The potential risk of antibiotic resistance of Streptococcus iniae in sturgeon cultivation in Sichuan, China

Sichuan, located in the upper reaches of the Yangtze River, is the gathering place of many rivers and plays an important role in sturgeon aquaculture and wild sturgeon protection in China, where it suffered the severe influence of Streptococcus iniae infection in sturgeon. However, the annual thousands of tons of antibiotic usage in Sichuan may accumulate in water and cause obstacles to the prevention of S. iniae infection. In contrast, the regional antibiotic resistance characteristics have been rarely unknown. Seventeen S. iniae strains were collected from the major sturgeon culture areas in Sichuan, and the genotyping and the distribution of antibiotic resistance profiles (ARPs) and genes (ARGs) of S. iniae were established in this study. The results showed that the isolates could be divided into four subtypes by pulsed-field gel electrophoresis analysis. Besides, most isolates showed multiple resistance to the antibiotic such as amikacin, neomycin, enrofloxacin, lincomycin, and sulfamethoxazole. Also, sturgeon-derived S. iniae has a relatively low similarity with other fish-derived S. iniae in the world but high similarity with three animal-derived pathogens from Sichuan in previous studies. Moreover, a total of 37 ARGs were detected positively based on 95 ARGs detection, in which aac(6')-Ib(aka aacA4)-01, aac(6')-Ib(aka aacA4)-02, aadA1, floR, blaTEM, sulA/folP-03, and tetA-02 were most prevalent. Our study indicated that the ARGs of sturgeon-derived S. iniae were significantly enhanced compared with the ATCC29178 strains and have a risk of accessing more ARGs from other bacteria in water in Sichuan. This study claimed that sturgeon has a potential risk in the prevention and control of Streptococcosis in Sichuan, the upper reaches of Yangtze River, based on the antibiotic resistance analysis of S. iniae, and it may also increase the risk of highly resistant S. iniae transmission into the middle and lower reaches.