Antibiotic resistance genes might serve as new indicators for wastewater contamination of coastal waters: Spatial distribution and source apportionment of antibiotic resistance genes in a coastal bay

Rare information on using antibiotic resistance genes (ARGs) as new indicators for the wastewater contamination in coastal environment is available. This study investigated the distribution and sources of ARGs in a coastal bay influenced by anthropogenic activities including intensive wastewater discharge, which demonstrated that ARGs could be essential indicators for the wastewater contamination in coastal waters. Ten ARG subtypes encoding resistance to sulfonamides (sul1 and sul2), tetracyclines (tetB, tetG and tetX), quinolones (qnrA, qnrB and qnrS) and macrolides (ermF and ermT) were detected with high frequencies. The absolute abundances of ARGs in different functional zones of Sishili Bay differed greatly in the range of 100–108 copies/mL. The total abundances of ARGs in the zones influenced by wastewater treatment plants (WWTPs) and sewage polluted rivers were relatively higher with the maximum up to 6.1 × 106 copies/mL and 6.2 × 107 copies/mL, respectively. The TN, nitrite, and silicate had extremely significantly positive correlations (p < 0.01) with the abundances of all target ARGs, as well as ammonium and TOC had significantly positive correlations with the target ARGs. A total of 402 pairs of strong and significant correlations between bacteria and ARGs were identified in samples from the zones influenced by wastewater pollution sources (rivers and WWTPs), while only 232 pairs of correlations were identified in other samples. It indicated the occurrence and prevalence of potential multi-antibiotic resistant bacteria in coastal waters contaminated by wastewater. These findings revealed that the occurrence and distribution of ARGs in the coastal bay were mainly influenced by the wastewater discharge. ARGs might serve as new indicators for the influence of wastewater discharge on coastal water qualities, since the wastewater discharge has critical influences on ARGs pollution in coastal waters.