Resistance of Litopenaeus vannamei from Shanghai to Vibrio parahaemolyticus and detection and analysis of resistance genes

【Objective】In order to provide theoretical basis for scientific control of Vibrio parahaemolyticus disease in Litopenaeus vannamei and further reveal the antibiotics resistance mechanism of V. parahaemolyticus, the antibiotics resistance and the carrying status of related resistance genes were detected in V. parahaemolyticus isolated from L. vannamei in Shanghai, the correlation between resistance phenotype and resistance genes was also studied.【Method】The susceptibility of 21 strains of V. parahaemolyticus(isolated from L. vannamei in Shanghai) against 14 common antibiotics were detected by K-B disc diffusion test, and the minimum inhibitory concentration(MIC) and minimum bactericidal concentration(MBC) of more sensitive antibiotics were determined by double dilution method. The carrying statuses of blaTEM and blaCARB of β-lactam resistance genes, Sul II and Sul III of sulfanilamide resistance genes, strA and strB of aminoglycoside resistance genes, tet A of tetracycline resistance genes and inT1 of integrons of class I genes in V. parahaemolyticus were detected by PCR method.【Result】The 21 strains of V. parahaemolyticus showed multi-drug resistance to 14 antibiotics, which were one strain of resistance manifested to 6(4.76%), three strains of resistance manifested to 5(14.29%), five strains of resistance manifested to 4(23.81%), eight strains of resistance manifested to 3(38.10%) and four strains of resistance manifested to 2(19.05%). The dominant antibiotic resistance phenotypes were AMP/PG/SMX and PG/SMX. For the sensitivity rates of the tested antibiotics in the strains of V. parahaemolyticus, enrofloxacin was the most sensitive antibiotic(90.48%). MIC and MBC of enrofloxacin were 0.10-1.60μg/mL and 3.20-12.80μg/mL. PCR results of resistance genes showed that the detection rates of gene blaTEM, blaCARB, Sul II, Sul III, strB and inT1 were 23.81%, 71.43%, 33.33%, 19.05%, 9.52% and 23.81%, respectively. str A and tetA were not detected. A total of 11 drug-resistant genotypes were detected from 21 strains of V. parahaemolyticus from L. vannamei in Shanghai, the dominant genotypes including blaCARB(28.57%), blaCARB-blaTEM(14.29%), blaCARB-Sul II(14.29%) and Sul III-inT1(9.52%). Except str A and tetA, other resistance genes were correlated with their antibiotic resistance phenotypes, but the correlation was not significant(P>0.05).【Conclusion】The strains of V. parahaemolyticus isolated from L. vannamei in Shanghai showed different sensitivity levels to 14 antibiotics, enrofloxacin with the most sensibility. So, enrofloxacin can be considered as an alternative drug for the prevention and control of V. parahaemolyticus in L. vannamei in Shanghai. Besides, to solve the problem of multiple drug resistance of V. parahaemolyticus, detecting drug resistance genes and integrons in V. parahaemolyticus frequently and studying the trends are recognized as the effective strategies in V. parahaemolyticus prevention and control in L. vannamei.