Division of Medical Microbiology, Department of Pathology, Stellenbosch University, Cape Town, South Africa.
National Health Laboratory Service, Tygerberg Hospital, Cape Town, South Africa.
Antimicrob Resist Infect Control. 2021 Jun 29;10(1):96. doi: 10.1186/s13756-021-00963-2.
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.
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.
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.
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.
多黏菌素被视为对抗多重耐药革兰氏阴性菌（GNB）的最后一道抗菌药物，因此多黏菌素耐药性在环境中的传播引起了极大关注。移动多黏菌素耐药（mcr）基因向潜在病原体的水平转移构成了严重问题。本研究旨在描述西开普省各地区河流水和暴雨水体中存在的多黏菌素耐药 GNB 和 mcr 基因。
于 2019 年 5 月和 2020 年 1 月从三条河流以及 2019 年 11 月从两个暴雨水体中采集水样。在含有多黏菌素的麦康凯琼脂上培养多黏菌素耐药 GNB，并通过基质辅助激光解吸电离飞行时间质谱（MALDI-TOF）进行鉴定。使用肉汤微量稀释法（BMD）确认多黏菌素耐药性。通过直接在水样和多黏菌素耐药分离株上进行 PCR 检测 mcr-1-5 基因，并将 mcr 基因克隆到 pET-48b(+) 中后通过 BMD 评估 mcr 基因的功能。
在 Plankenburg 河、Eerste 河和 Berg 河以及 Muizenberg 的暴雨水体中检测到 mcr-5.1 和各种 mcr-3 基因变体，而在 Fish Hoek 的暴雨水体中仅检测到 mcr-5.1。从所有水源中均分离到多黏菌素耐药 GNB。在水源中最常见的多黏菌素耐药菌是气单胞菌属，从 Berg 河分离的 25%（6/24）多黏菌素耐药气单胞菌属含有新型 mcr-3 变体；mcr-3.33（n = 1）、mcr-3.34（n = 1）、mcr-3.35（n = 1）、mcr-3.36（n = 2）和 mcr-3.37（n = 1），这些变体均被证实可赋予多黏菌素耐药性。
mcr-5.1 和 mcr-3 多黏菌素耐药基因变体存在于西开普省广泛分散的水源中。mcr 基因仅在社区下游和周边采样的水样中检测到，这表明其存在是由人为影响/污染驱动的。这是南非任何环境中首次记录 mcr-3 和 mcr-5 基因变体。这些基因向社区的溢出可能导致水平基因转移到致病性细菌，从而加剧了控制多重耐药 GNB 感染的挑战。
