Asellus aquaticus: A Possible Reservoir for the Spread of Antimicrobial-Resistant Escherichia coli in the Environment
Creators: name: Odell, Amelia
Publisher: name: University of Lincoln
Year: 2023

description: Antimicrobials have saved millions of human lives, but antimicrobial resistance (AMR) has become a worldwide threat to human health, impairing our ability to treat bacterial infections. Although wildlife does not generally encounter AMR, they may become infected with AMR bacteria, and once they acquire AMR bacteria they may serve as a reservoir and vector of AMR. Thus, studying the prevalence of AMR in wildlife is important to maintaining public health. Extended-Spectrum ?-Lactamase (ESBL) producing Escherichia coli has been identified as a source of AMR in the environment and is associated with Waste Water Treatment Plant (WWTP) effluent. ESBL-producing organisms from WWTPs may be an important route for ESBL-producing organisms to enter the wider environment and pass through the food chain. Since 2015, another important AMR gene mcr-1 that causes resistance to colistin, one of the ‘last line of defence’ antibiotics has spread worldwide. To study the prevalence of AMR in the wider environment, this study examined the incidence of AMR E. coli from a watercourse (the Sincil Dike) that receives discharge from a WWTP. Specifically, temporal and spatial patterns in AMR prevalence were determined from i) water samples and ii) Asellus aquaticus(a freshwater invertebrate common to rivers and lakes). The geography of the site enabled a control watercourse (the River Witham) that did not receive WWTP effluent water and was sampled at the same time. Over a seven-month period, 200ml of water and ten Asellus aquaticus invertebrates were recovered from each location every month. The samples were taken from the WWTP effluent on the Sincil Dike and 1km up and downstream on both watercourses. The water samples and A. aquaticus samples were processed. CHROMagar ESBL agar was used to isolate and identify ESBL-E. coli. The presence of AMR genes was confirmed using the ‘BSAC’ method and PCR analysis to confirm the presence of ESBL and mcr-1 producing E. coli. Total viable counts (TVCs) from the water samples were highest from the WWTP effluent on the Sincil Dike. The TVC from A. aquaticus followed a similar pattern, with those sampled from the WWTP effluent being the higher. Over the sampling period, the TVCs of both water and invertebrate samples were influenced by the interaction between site and month. The CHROMagar ESBL agar was found to be 100% (n=234) accurate when confirmed with a PCR analysis of the AMR genes. Eighty-six percent (n=201) of the isolated ESBL-producing organisms were correctly identified as ESBL-E. coli using the ‘BSAC’ method. Fifty percent (n=117) of the ESBL-E. coli were also found to carry the mcr-1gene. In total, this study identified 234 isolates as ESBL-E. coli from the water and A. aquaticus samples. The mcr-1 gene and the blaTEM, blaSHV and blaCTX-M ESBL-genes were identified using plasmid DNA from the isolated organisms, it is not known if these genes are present on the same plasmids. The presence of these genes together points to the possible horizontal transfer of these genes within the bacterial population within the local environment.