Clinical and biological properties
Our investigation found severe piglet diarrhea in one farm. The morbidity rate of piglets was 30.65% (149/486), and the mortality rate was 35.57% (53/149). To figure out the agents of diarrhea in piglets, we collected fecal samples from piglets with diarrhea and tested a variety of diarrhea-causing viruses including Porcine epidemic diarrhea virus; Porcine deltacoronavirus; Transmissible Gastroenteritis Virus; swine acute diarrhoea syndrome coronavirus; porcine rotavirus; Porcine circovirus type 3 and Porcine Circovirus-like Viruses by PCR methods, all the above pathogens could not be detected. Excitingly, a β-hemolysis bacterium was isolated (Fig.1A), which were Gram-stained negative, rod-shaped bacterium (Fig.1B). The strain was purified by colonization, and named as GDHYZ30 strain. Subsequently, Koch postulates experiments were conducted to verify the pathogenicity of the GDHYZ30 isolate. Nine 30-day-old healthy piglets were randomly divided into three groups. 2ml of 3.5x10^9CFU bacteria were administered orally or intramuscularly injected respectively, and 2ml of PBS was administered orally to the control group. At the second day, we found that all three piglets in the gavage group developed diarrhea (Fig.1C). One piglet in the intramuscular injection group had diarrhea and two piglets died. Piglets in the control group were asymptomatic. Piglets with diarrhea had thin intestinal walls and flatulence (Fig.1D). The GDHYZ30 strain could be isolated from the blood and heart of the dead piglets, but not from the piglets administered orally group. The above results indicated that the GDHYZ30 strain was the pathogen causing piglet diarrhea and acute death.