Phenotypic and Genotypic Characterization of a Highly VirulentStrain.

Abstract

is responsible for erysipelas infection in pigs. Outbreaks ofhave increased in several countries, including China, over the past two decades. Anstrain (ML101) was isolated and characterized from dead pig tissue sample collected from a farm experiencing an outbreak of, which was responsible for the deaths of 146 sows and 308 fattening pigs within a week. Spleen swelling, gastric and bladder mucosa bleeding, and submandibular lymph node swelling and bleeding were observed through necropsy. ML101 was identified as serotype 1a via molecular analysis and immunological assays. Studies in mice demonstrated that the minimal lethal dose per animal was less than 10 colony-forming units (CFU). Notably, the minimal lethal dose in piglets was also less than 10 CFU, which is lower than that of anystrain reported to date. The challenged piglets showed typical acute erysipelas symptoms, such as pyrexia, hemorrhage, depression, complete inappetence, reddening, and purpling skin on the buttock. Evidence of efficient horizontal transmission was observed, as healthy pigs were infected and died when cohoused with challenged piglets. Whole-genome sequencing revealed that ML101 contained a 77 kb genomic island (GI), carrying a Tntransposon and a multidrug resistance gene cluster (()-()-). A retrospective analysis ofisolates via PCR indicated that the GI has been widely distributed since 2010, when outbreaks were more frequently reported in China. This study demonstrated that the highly virulentis responsible for the erysipelas outbreak and indicates that relevant genes located within the transmissible genetic elements may play roles in virulence. Therefore, epidemiological monitoring needs to be emphasized to better prevent and control erysipelas in the swine industry, and live attenuated vaccines should be used with caution.