Isolation of Salmonella enterica in Laying-Hen Flocks and Assessment of Eggshell Contamination in France

Abstract

The present investigation was conducted in conjunction with the European Union baseline study for the estimation of Salmonella prevalence in laying-hen flocks. It aimed at evaluating eggshell contamination in farms positive for Salmonella, characterizing the genetic patterns of Salmonella strains and identifying the factors associated with Salmonella contamination of eggshells. For this purpose, a total of 4,200 eggs were collected from 28 positive flocks and analyzed according to draft Annex D of International Organization for Standardization Method 6579. Molecular characterization of the Salmonella strains was obtained by the pulsed-field gel electrophoresis method with two restriction enzymes, XbaI and BlnI. The relationship between the presence of Salmonella on eggshells and rearing practices was studied by using multiple correspondence analysis. Results showed that 39.3% of the positive flocks had at least one positive eggshell, with a total of 1.05% of eggshells testing positive for Salmonella. We detected the same serovars on samples taken from the farm and from eggshells within a given flock, with isolates sharing the same genetic pattern in 7 of 11 flocks. Eggshells tested positive for Salmonella in flocks (i) located where delivery trucks pass near air entrances of the poultry house, (ii) with high holding capacity (>30,000 laying hens), and (iii) with more than five positive samples coming from the farm environment, as well as in cases of flocks with a maximum egg-laying rate of >96% and in cases where farmers worked in other animal production. This study provided valuable information that could be used for risk management and risk assessment studies.

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

“…Field studies have found a correlation between the number of positive environmental samples and the proportion of eggs positive in a flock (Kinde et al, 1996;Davies and Breslin, 2004;Chemaly et al, 2009;Renu and Tripathi, 2011), suggesting that prevalence of infection and on-farm hygiene are directly related to the number of contaminated eggs produced (Arnold et al, 2014b). Eggshell contamination occurs more frequently than the contamination of the egg contents Davies and Breslin, 2004;Little et al, 2007b;Little et al, 2008).…”

“…S. Senftenberg, S. Livingstone, S. Infantis) are occasionally isolated from eggs, mainly from eggshells, but also rarely from egg contents (Martelli and Davies, 2012). S. Infantis has been isolated from eggs in several surveys carried out in Europe ((de Louvois, 1993;Little et al, 2007a;Murchie et al, 2007;Wilson, 2007;Chemaly et al, 2009;Martelli and Davies, 2012). S. Infantis is also associated with egg and human illness in geographical areas outside Europe, such as Japan and New Zealand (Lapuz et al, 2008;Wilson, 2007).…”

“…Specific risk factors associated with Salmonella contamination of eggshells in one study were entry of delivery trucks near poultry house entrance, flock size, heavily contaminated environment, high egg laying rate and mixed farming (Chemaly et al, 2009). …”

Scientific Opinion on a quantitative estimation of the public health impact of setting a new target for the reduction of Salmonella in laying hens

“…Other serovars i.e. S. Mbandaka, S. Heidelberg, S. Hadar, S. Infantis and S. Virchow, could also occur with low frequency in layers and consequently on egg surfaces (Chemaly et al, 2009). Their occurrence varies greatly between continents and countries (Poppe, 1992;Snow et al, 2007;EFSA, 2007).…”

“…In Austria, the factor associated with Salmonella status was cage housing (Much et al, 2007). In France, RFs associated with Salmonella contamination of eggshells were; entry of delivery trucks near the poultry house entrance, flock size, more than five culture positive environmental samples, high egg-laying rate and mixed farming (Chemaly et al, 2009). …”