Occurrence of gram-negative bacteria in hens' eggs depending on their source and storage conditions

The aim of this study was to analyse the qualitative composition of Gram-negative microbes, mainly of the family Enterobacteriaceae, including pathogenic bacteria such as Salmonella, in the albumens and yolks and on the shells of hens' eggs, depending on their source and on the temperature and duration of their storage. A total of 375 table eggs were studied, from a large-scale poultry farm, a small-scale poultry farm and a supermarket. Each group was divided into 5 subgroups according to the temperature and duration of their storage during the study. Two serotypes of bacteria of the genus Salmonella were identified: S. Enteritidis and S. Arizonae. Strains of Salmonella spp. were also isolated. Apart from Salmonella and Escherichia coli, among the most frequently isolated bacteria of the family Enterobacteriaceae were Enterobacter spp., Klebsiella spp. and Citrobacter freundii. Qualitative analysis of the bacterial microflora of the eggs also showed the presence of other Gram negative bacteria, including Acinetobacter spp., Pseudomonas spp., Tatumella ptyseos, Providencia stuartii, Serratia liquefaciens, Flavimonas oryzihabitans, Vibrio metschnikovii, Leclercia adecarboxylata, Kluyvera spp., Rahnella aquatilis, Proteus mirabilis, and Achromobacter spp. The study demonstrated that the conditions applied, i.e., the temperature and duration of storage, did not significantly influence the prevalence of particular species of Gram-negative bacteria in the eggs. However, based on the analysis of contamination of eggs with Salmonella depending on their source, it can be concluded that the system in which the hens are housed affects the risk of contamination of eggs with these pathogens.