Although previous studies have analyzed bacterial diversity and community composition in marine ecosystems, some focused on the relationship between pathogenic bacteria and the composition of bacterial communities in sewage outfalls. The interactions between four pathogenic bacteria (E. coli, Enterococcus, Staphylococcus aureus, fecal coliforms) isolated from the sewage outfall and the bacterial diversity were investigated in the sea adjacent to the Xinghai sewage outlet, China to illustrate the influence of pathogenic bacteria on the bacterial community structure. Higher bacterial diversity was observed in the sewage outlet, and the abundance of pathogenic bacteria and bacterial diversity generally decreased with the increase in the distance from the sewage outlet. Bacterial community structure was mainly influenced by water temperature, conductivity, and dissolved oxygen in summer and winter, while pH, Oxidation-Reduction Potential and salinity were the main factors in autumn. The bacterial abundance had the most significant correlation with E. coli, followed by Enterococcus and fecal coliforms, and the least with Staphylococcus aureus. E. coli (-0.76 < r < 0.79) and Enterococcus (-0.88 < r < 0.77) had similar correlations to the same bacteria, in contrast to Staphylococcus aureus (-0.62 < r < 0.63). The above suggested that pathogenic bacteria may affect the bacterial community structure in the sea adjacent to the sewage outlet besides environmental factors.

Dalian Jinshitan beach was chosen to evaluate the impact of a typhoon on the bacterial community structure and water quality of a marine bathing beach. The concentration of enterococci was determined by the cultivation method. The bacterial community structure and abundance were analyzed using the 16S rDNA next-generation sequencing and qPCR methods. Results showed that the abundance of cultivable enterococci both in alongshore and offshore seawater increased, while it decreased in dry, wet and submerged sand. The water quality deteriorated immediately after the typhoon, and nearly recovered one month after the typhoon. The typhoon event also decreased the bacterial abundance and changed the bacterial community of the beach. Sphingomonadaceae and Rhodobacteraceae significantly increased in seawater and decreased in dry sand immediately after the typhoon. Human and other fecal taxa increased in water and sand. One month after the typhoon, the diversity and many dominant bacterial taxa nearly recovered in seawater and wet sand. Our work shows that the typhoon changed the bacterial dynamics, deteriorated the water quality and proved the transportation of bacterial taxa and input of fecal pollution between water and beach sand or land. Apart from the impact of the typhoon, the geographical location was another important factor in the changed bacterial community.