Prevalence of plasmid genetic elements among ESBL-producing E. coli isolated from a UK river and the effects of waste water effluent release
Creators: name: Dinatale, Adam
Publisher: name: University of Lincoln
Year: 2023
Subjects: C150 - Environmental biology
C510 - Applied microbiology

description: The global antibiotic resistance crisis is a growing issue which poses a significant threat to human and animal health, and will limit the effectiveness of infection treatment in clinical settings. Traditionally research efforts have concentrated on discovering novel antibiotics, however an alternative approach is being utilised which focuses on the control and removal of antibiotic resistance from the environment. A major source of environmental antibiotic resistance originates from the release of treated waste water effluent (WWE) from local waste water treatment plants (WWTP) into natural aquatic environments, such as canals and rivers. Study has shown released WWE contains high numbers of antibiotic resistant bacteria and residual active antibiotics. In particular members of the Enterobacteriaceae family expressing extended spectrum beta-lactamases (ESBLs), such as the highly prevalent CTX-M group 1 genes, have been commonly identified in WWE and have been shown to be more prevalent in natural aquatic environments following the addition of WWE. These ESBL genes are commonly plasmid borne, and their prevalence has been attributed to their ability to be rapidly disseminated by horizontal gene transfer. Once spread through the bacterial population, antibiotic resistance plasmids are maintained by the selective pressure of high levels of antibiotics, introduced to the environment by WWE. This study aimed to identify the effect of WWE addition on the ESBL expressing Escherichia coli (ESBLEC) population of natural aquatic environments, and the genetic elements found on plasmids extracted from ESBLEC isolates. ESBLEC were isolated from the Sincil Dike, Lincoln, UK upstream, at the point of and downstream of WWE release. Plasmid DNA was then extracted from these isolates and the genetic elements they contained identified by PCR, CTX-M group 1, 3 addiction systems (Hok-Sok, PemK and ccdAB) and 3 incompatibility groups (IncF, IncN and IncP) were detected. This data was arranged into unique plasmid genotypes which were used to determine the effect of WWE addition on the individual genetic elements identified, and on the ESBLEC plasmid population as a whole. It was found that the number of ESBLEC isolated increased at sample sites that had received WWE and was attributed to the influx of ESBLEC producing organisms previously identified in WWE. Further genetic analysis revealed that the increase in the number of ESBLEC was accompanied by a shift from a few dominant plasmid types to a larger number of genetically diverse plasmids. This diversification event appeared to favour IncF plasmids containing alternate ESBL genes and multiple addiction systems, which allowed their persistence downstream while competing with naturally occurring genotypes. Overall it is clear that the addition of WWE to natural aquatic environments has a measurable impact on the number of ESBLEC and the plasmid genotype they contain. This may have a significant effect on the transfer and maintenance of antibiotic resistance in the environment. A larger study which detects a wider range of plasmid genetic elements across a larger number of sample sites would allow for a deeper insight into the effects of WWE release on plasmid containing ESBLEC in the environment.