Characterisation of mcr-4.3 in a colistin-resistant Acinetobacter nosocomialis clinical isolate from Cape Town, South Africa

Colistin resistance in Acinetobacter spp. is increasing, resulting potentially untreatable nosocomial infections. Plasmid-mediated colistin of particular concern due to its low fitness cost and potential transferability other bacterial strains species. This study investigated the mechanism a clinical nosocomialis isolate from Cape Town, South Africa. A colistin-resistant A. was identified blood culture 2017. PCR Illumina whole-genome sequencing (WGS) were performed identify genes mutations conferring colistin. Plasmid on an Oxford Nanopore platform. mcr functionality assessed by broth microdilution after cloning gene into pET-48b(+) expressing it SHuffle® T7 Escherichia coli curing plasmid using 62.5 mg/L acridine orange. The minimum inhibitory concentration (MIC) 16 mg/L. mcr-4.3 detected WGS. No previously described found 24 024-bp RepB (pCAC13a). Functionality studies showed that recombinant did not confer E. coli. However, pCAC13a restored susceptibility nosocomialis. We describe first detection plasmid-mediated encoding Recombinant expression coli, suggesting may be plasmid-dependent or species-specific.