A new emerging serotype of Vibrio parahaemolyticus in China is rapidly becoming the main epidemic strain.

Abstract

OBJECTIVES\nDuring surveillance, we found a new type of Vibrio parahaemolyticus that agglutinated with O4 serum but not with K serum, and the recA gene was affected by a large insertion. We named this strain O4:KUT-recAin .\n\n\nMETHODS\nThe clinical data and stool specimens were collected from acute diarrheal patients in coastal hospitals of China. V. parahaemolyticus was isolated using selective media and identified by MALDI-TOF Microbial Mass Spectrometer. By serum agglutination tests and whole-genome sequencing, we identified a new serotype of V. parahaemolyticus strain. By using a rabbit diarrheal model, we confirmed the pathogenicity of this strain.\n\n\nRESULTS\nO4:KUT-recAin strain possessed a new type of K antigen and a 25 043 bp large fragment encoding 20 proteins inserted in housekeeping gene recA. Retrospective analysis found that only one O4:KUT-recAin strain was detected in 563 V. parahaemolyticus strains in 2014; then, the proportion increased rapidly and reached 17.8% (105/590) in 2016 and 31.1% (224/721) in 2017, making O4:KUT-recAin the second dominant serotype following O3:K6. O4:KUT-recAin strains (100%, 14/14) exhibited increased acid resistance and could reproduce in medium at pH= 4.9, while 92.9% (13/14) of the O3:K6 strains could not grow at this pH. O4:KUT-recAin could cause diarrhea and small intestinal tissue lesions in infant rabbits, but its diarrheal (93.1%, 27/29) and mortality (78.6%, 22/28) rates were slightly lower than those of O3:K6 (100% 16/16, 100% 16/16). Based on diarrhea patients, most clinical symptoms and laboratory results were no significant difference in the two groups, except media age, hemoglobin and the red blood cell in the stool.\n\n\nCONCLUSIONS\nO4:KUT-recAin had enhanced acid resistance, was capable of causing infectious diarrhea in both rabbits and humans, and has become widespread during a short period of time in China.