Relating the prevalence of plasmid-mediated AmpC beta-lactamase genes to aquatic environmental factors

It is important that environmental parameters that may affect the prevalence of AmpC beta-lactamase genes are investigated to devise frameworks for their surveillance, management and prevention. The aim of this study was thus to determine which environmental parameters are associated with the prevalence of clinically relevant AmpC beta-lactamase genes in aquatic systems. River water was sampled from seven sites in the Crocodile West River, South Africa. Physical-chemical parameters, metal levels and beta-lactam levels were measured. Environmental DNA was extracted from the water samples and six AmpC beta-lactamase gene groups (ACC, ACT/MIR, BIL/LAT/CMY, DHA, FOX, MOX/CMY) were quantified using quantitative PCR. Additionally, 16S rRNA gene metabarcoding analyses were performed on eDNA for each site and metabolic pathways were predicted using PICRUST2. Network analysis was performed to establish co-occurrences of AmpC genes with environmental factors. Quantification results indicated that AmpC gene copy numbers were significantly high (Kruskal Wallis H Test, p < 0.05) at Sites 1–3 of the Crocodile West River. In contrast, no significant changes regarding environmental factors were observed across the seven sites. Results of network analysis indicated that the AmpC gene groups had limited associations with all the environmental parameters, except for some key bacterial families, specifically Pseudomonadaceae, Aeromonadaceae and Enterobacteriaceae. A significant positive correlation between population density and AmpC genes suggested that in more densely populated areas more faecal pollution will be prevalent which is associated with high AmpC gene levels. Areas such as these are also likely to be linked with more antibiotic use which supports the notion that pre-selection of AmpC genes occurs before entering the aquatic environment. Moreover, it was demonstrated that prevalent selectors of AmpC genes do not ensure that continuous selection occurs in an aquatic environment. This information could be vital in future detection and management of AmpC genes in aquatic systems.