Abstract
Riemerella anatipestifer causes serious contagious disease in ducks, geese, and other fowl. However, as a harmful pathogen causing significant economic losses in the poultry industry, R. anatipestifer is still poorly understood for its pathogenesis mechanisms. In a previous study, we developed an indirect ELISA method for detecting R. anatipestifer infection using B739_0832 protein, a putative outer membrane protein H (OmpH) that is conserved among different serotypes of R. anatipestifer. Although OmpH in some pathogenic bacteria, such as Pasteurella, has been reported as a virulence factor, it is still not clear whether B739_0832 protein contributes to the virulence of R. anatipestifer. In this study, we confirmed that B739_0832 protein in R. anatipestifer localizes to the outer membrane. We constructed a B739_0832 deletion mutant strain (ΔB739_0832) and assayed various effects from the deletion of B739_0832. ΔB739_0832 strain had a similar growth rate to wild-type R. anatipestifer CH-1. However, the survival rate of ducklings in 10 days after infection from ΔB739_0832 strain was 50%, whereas no ducklings survived from wild-type R. anatipestifer infection. Furthermore, the median lethal dose (LD50) of the ΔB739_0832 strain was approximately 150 times higher than that of the wild-type strain. Pathology examinations on infected ducklings found that, at 36 h after infection, bacterial loads in blood, liver, and brain tissues from ΔB739_0832-infected ducklings were considerably lower than those from wild-type infected ducklings. These results demonstrate that the B739_0832 protein contributes to the virulence of R. anatipestifer CH-1.
Highlights
Riemerella anatipestifer is a Gram-negative, rod-shaped bacterium in the Flavobacteriaceae family, Riemerella genus (Segers et al, 1993)
To further evaluate the influence of B739_0832 on systemic infection in vivo, bacterial loads in blood, liver, spleen, and brain from ducks infected by wild type, B739_0832, or C B739_0832 were quantified
The difference developed at 36 h, earlier than in spleen, which did not show significant difference until 48 h, whereas, in liver, the bacterial loads were different since 12 h post-infection, and the difference grew more significant at 48 h (Figure 5C)
Summary
Riemerella anatipestifer is a Gram-negative, rod-shaped bacterium in the Flavobacteriaceae family, Riemerella genus (Segers et al, 1993). Riemerella anatipestifer is one of the most serious bacterial threats harming mostly the duck industry, but R. anatipestifer infection has been reported in other waterfowl worldwide, causing heavy economic losses (Wang et al, 2010; Hu et al, 2012). Riemerella anatipestifer infection has high mortality and morbidity rate in young ducklings, but may be present in adult ducks causing only subclinical or even asymptomatic diseases (Chang et al, 2019), making it difficult to detect and eradicate. There is no cross-protection between different serotypes of R. anatipestifer developed from infection (Kang et al, 2018). With the diverse serotype variations, vaccines developed against R. anatipestifer have been shown to have low cross-protection against different serotypes (Chu et al, 2015). To safely and effectively control and prevent diseases caused by R. anatipestifer, new strategies for developing vaccines with cross-protection against different serotypes are needed
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