Spatial and temporal analysis of the seasonal dynamics of antibiotic resistance gene occurrence in recreational marine water

People who engage in water sports in recreational marine water may be at high risk of exposure to hazardous antibiotic-resistant bacteria (ARB). However, information on the contribution of specific sources to ARB contamination in recreational marine water is still lacking. Here, we carried out monthly analyses of antibiotic resistance genes (ARGs), pathogenic bacteria and 16S rRNA sequencing data at the First Bathing Beach in Qingdao. The sampling sites were divided into four areas: swimming area, intermediate area, polluted area, and sewage outlet. Correlations between ARGs and bacterial communities among sampling sites were explored by spatial and temporal analysis. We found that all of 21 important ARG types were detected in the swimming area, with aadA (1.3 x 106 & PLUSMN; 2.7 x 106 genomic copies/L) and sul2 (4.3 x 105 & PLUSMN; 5.9 x 105 genomic copies/L) at the highest concentration. Most ARGs were detected at highest frequency and concentration in the sewage outlet and decreased from there to the swimming area. ARG correlation between these two areas was positive only in the cold season, suggesting that sewage was the main source of ARG pollution in the swimming area during that period. The ARGs ermA(1) and vanA were detected at highest frequency and concentration in the swimming area and were significantly correlated with the intestinal pathogen Enterococcus, which was more abundant here than in the surrounding areas during the warm season. Co occurrence analysis of bacterial genera and ARGs showed that six genera were commonly correlated with ARGs in all sampling areas in the cold season, while none were found in the warm season. Our findings indicate that ARG pollution in the swimming area was also driven by sources other than sewage, especially in the warm season, which is the peak tourist season in Qingdao. These results provide a valuable basis for the implementation of effective strategies to control ARG risks in recreational waters.