A comparative study on the pathogenesis of egg contamination by different serotypes ofSalmonella

Abstract

Salmonella enterica serotype Enteritidis is the predominant serotype associated with egg-borne salmonellosis in humans. Apparently this serotype possesses particular characteristics that increase its chance to contaminate eggs. To identify these characteristics, two Salmonella serotype Enteritidis strains as well as one strain of each of the serotypes Salmonella Typhimurium, Salmonella Heidelberg, Salmonella Virchow and Salmonella Hadar strain were used to examine different aspects related to egg contamination. After an intravenous infection of laying hens, it was observed that the ability of the serotype Enteritidis strains to colonize the reproductive organs was significantly higher compared with the Salmonella Heidelberg, Salmonella Virchow and Salmonella Hadar strains but not with the Salmonella Typhimurium strain. Inoculating low numbers of the different Salmonella serotypes in egg albumen at 42 degrees C demonstrated that the growth of the strains belonging to the Salmonella serotypes Virchow and Hadar was seriously repressed. The other serotypes, however, survived in albumen for 24 h. Furthermore, using two different specifically designed egg infection models, it was shown that all strains used in this study were able to penetrate into and multiply inside the yolk at 25 degrees C. These findings indicate that the ability to grow in eggs post lay is not specific for the serotype Enteritidis. In conclusion, comparing strains belonging to different Salmonella serotypes has revealed that most probably a preferential colonization of the reproductive organs and an enhanced survival at 42 degrees C allows the serotype Enteritidis to contaminate eggs.

Avaliação da resposta imunológica da mucosa intestinal de frangos de corte desafiados com diferentes sorovares de Salmonella

“…Eles assumiram posição média na imunogenicidade e no efeito em desempenho das aves inoculadas. Estes dados estão de acordo com o trabalho comparativo de Gantois et al (2008) que indicaram maior capacidade de colonização dos órgãos reprodutores da SE e ST em relação a outros sorovares estudados. Aparentemente alguns sorovares possuem características particulares que aumentam a chance de infectar as aves causando perdas zootécnicas levando a um maior estímulo do sistema imune da ave. Conclui-se que existe uma relação entre a intensidade de estímulo do sistema imunológico e o gasto energético dos animais, sendo que microrganismos mais patogênicos repercutem em menor ganho de peso das aves em função do custo para a formação da defesa linfocitária de mucosa.…”

Scientific Opinion on the public health risks of table eggs due to deterioration and development of pathogens

“…Studies have shown that some S. Enteritidis phage types (PTs) are more invasive than others (Hinton et al, 1990;Roy et al, 2001), but other similarly designed studies could not identify any difference in the invasiveness or colonisation ability between different phage types (Barrow, 1991). Despite its peculiar affinity for the reproductive tract of hens, S. Enteritidis is not the only serotype able to colonise ovaries and oviducts and contaminate forming eggs (Keller et al, 1997;Okamura et al, 2001a;Gast et al, 2004;Gantois et al, 2008).…”

“…Enteritidis is particularly successful in invading the hen reproductive tract and contaminating eggs (Humphrey, 1994;Okamura et al, 2001a;Okamura et al, 2001b;Gast et al, 2004;Gantois et al, 2008). The success of S. Enteritidis in the transovarian transmission route can be associated with the presence in this serovar of the SEF14 fimbriae (which might be involved in the colonization of the reproductive organs), the presence of the yafD gene (which is essential for resistance in the albumen), and with the lipopolysaccharide structure, a key factor in oviduct persistence and survival in egg albumen (Lu et al, 2003;Coward et al, 2013), particularly at a hen body temperature of 41.5 °C (Coward et al, 2013).…”

“…Other Salmonella serovars are rarely isolated from egg contents, but can infect the hen reproductive organs (Okamura et al, 2001a;Gast et al, 2004;Martelli and Davies, 2012). In an intravenous infection study, S. Heidelberg was demonstrated to be able to survive in the albumen during egg formation, while S. Virchow and S. Hadar were eliminated more rapidly, suggesting that, in natural infections, they might be killed in the albumen before ovodeposition (Gantois et al, 2008).…”

“…Forming eggs have been shown to have a higher contamination rate than laid ones, as the egg albumen contains antibacterial compounds that reduce the bacterial load over time (Keller et al, 1995). Salmonella cannot replicate effectively in the albumen of fresh eggs, and therefore must gain access to the yolk contents in order to multiply (Gantois et al, 2008). The vitelline membrane in fresh eggs inhibits yolk invasion by Salmonella, but gradually this deteriorates during storage, leading to penetration in the egg yolk (Humphrey and Whitehead, 1993).…”