Characterisation of mobile colistin resistance genes (mcr‑3 and mcr‑5) in river and storm water in regions of the Western Cape of South Africa
Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
BMC (part of Springer Nature)
Abstract
Background: Colistin is regarded as a last-resort antimicrobial against multi-drug resistant Gram-negative bacteria
(GNB), therefore the dissemination of colistin resistance in the environment is of great concern. Horizontal transfer of
mobile colistin resistance (mcr) genes to potential pathogens poses a serious problem. This study aimed to describe
the presence of colistin resistant GNB and mcr genes in river and storm water in regions of the Western Cape.
Methods: Water samples were collected from three rivers during May 2019 and January 2020 and two storm water
samples were collected in November 2019. Colistin resistant GNB were cultured on MacConkey agar containing colistin
and identified by MALDI-TOF. Colistin resistance was confirmed using broth microdilution (BMD). mcr-1-5 genes
were detected by PCR performed directly on the water samples and on the colistin resistant isolates. mcr functionality
was assessed by BMD after cloning the mcr genes into pET-48b(+) and expression in SHuffle T7 E. coli.
Results: mcr-5.1 and various mcr-3 gene variants were detected in the Plankenburg-, Eerste- and Berg rivers and in
storm water from Muizenberg, and only mcr-5.1 was detected in storm water from Fish Hoek. Colistin resistant GNB
were isolated from all of the water sources. Aeromonas spp. were the most common colistin resistant organisms
detected in the water sources; 25% (6/24) of colistin resistant Aeromonas spp. isolated from the Berg river contained
novel mcr-3 variants; mcr-3.33 (n = 1), mcr-3.34 (n = 1) mcr-3.35 (n = 1) mcr-3.36 (n = 2) and mcr-3.37 (n = 1), which
were confirmed to confer colistin resistance.
Conclusions: The mcr-5.1 and mcr-3 colistin resistance gene variants were present in widely dispersed water sources
in regions of the Western Cape. The mcr genes were only detected in water sampled downstream of and alongside
communities, suggesting that their presence is driven by human influence/contamination. This is the first documentation
of mcr-3 and mcr-5 gene variants in any setting in South Africa. Spill-over of these genes to communities could
result in horizontal gene transfer to pathogenic bacteria, exacerbating the challenge of controlling multidrug resistant
GNB infections.
Description
CITATION: Snyman, Y., et al. 2021. Characterisation of mobile colistin resistance genes (mcr‑3 and mcr‑5) in river and storm water in regions of the Western Cape of South Africa. Antimicrobial Resistance and Infection Control, 10:96, doi:10.1186/s13756-021-00963-2.
The original publication is available at https://aricjournal.biomedcentral.com
Publication of this article was funded by the Stellenbosch University Open Access Fund
The original publication is available at https://aricjournal.biomedcentral.com
Publication of this article was funded by the Stellenbosch University Open Access Fund
Keywords
River water, Storm water, Antimicrobial drugs, Colistin, Gram-negative bacteria, mcr genes, Pathogenic bacteria
Citation
Snyman, Y., et al. 2021. Characterisation of mobile colistin resistance genes (mcr‑3 and mcr‑5) in river and storm water in regions of the Western Cape of South Africa. Antimicrobial Resistance and Infection Control, 10:96, doi:10.1186/s13756-021-00963-2