Investigating landscape-scale variables impacting human exposure to antibiotic resistant bacteria using a targeted metagenome approach

Research has shown that exposure to coastal waters containing antibiotic resistant bacteria (ARB) is associated with higher likelihood of gut colonisation by ARB. The aim was to identify landscape-scale processes contributing to the spread of ARB in Hong Kong's coastal waters and to estimate the scale of bathers' exposure to ARB. Twelve recreational water locations were sampled in 2017 for Escherichia coli. A targeted metagenomic approach was used to quantify the abundance and diversity of antibiotic resistance genes (ARGs) harboured by viable E. coli. Data on environmental variables related to ARB distribution in the environment were modelled to identify processes driving the abundance and diversity of ARG-bearing E. coli in coastal waters. These data were combined with data about Hong Kong residents' use of blue space to quantify human exposure to E. coli borne ARG. Several meteorological variables, like rainfall and temperature, were associated with E. coli-borne ARG profiles. Yet when rigorous statistical methods were applied, these relationships were not significant. Meropenem-resistant bacteria were also isolated from samples, most of which were taken from western beaches. Additionally, there was some evidence of elevated abundances of several ARGs, including bla_CTX-M, in western beaches. The average E. coli harboured 6.09 ARGs. Over 1.16 million exposure events occurred in 2017 that involved ingestion of E. coli harbouring at least one ARG. This study used robust methods to quantify and explain the abundance and diversity of ARB in Hong Kong's coastal waters. We detected elevated levels of several E. coli-borne ARGs and meropenem-resistant pathogens at western beaches, indicating an influence of the Pearl River on Hong Kong's water quality. Despite updates to wastewater treatment in Hong Kong, recreational use of natural surface waters remains a significant risk of exposure to ARB capable of human gut colonisation.