Discussion
Our investigation found outbreaks of diarrhea and death in piglets drinking mountain spring water. We isolated a novel hemolytic Gram-negative bacterium in the fecal samples and drinking water of piglets with diarrhea and named GDHYZ30. 16SrRNA analysis demonstrate that the bacteria is close to Chromobacterium haemolyticum . Then we designed the Koch postulates experiments to confirm that the GDHYZ30 strain is the causative agent of piglet diarrhea and death. Then the whole gene sequencing analysis of the GDHYZ30 strain was carried out. The phylogenetic tree based on 16SrRNA showed that the GDHYZ30 strain belongs to the same branch as Chromobacterium haemolyticum , but the homology is only 79%, indicating that this strain may belong to a new group, mainly causing diseases characterized by acute diarrhea and death. It has been reported that Chromobacterium haemolyticum has anti-bacterial properties, and we speculate that infection withChromobacterium haemolyticum, except of the direct intestinal damage, may cause changes in the intestinal flora, reducing beneficial bacteria and leading diarrhea consequently as well. (Zwe et al., 2021). At the same time, we found that infection with this novelChromobacterium haemolyticum can cause death, and intramuscular injection of the GDHYZ30 strain even can cause acute death of piglets. Meanwhile, the GDHYZ30 strain could be isolated from the blood samples and hearts of dead pigs, while the gavage group only caused diarrhea. These results suggest that bacteria can cause bacteremia leading to acute death, mainly through wound infection, and the results are similar to the way humans are infected with Chromobacterium haemolyticum .(Harmon, Mortensen, Robinette, & Powell, 2016; Miki & Okada, 2014). The bacteria have 390 virulence genes and 57 drug resistance genes, whether these genes are pathogenic still needs further research. Clinical trials and drug resistance analysis show that this novel Chromobacterium haemolyticum is a potential threat to humans and animals. The suitable conditions for the growth ofChromobacterium haemolyticum are near moist water sources, and the geographical location and climate of Guangdong Province are very suitable for the reproduction of Chromobacterium haemolyticum(Lima-Bittencourt, Costa, Barbosa, Chartone-Souza, & Nascimento, 2011; Priya et al., 2018). We also detected Chromobacterium haemolyticum in the drinking water of other pig farms with unexplained diarrhea, and after changing the water source, the piglet diarrhea was controlled. Therefore, checking the sanitation of water sources can prevent the occurrence of the disease.
Conflicts of interest
All authors declare that they have no conflicts of interest.
Acknowledgements
Funding: This study was supported by the National Key Research and Development Program of China (2018YFD0501102), the Key-rea Research and Development Program of Guangdong Province (2019B020211003).