Flagella and curli fimbriae are important for the growth of Salmonella enterica serovars in hen eggs

1 Food Microbiology Collaborating Unit, Health Protection Agency, School of Clinical Veterinary Science, University of Bristol, Langford, Bristol BS40 5DT, UK 2 School of Biological and Chemical Sciences, University of Exeter, Exeter, Devon EX5 4PS, UK 3 Laboratory of Microbiology, Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania 19348-1692, USA 4 Department of Bacterial Diseases, Veterinary Laboratories Agency (Weybridge), New Haw, Addlestone, Surrey KT15 3NB, UK 5 Division of Farm Animal Science, School of Clinical Veterinary Science, University of Bristol, Langford, Bristol BS40 5DT, UK Correspondence T. A. Cogan tristan.cogan{at}bristol.ac.uk Salmonella enterica serovar Enteritidis is unable to multiply in the albumen of fresh eggs and must gain access to the yolk contents in order to multiply to a high level (>10 6 c.f.u. per ml egg contents). As human Salmonella infections resulting from the consumption of infected eggs more frequently involve serovar Enteritidis phage type (PT) 4 than other serovars or PTs, a number of isolates of various S. enterica serovars were examined for their ability to multiply to a high level in eggs over a period of 8 days storage at 20 °C. Their behaviour was compared to that of a range of defined fimbrial and flagella mutants of S . Enteritidis. Strains that did not express flagella were unable to multiply in eggs, and those deficient for curli fimbriae, including strains of S . Enteritidis PT6, displayed high-level growth in significantly fewer eggs than those able to express curli. Most S . Enteritidis strains multiplied to a high level in between 5 and 10 % of eggs during 8 days storage. One PT4 strain, though, showed high levels of growth in more than 25 % of eggs over this period, significantly higher than the other PTs or the two other isolates of PT4 tested. This ability may be important for the association of PT4 infection with the consumption of eggs. Abbreviations: LPF, long polar fimbriae; PT, phage type; PEF, plasmid-encoded fimbriae; TMB, tetramethylbenzidine