistin resistance among K. pneumoniae clinical isolates (#69)

Kelly L Wyres 1 , Taylor Harshegyi 1 , Louise M Judd 1 , Abhilasha Karkey 2 , Steve Baker 3 , Kathryn E Holt 1 4
  1. Department of Infectious Diseases, Monash University, Melbourne, VIC, Australia
  2. Oxford University Clinical Research Unit, Kathmandu, Nepal
  3. Cambridge Institute of Therapeutic Immunology & Infectious Disease, University of Cambridge, Cambridge, United Kingdom
  4. London School of Hygiene and Tropical Medicine, London, United Kingdom

Klebsiella pneumoniae is a major cause of bacterial healthcare-associated infections for which the rate of multi-drug resistant and carbapenem-resistant isolates is increasing globally. In some regions >50% of K. pneumoniae clinical isolates are carbapenem-resistant and as a result there is increasing reliance on last-line antimicrobials such as colistin. Unfortunately, this has been accompanied by an increase in reports of colistin-resistance conferred through de novo mutations that emerge during drug exposure. However, it remains unclear if all K. pneumoniae are subject to the same risk for resistance and/or the same resistance mechanisms.

 

Here we used an in vitro experimental evolution approach to compare the rates of emergence of colistin resistance among 8 independent K. pneumoniae clonal groups (phylogenetic lineages, n=3 isolates each). Isolates were cultured in sequentially increasing concentrations of colistin (0.06-8µg/ml, n=9 replicates each, plus two controls without colistin) and surviving culture lines were subjected to high-throughput sequencing on the Illumina platform.

 

The proportion of cultures surviving at 8µg/ml colistin varied substantially between isolates (0-100%) and there was evidence of clonal group-specific differences. Resistance conferring mutations were identified for 70/81 (86%) mutants, among which the most common was disruption of the mgrB gene (47% isolates), which is known to result in lipopolysaccharide modifications that prevent colistin binding. However, the proportion of mutants harbouring mgrB mutations differed between clonal groups (14-83%), as did the mechanism of disruption (i.e. insertion sequence insertion vs non-sense or frameshift mutations).

 

These data are the first to indicate that the risk of colistin-resistance is a strain-specific trait that may differ by clonal group. These findings may have important implications for the treatment of carbapenem-resistant K. pneumoniae infections, and support the need for further large-scale studies to fully evaluate and compare strain-specific resistance risks.