Colistin resistant Acinetobacter baumannii in Cape Town, South Africa

A. baumannii isolates identified by Vitek® 2 AES™ as resistant were collected from Tygerberg Hospital referral microbiology laboratory from May 2016 to August 2017. Plasmid-mediated colistin resistance genes, mcr-1-5, were screened by PCR. In addition, chromosomal colistin resistance mechanisms were screened for by whole genome sequencing (WGS) on a selection of isolates. Strain typing was performed by rep-PCR and WGS MLST and a pairwise single nucleotide polymorphism (SNP) distance matrix was also performed on a selection of isolates. An increase in colistin resistant A. baumannii isolates in 2017 appears to be clonal expansion of an emerging colistin resistant strain within the hospital. This strain was not detected in 2016 or in isolates from other hospitals. Identical colistin susceptible strains were also isolated in the same hospital, suggesting relatively recent acquisition of the colistin resistance mechanism.