Antimicrobial spectrum, resistance gene detection and ERIC-PCR genotyping of Vibrio scophthalmi

From June to October of 2020, we had isolated 394 strains from diseased turbot (Scophthalmus maximus) in Liaoning Province, and identified them based on the 16S rRNA sequence. Then we randomly selected 18 Vibrio scophthalmi strains, which were further typed by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), so as to analyze the susceptibility to 8 antibiotics and the presence of drug-resistance genes. The results show that most of the isolates were Vibrio with 232 strains (58.88%), among which 117 strains (29.70%) were V. scophthalmi. The 18 strains identified by rpoD sequence alignment were not resistant to neomycin sulfate, flumequine and doxycycline hydrochloride, but resistant to other five antibiotics with different ratios. The multiple drug resistance rate was 66.7%. Five drug resistance genes in the 18 strains of V. scophthalmi were detected (Amide alcohol resistance genes floR of 61.11% and cmlA of 66.67%, sulfonamide resistance gene sul2 of 55.56%, quinolone resistance genes qnrA of 50% and qnrS of 5.56%). No aminoglycosides or tetracycline resistant genes were detected. The coincidence rate of amide alcohol resistance genes and drug resistance phenotype was 88.89%, indicating a certain correlation between them. Sulfonamide resistance genes had a coincidence rate of 50% with the resistance phenotype, and quinolones resistance genes had the lowest coincidence rate of 33.33%. Finally, we clustered the 18 strains into four types by using ERIC-PCR fingerprinting. Type I (44.44%) and Type III (44.44%) were the main clusters. We observed apparent absence of correlation between ERIC-PCR fingerprinting and the resistance phenotype or resistance genes. Thus, it is conluded that doxycycline hydrochloride can be the first choice for the control of V. scophthalmi in Liaoning aquaculture farms.