The contribution of SEF14, SEF17, SEF21 and flagella to the pathogenesis of Salmonella enteritidis in poultry

Salmonella enteritidis continues to be a major cause of foodboume infections in the United Kingdom, the rest of Europe, and the USA with poultry implicated as a major source. To understand the virulence mechanisms of bacterial pathogens it is necessary to study directly host-bacterial interactions. For E. coli it is considered that adherence to enterocytes is a prerequisite to infection and the adhesive function of certain fimbriae have been described (Parry & Rooke, 1985). However, for Salmonella spp.the role of surface appendages is poorly understood. S. enteritidis express flagella and several tightly regulated fimbriae including SEF14 and SEF21 (type 1) that are morphologically and antigenically distinct. In addition, Collinson et al. (1991) demonstrated elaboration of aggregative SEF17 fimbriae by S. enteritidis 27655R, although conditions neccesary for expression of this surface appendage, other than strain 27655R, were unknown. In this study specific immunological reagents were raised to SEF17 and used to investigate the expression of SEF17 fimbriae by cultured strains of S. enteritidis. Elaboration of SEF17 was dependant upon temperature and media with optimal expression at 18°C on CFA agar. However, two wild type strains produced SEF17 when also grown at 30°C to 42°C. In addition, fine fimbriae produced by a strain of S. typhimurium and E. coli were specifically and strongly labelled by SEF17 monoclonal and polyclonal antibodies, indicating considerable antigenic conservation. A panel of mutants prepared in three strains of S. enteritidis defective for the elaboration of fimbrial types SEF14, SEF17, SEF21 and flagella were utilised to determine the role of these surface appendages in association with and invasion of cultured epithelial cells. In all assays, the naturally occuring regulatory defective strain 27655R associated to tissue culture cells significantly greater than LA5 and S1400. Compared with wild type progenitor strains, SEF14 mutants had no effect on association and invasion, whereas for both association and invasion, SEF17, SEF21 and aflagellate mutants showed significant reductions. Isogenic mutants prepared in a chicken isolate, S. enteritidis strain LA5, were used to study the contribution of these organelles in the colonisation, invasion, persistence and lateral transfer in young chicks. The caecum, liver and spleen were colonised within 24 hours following oral inoculation of day old chicks with 105 wild type S. enteritidis. SEF17, SEF21 and flagella contributed to a delay in colonisation of the spleen as did SEF21 and flagella mutants in the liver. Lower numbers of bacteria were recovered from the caecum with mutants deficient for SEF21 elaboration. LA5 and EAV40 (14', 17', 21', fla ) persisted for six weeks in the caecum and to a lesser extent the liver and spleen of birds. In addition, sentinel birds were colonised by LA5 or EAV40 directly from the environment within two days, although, a slight delay was observed with the multiple mutant. Overall, data from this study suggests that SEF17, SEF21 and flagella, but not SEF14, play a role in the early stages of colonisation and invasion of young chicks by S. enteritidis, but are unnecessary for S. enteritidis to persist for up to six weeks or colonise birds from their immediate environment.