Studies of AmpC beta-lactamase gene diversity in aquatic systems

Abstract

An intensive literature review has revealed that there is a global lack of research on AmpC beta-lactamase antibiotic resistance genes in the aquatic environment. The possibility of the dissemination of AmpC genes within and among human settlements, and the consequent spreading and impact of antibiotic resistance due to their prevalence, are matters of grave concern as these genes pose potential threats not only to the environment, but to human health as well. Moreover, a dire implication of the prevalence of these genes in the environment and their exposure to selective pressures and unprecedented evolution may be that novel resistance mechanisms are introduced in clinical settings that may limit treatment options with beta-lactam antibiotics. This group of antibiotics is one of the most preferred bacterial treatment options in human, veterinary and agricultural settings and it is therefore imperative to manage resistance to any of these antibiotics. Therefore, the overarching aim of this study was to explore AmpC beta-lactamase gene intricacies in aquatic systems. To achieve this aim, various intersecting studies were conducted. The first assessed the prevalence and diversity of AmpC beta-lactamase genes in aquatic systems globally by reviewing to what extent research has been conducted on AmpC genes in aquatic environments. A second study determined the prevalence and genetic diversity of AmpC genes in South African rivers. The need for suitable quantification methods of AmpC genes prompted the third study that evaluated quantification methods of AmpC genes for environmental DNA samples. The final study determined which environmental parameters are associated with the prevalence of clinically relevant AmpC genes in aquatic environments. The systematic review determined that very few studies had explored AmpC genes in aquatic environments in the global context. By utilising experimental investigations, it was determined that clinically relevant AmpC genes are present in South African rivers that run either through densely or more sparsely human populated areas and that these genes are genetically diverse from gene variants found on sequence databases. The preferred method for the quantification of AmpC genes is the conventional quantitative PCR because it is forgiving regarding the unknown nature of environmental samples and is time efficient and financially viable when investigating numerous samples. It was also determined that there are limited significant associations between AmpC genes and environmental parameters and strong significant associations with population density. This suggests that AmpC genes are pre-selected and present in the aquatic environment due to human activities that cause pollution. Therefore, bacteria harbouring these genes are indicators of the presence of these genes in aquatic systems associated with faecal contamination. This study thus demonstrated the need for intensified research into AmpC beta-lactamase genes not only in South Africa, but globally for the sake of environmental and human health.