Salmonella infection in calves: virulence proteins and its immunogenic properties

Seleim, R. S.*; Sahar, R. Mohamed; Novert, M. Hafez ; and Gobran, R. A.
Bacteriology Department, Animal Heahth Research Institute, Doki, Cairo, Egypt. *Corresponding author
SUMMARY
Faecal samples collected from calves suffering from diarrhoea revealed the isolation of Salmonella in 17.5% of the cases, while in the contact apparently healthy calves the incidence was 3.4%. Four salmonellaserovares were elucidated namely, S. typhimurium (7.3% and 1.7%), S. dublin (5.1% and 0.8%), S. enteritidis (2.9% and 0.8%) and S. anatum (2.2% and 0%) from diarrhoic and apparently healthy calves respectively. SDS-electrophoretic analysis of the outer membrane protein (OMP) revealed common antigen protein bands especially between S. dublin and S. enteritidis, due to the greater similarity in theirantigen structure. All serovars showed intense protein bands in the range from 20K to 45K. In the Western blot analysis, serum antibodies from calves infected with S. typhimurium (serogroup B) reacted with protein bands at the range of 17K, 24K, and 31K. The OMP of the two serovars S. dublin and S. enteritidis (both serogroup D1) reacted relatively similar in Western blot with the antiseracollected from calves infected with their corresponding serovars. Two protein bands were characteristic for S.dublin and S. enteritidis, 14.4K and 24K. Only one protein band, 24K from the blotted OMP of S. anatum (serogroup E1) reacted with serum from infected calves infected with that serovar. Using the heterologous serum in the Western blot analysis gave weaker results than the homologous serum.ELISA results detected the presence of serovar specific antibodies, S. typhimurium ELISA detected 10.9% and 4.3%, S. dublin ELISA detected 7.3% and 2.6%, S. enteritidis ELISA detected 5.1% and 1.7%, while S. anatum ELISA detected 2.9% and 0.9% of the serum samples collected from diarrhoic and apparently healthy calves respectively. It could be concluded that Salmonella OMP were majorimmunogenic antigens that could be used in ELSA or Western blot to detect and monitor Salmonella infection in calves.
INTRODUCTION
Salmonella infections in calves continue to be a major problem worldwide. Substantial economic losses were manifested through mortality and poor growth of infected animals as well as the hazard of transmitting food poisoning to humans. Many outbreaks of salmonellainfections has been reported world wide which encountered the most frequently isolated serovars as S. typhimurium, S. enteritidis, S. anatum S. newport, S. cerro, S. montevideo, S. agona and S. dublin which was considered the major host-adapted salmonella for cattle (Mitz et al. 1981, Konrad et al. 1994; Ritchie et al. 2001 and Veling et al. 2002).
The infection was always aggravated by poor hygienicconditions and inadequate nutrition and young calves were most susceptible to infection due to their immature immune responses, undeveloped microflora in their gastrointestinal echo-system and the permanent exposure to the source of infection from the environment and their dams. Calves suffering from acute clinical salmonellosis may shed 108-1010 Salmonella/gram faeces and animals recovering from theinfection may continue to be shedders of the organism for 2-12 weeks post infection. Shedding Salmonella by animals without clinical signs may be associated with chronic Salmonella infection (carrier), convalescence after acute infection or a recent starting colonization (Smith et al. 1989, Galland et al. 2000, Roy et al. 2001 and Radke et al. 2002).
Unlike the intermittent shedding ofSalmonella in the faeces, antibody levels do not fluctuate greatly on daily basis. Sero-conversion was used in many countries as a tool for Salmonella surveillance and control in cattle, pig and poultry industry at slaughter to identify infected flocks as a regulatory procedures for food safety and security program. Application of ELISA can provide information about the infection status of the animal and...