摘要Vibrio parahaemolyticus is the main cause of foodborne gastroenteritis,which is widely distributed in shellfish and other seafood.Most V parahaemolyticus are nonpathogenic,and only a few types,such as serotype O3:K6,are pathogenic,which is also the most prevalent strain in Asia.However,the relationship between this serotype and pathogenicity has yet to be established.The waaf gene is located in the O antigen synthesis gene cluster.Thus,we constructed a waaf gene deletion mutant(i.e.,△waaf)of wild-type(WT)which isolated from shellfish serotype O3:K6 via chitin-mediated transformation technology.We then constructed the △waaf complementary strain(i.e.,C-△waaf)via the Escherichia coli S17 λpir strain by conjugation.The basic physiological characteristics,adhesion to Caco2 cells,and pathogenicity of the WT,△waaf,and C-△waaf strains were compared.Growth curves showed no remarkable differences between the WT and △waaf strains.However,the △waaf strain non-reactive to O3 antisera and other 12 O-group antisera of V parahaemolyticus.Moreover,the number of flagella and extracellular polysaccharides decreased,the adhesion decreased,and the pathogenicity weakened.These characteristics of the C-△waaf strain were similar to those of the WT strain.These results indicated that the waaf gene is vital to the serotype in V parahaemolyticus,and changes in O antigen could affect the pathogenicity of this bacterium.This study will be helpful to understand the pathogenic mechanism of V parahaemolyticus.