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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 6C. 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. INTRODUCTIONSalmonella infection resulting from the consumption of contaminated eggs is a major public health problem in Europe and the USA and an emerging one in the Far East (Poppe, 1999). Salmonella enterica subspecies enterica serovar Enteritidis is responsible for the majority of eggassociated infections, and appears to possess factors that enable it to persist in the reproductive tissue of the hen so that it can contaminate the contents of intact eggs (Okamura et al., 2001a, b). Other serovars of S. enterica, such as Gallinarum and Pullorum, have in the past been widespread in laying flocks (Shivaprasad, 2000), without a concomitant high level of human infection.Salmonella enterica has the potential to elaborate numerous cell surface structures, including type 1 (SEF21), thin aggregative or curli (SEF17), SEF14, long polar (LPF) and plasmid-encoded (PEF) fimbriae, and flagella. Many of these have been shown to be important in the process of infection of the hen and in the colonization of the reproductive tissues. SEF14 fimbriae, which are only present in a few group D serovars (Turcotte & Woodward, 1993), mediate adherence to reproductive tissues (Ogunniyi et al., 1997) and may have a role in organ invasion and persistence (Rajashekara et al., 2000). There is some evidence that flagella are important in the subsequent invasion of internal tissues . Type 1 and curli fimbriae in Escherichia coli, analogous to SEF21 and SEF17 of S. Enteritidis, are associated with initial persistence in the avian gastrointestinal tract (La Ragione et al., 2000). There is little current evidence for a role for PEF and LPF in virulence or persistence in the chick model, or in laying hens. The role of any of these in the growth of Salmonella within the egg is not yet known. Salmonel...

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Sections of kidney, trachea, ileum, colon, rectum and rumen were removed at post mortem from a neonatal calf and, with the exception of the rumen, primary cell lines were established for each of the cell types. The adherence of enterohaemorrhagic Escherichia coli (EHEC) serotype O157:H7, enteropathogenic E. coli (EPEC) serotype O111, E. coli K12 (a laboratory adapted non-pathogenic strain) and Salmonella enterica serotype Typhimurium was assayed on each cell type. For all adherence assays on all cell lines, EHEC O157:H7 adhered to a signi®cantly greater extent than the other bacteria. S. Typhimurium and EPEC O111 adhered to a similar extent to one another, whereas E. coli K12 was signi®cantly less adherent by 100-fold. In all cell types, >10% of adherent S. Typhimurium bacteria invaded, whereas c. 0.01±0.1% of adherent EHEC O157:H7 and EPEC O111 bacteria invaded, although they are regarded as non-invasive. EHEC O157 generated actin re-arrangements in all cell types as demonstrated by¯uorescent actin staining (FAS) under densely packed bacterial micro-colonies. EPEC O111 readily generated the localised adherent phenotype on bovine cells but generated only densely packed micro-colonies on HEp-2 cells. The intensity of actin re-arrangements induced in bovine cells by EPEC O111 was less than that induced by EHEC O157:H7. The intimate attachment on all cell types by both EHEC O157:H7 and EPEC O111 was clearly demonstrated by scanning electron microscopy.

Aim:To assess the effect of the growth promoter avilamycin on emergence and persistence of resistance in enteric bacteria in the pig. Methods and Results: Pigs (treated with avilamycin for 3 months and controls) were challenged with multiresistant Salmonella Typhimurium DT104 and faecal counts were performed for enterococci, Escherichia coli, S. Typhimurium and Campylobacter (before, during and 5 weeks post-treatment). Representative isolates were tested for antibiotic resistance and for the presence of resistance genes. Avilamycin-resistant Enterococci faecalis (speciated by PCR) were isolated from the treated pigs and continued to be detected for the first week after treatment had ceased. The avilamycin-resistance gene was characterized by PCR as the emtA gene and speciation by PCR. MIC profiling confirmed that more than one strain of Ent. faecalis carried this gene. There was no evidence of increased antimicrobial resistance in the E. coli, Salmonella and Campylobacter populations, although there was a higher incidence of tetB positive E. coli in the treated pigs than the controls. Conclusion: Although avilamycin selects for resistance in the native enterococci population of the pig, no resistant isolates were detected beyond 1 week post-treatment. This suggests that resistant isolates were unable to persist once selective pressure was removed and were out-competed by the sensitive microflora. Significance and Impact of the Study: Our data suggest the risk of resistant isolates becoming carcass contaminants and infecting humans could be minimized by introducing a withdrawal period after using avilamycin and prior to slaughter.