Phylogenetic relationships and antibiotic resistance of Vibrio parahaemolyticus isolates related to acute hepatopancreatic necrosis disease in Korea

In this study, we performed genotype analysis based on multi-locus sequence typing (MLST) and antibiotic resistance of 27 pirAB-harboring Vibrio parahaemolyticus (Vp AHPND) isolates recovered from white leg shrimp (Penaeus vannamei) from acute hepatopancreatic necrosis disease (AHPND) affected farms (in 2016, n = 22) and retail markets (in 2016, n = 5) of Korea. Most Vp AHPND isolates were resistant to colistin, ampicillin, and streptomycin but susceptible to other antibiotics. The comparison of their antibiotic resistance to that of non-Vp AHPND isolates revealed a significantly higher resistance of Vp AHPND isolates to streptomycin. No differences, however, were observed in the minimal inhibitory concentration median (MIC50), 90th percentile (MIC90), and average multiple antibiotic resistance (MAR) index between the two groups. In MLST analysis, sequence types could not be defined for 19 isolates owing to the failure of recA gene sequencing. Seven new STs were found in five and two isolates from retail markets and AHPND affected farms, respectively. Based on the MLST-based phylogenetic tree, all isolates were divided into eight clades; 22 isolates from AHPND affected farms were grouped into three clades, and five isolates from retail markets formed singleton clades. These data suggest that most AHPND outbreaks in Korea may be related to Vp AHPND isolates originating from a common clone through the acquisition of pirAB. Further, the detection of Vp AHPND from retail shrimp samples suggests that the pathogen may be widely distributed in shrimp aquaculture and/or the environment of Korea.