Survey of 'Enterobacteriaceae' contamination of table eggs collected from layer flocks in Australia

In the present study, eggs from commercial caged layer flocks at different stages of lay in Australia were collected. 'Enterobacteriaceae' populations from eggshell surface and eggshell pore were enumerated and these populations characterized using API® Rapid 20E strips. The eggshell surface, eggshell pore and egg internal content samples were also processed for the isolation of 'Salmonella' and these isolates were tested for the presence or absence of several virulence genes (prgH, sopB, spiC, orfL, invA, sifA, sitC, misL). Results indicated that there was no significant difference in total 'Enterobacteriaceae' count on the eggs of the flock from early, mid or late lay flocks. 'Enterobacteriaceae' isolates were of 11 different genera which included: 'Cedecea', 'Citrobacter', 'Enterobacter', 'Escherichia', 'Klebsiella', 'Kluyvera', 'Leclercia', 'Pantoea', 'Salmonella', 'Serratia' and 'Yersinia'. Out of all 153 identified 'Enterobacteriaceae' isolates, the 'Escherichia' genus was reported most frequently (60.78%). Results also indicated that overall there were 4.51% (14/310) 'Salmonella' positive pooled samples. In this study, 14 'Salmonella' strains were isolated, serotyping confirmed that 12 out of them were 'Salmonella' Infantis and the 2 others were 'Salmonella enterica' subsp. 'enterica' serovar 4,12:d: Polymerase chain reaction results indicated that all 'Salmonella' Infantis isolates harboured 'invA', 'misL', 'orfL', 'prgH', 'sifA', 'sitC', 'SopB' and 'spiC' genes which suggests that Salmonella Infantis strains isolated from eggshell surface may have the capacity to invade and survive in macrophages.