Clonal expansion of colistin-resistant Acinetobacter baumannii isolates in Cape Town, South Africa

Snyman, Yolandi ; Whitelaw, Andrew Christopher ; Reuter, Sandra ; Dramowski, Angela ; Maloba, Motlatji Reratilwe Bonnie ; Newton-Foot, Mae (2020-02-01)

CITATION: Snyman, Y. et al. 2020. Clonal expansion of colistin-resistant Acinetobacter baumannii isolates in Cape Town, South Africa. International journal of infectious diseases. International Society for Infectious Diseases, 91:94–100. doi:10.1016/j.ijid.2019.11.021

The original publication is available at https://www.journals.elsevier.com/international-journal-of-infectious-diseases

Article

Objectives: To describe colistin-resistant Acinetobacter baumannii isolates in Cape Town, South Africa. Methods: A. baumannii isolates identified on Vitek 2 Advanced Expert System were collected from Tygerberg Hospital referral laboratory between 2016 and 2017. Colistin resistance was confirmed using broth microdilution and SensiTest. mcr-1-5 were detected using PCR and strain typing was performed by rep-PCR. Whole genome sequencing (WGS) was performed on a subset of isolates to identify chromosomal colistin resistance mechanisms and strain diversity using multilocus sequence typing (MLST) and pairwise single nucleotide polymorphism analyses. Results: Twenty-six colistin-resistant and six colistin-susceptible A. baumannii were collected separately based on Vitek susceptibility; 20/26 (77%) were confirmed colistin-resistant by broth microdilution. Four colistin-resistant isolates were isolated in 2016 and 16 in 2017, from five healthcare facilities. Thirteen colistin-resistant isolates and eight colistin-susceptible isolates were identical by rep-PCR and MLST (ST1), all from patients admitted to a tertiary hospital during 2017. The remaining colistin-resistant isolates were unrelated. Conclusions: An increase in colistin-resistant A. baumannii isolates from a tertiary hospital in 2017 appears to be clonal expansion of an emerging colistin-resistant strain. This strain was not detected in 2016 or from other hospitals. Identical colistin-susceptible isolates were also isolated, suggesting relatively recent acquisition of colistin resistance.

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