Evaluation of the influence of the housing system on bacterial egg and environmental contamination in Italy.

The aim of this surveillance, performed along the whole laying hen cycle, has been to compare the bacterial contamination of 302 environment and egg samples collected in 2 conventional cage systems (N=186) and in 3 organic farms (N=116) in Italy. Total counts of aerobic bacteria and Enterobacteriaceae, as well as presence of Salmonella, with particular focus on the serotype Enteritidis, have been investigated on environmental swabs and dusts as well as on eggshells and on edible part of egg sampled at the hen age of 24, 48 and 72 weeks. The data were analysed by ANOVA using the GLM procedure of SAS (1989). The rate of Salmonella positive samples observed among environmental swabs and dusts, faeces, eggshells and edible part of eggs collected in conventional cage and organic systems did not show any statistically significative difference. The samples more frequently contaminated by Salmonella have been environmental dusts in both organic and conventional houses (i.e. 11.1 and 6.6%) as well as on faeces (i.e. 9.5 and 8%). Eggs with Salmonella positive eggshells were collected only within organic production units whereas their edible parts were Salmonella negative. This result demonstrated the inhibitory efficacy of antimicrobial enzymatic systems of the inner egg able to reduce the aerobic bacteria and Enterobacteriaceae which were always lower than the detection limits, corresponding to 10 and 1 colony forming unit (CFU) per g, respectively. Overall, total aerobic counts on both environmental samples and eggshells did not show a statistically significant increase over time. In fact, they ranged between 4.82 and 5.18 Log10 CFU/g and between 4.65 and 4.75 Log10 CFU/g within organic and conventional cage houses, respectively. The same trend has been observed for the Enterobacteriaceae total counts, ranging between 1.83 and 1.92 Log10 CFU/g and between 2.16 and 2.43 Log10 CFU/g within organic and conventional cage houses, respectively. These values justify the low rate of Salmonella contamination and agree with those described in literature. The total aerobic counts on environmental dusts sampled within organic and conventional cage houses did not show any statistical differences, whereas the Enterobacteriaceae count on environmental dusts sampled within organic units has been statistically lower than that observed in conventional cage houses (i.e. 3.45 vs 5.19 Log10 CFU/g). On the contrary, the total aerobic and Enterobacteriaceae counts on eggshells of eggs collected within organic and conventional cage houses did not show any statistical difference. In conclusion, from an environmental point of view, the overall microbial contamination is lower in the organic system, whereas the rate of Salmonella resulted higher in the eggshells of organic eggs. This result may be attributable to a higher incidence of dirty eggs, mainly contaminated with faeces, therefore improvements in hygienic management procedures might increase the egg safety.