Importance of subunit vaccine antigen of major Fli C antigenic site of Salmonella Enteritidis II: A challenge trial

Abstract Salmonella enterica subsp. enterica serovar Enteritidis (SE) infection in chickens shows a mild pathogenicity except for young ages, compared with other animals, and laying hens sometimes produce SE-contaminated eggs leading to public health concerns. To reduce the problem, SE bacterin in poultry farms has been applied. We previously demonstrated that a subunit antigen, g.m. part polypeptide in SE-Fli C (SEp 9), could be a candidate subunit antigen of SE vaccine which may show less side effects in chickens. In this study, we used SEp 9 along with an adjuvant to inoculate chickens, then the chickens were orally challenged with SE, and suppression of the SE count in the cecum was investigated. Chickens inoculated with a commercial SE vaccine were prepared as positive controls (vaccine group), and those with physiological saline (control group) for comparison of the bacterial count after challenge. Employing two types of antibody-detection ELISA coated with either de-flagellated SE or SEp 9, specific antibody levels in blood and the intestine were determined. The bacterial count was significantly lower 1 and 3 weeks after challenge in the SEp 9 than in the control group. Specific antibody only against SEp 9 in blood but not the intestine of these birds in the SEp 9 group was detected. This study confirmed that SEp 9 antigen is a major effective antigen in SE inactivated vaccine, and it is suggested that only the subunit vaccine antigen SEp 9 is needed to effectively suppress colonization in the chicken intestine, without the need for other SE component antigens.