Biofilm-Formation-Related Genes csgD and bcsA Promote the Vertical Transmission of Salmonella Enteritidis in Chicken

The contamination of Salmonella Enteritidis in eggs and chicken meat via vertical transmission has become a worldwide public health concern. Biofilm formation by S. Enteritidis further enhances its antibacterial resistance. However, whether genes related to biofilm formation affect the level of vertical transmission is still unclear. Here, S. Enteritidis mutants Delta csgD, Delta csgA, Delta bcsA, and Delta adrA were constructed from wild type strain C50041 (WT), and their biofilm-forming ability was determined by Crystal violet staining assay. Then the median lethal dose (LD50) assay was performed to determine the effects of the selected genes on virulence. The bacterial load in eggs produced by infected laying hens via the intraperitoneal pathway or crop gavage was determined for evaluation of the vertical transmission. Crystal violet staining assay revealed that S. Enteritidis mutants Delta csgD, Delta csgA, and Delta bcsA, but not Delta adrA, impaired biofilm formation compared with WT strain. Furthermore, the LD50 in SPF chickens showed that both the Delta csgD and Delta bcsA mutants were less virulent compared with WT strain. Among the intraperitoneally infected laying hens, the WT strain-infected group had the highest percentage of bacteria-positive eggs (24.7%), followed by the Delta adrA group (16%), Delta csgA group (9.9%), Delta bcsA group (4.5%), and Delta csgD group (2.1%). Similarly, among the crop gavage chickens, the WT strain group also had the highest infection percentage in eggs (10.4%), followed by the Delta csgA group (8.5%), Delta adrA group (7.5%), Delta bcsA group (1.9%), and Delta csgD group (1.0%). Our results indicate that the genes csgD and bcsA help vertical transmission of S. Enteritidis in chickens.

Automated summary

The research shows that there is a correlation between the biofilm formation of Salmonella Enteritidis and its level of vertical transmission in chickens. The genes csgD and bcsA play a significant role in facilitating the vertical transmission of Salmonella Enteritidis in chickens.