Contamination status, virulence gene distribution and drug resistance spectrum of Vibrio alginolyticus in seawater and seafood in Dapeng new district of Shenzhen, Guangdong, 2021−2022

Objective To investigate the contamination status of Vibrio alginolyticus in seawater and seafood in Dapeng new district of Shenzhen, Guangdong province, analyze the distribution of virulence genes and drug resistance spectrum of V. alginolyticus in the environment and provide data support the control of infections caused by V. alginolyticus.

Methods A study was conducted in the Dapeng between January 2021 and December 2022, in which samples of inshore seawater and commercial seafood collected every 3 months were used. V. alginolyticus was isolated and a broth dilution test was used to detect the susceptibilities of the isolates to 17 antibiotics. Polymerase chain reaction was used to amplify V. alginolyticus virulence-related genes including tdh, trh, tlh, toxR, fur, collagenase, toxS, ureR, flaA, ompW, aspA, and the products were analyzed by 1% agarose gel electrophoresis.

Results A total of 304 samples of seawater were collected, in which 103 were tested positive for V. alginolyticus, the detection rate was 33.88%. There were significant differences in the detection rate of V. alginolyticus in seawater among different seasons (χ²=10.090, P<0.05), with higher positive rates in the 1st and 4th quarters than in the 2nd and 3rd quarters. A total of 139 samples of seafood were collected, in which 108 were tested positive for V. alginolyticus, the detection rate was 77.70%. A total of 334 strains of V. alginolyticus were isolated from the seawater and seafood samples. The V. alginolyticus isolates showed high levels of resistance to ampicillin and colistin, with resistance rates of 85.63% and 45.94%, respectively. The 11 virulence-related genes were detected with different proportions.

Conclusions V. alginolyticus contamination, both in seawater and seafood, was a serious public health problem Dapeng new district. These strains carried complex and diverse virulence-related genes and showed multi-drug resistance. Long-term surveillance for V. alginolyticus in environment, including genotyping, detections of virulence genes and drug resistance and evolutionary analysis, is necessary to provide data support for further research of the evolutionary pattern of V. alginolyticus and the development of prevention and control strategies.