Colistin Resistance Mechanisms in Clinical Escherichia coli and Klebsiella spp. Isolates from the Western Cape of South Africa

Yolandi Snyman*, Andrew Christopher Whitelaw, Sandra Reuter, Motlatji Reratilwe Bonnie Maloba, Mae Newton-Foot

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Objectives: Colistin is a last-resort antibiotic for the treatment of carbapenem-resistant Gram-negative infections. Colistin resistance thus poses a threat to human health. Colistin resistance is most commonly encoded by mutations in chromosomal pmrA, pmrB, phoP, phoQ, ccrB, and mgrB genes, and the presence of plasmid-mediated mcr genes. This study describes colistin resistance mechanisms in clinical Enterobacterales isolates from the Western Cape, South Africa. Results: Escherichia coli (n = 22) and Klebsiella spp. (n = 7) isolates, from nine health care facilities, were confirmed to be colistin resistant during 2016 and 2017. mcr-1 was present in 55% (12/22) of E. coli and 71% (5/7) of Klebsiella spp. isolates. Colistin resistance mutations in pmrB were identified in 8/10 mcr-negative E. coli isolates using whole-genome sequencing, with pmrB Pro-94→Gln being the most frequent with presence in 4 isolates. One mcr-negative Klebsiella spp. isolate had a complete deletion of the mgrB and one contained an insertion sequence (IS1) in mgrB. Conclusion: A reduction in the proportion of colistin-resistant isolates harboring mcr-1 from 2016 to 2017 was observed. Colistin-resistant E. coli attributed by chromosomal mutations in pmrB in 2017 were mostly clonal related, which contrasts with the 2016 unrelated mcr-1-positive isolates. The diverse strains, hospitals, and resistance mechanisms may suggest that selective pressure is the main driver of colistin resistance.

Original languageEnglish
Pages (from-to)1249-1258
Number of pages10
JournalMicrobial Drug Resistance
Issue number9
Publication statusPublished - 1 Sept 2021
Externally publishedYes


  • Enterobacterales
  • South Africa
  • colistin resistance
  • mutations
  • whole genome sequencing


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