Molecular analysis of the bacterial community in table eggs

Abstract

The composition of the bacterial flora on surfaces of table eggs is an important factor in influencing the incidence of egg spoilage. Previous studies have focused on a culturing approach for determining bacterial contamination of table eggs. The main problem, however, is culture-based techniques may not adequately describe the bacterial diversity of eggs, since many type of organisms are not cultivated by this method.

This study describes bacterial diversity of table eggs by using both culture-based and molecular approaches. The results of culture based techniques suggested that majority of eggs tested were contaminated with Staphylococcus species. No evidence was found for the presence of Salmonella, Escherichia coli, Campylobacter or Listeria monocytogenes, but Clostridium perfringens was found to be positive from 3 eggshells out of 16 shells tested. Methods for direct extraction of bacterial DNA from eggshell and egg content were developed. Cloning of PCR amplified rRNA resulted in the isolation of 91 clones which matched existing sequences in the GenBank database. Eighty-nine % of the isolates were matched to clones of the assigned phylotypes of Psychrobacter, Acinetobacter, Staphylococcus, Clostridium, Lactobacillus, Actinobacterium, Proteobacterium, Prevotella, Olsenella and Ralstonia. In addition Psychrobacter faecalis and Psychrobacter maritimus were isolated from eggshell on TSA at 4 °C, and the characteristics of these bacteria were studied. Interestingly, these bacteria have not been isolated from table eggs in previous studies, and they could potentially be responsible for egg spoilage particularly when the egg are stored in the fridge.

The results obtained in this study will provide valuable information to the egg producers and consumers that may aid improvement of the quality of table eggs and their shelf life. More importantly, it may facilitate the control of spreading these bacteria to the food chain, in order to prevent any food outbreaks that may result from consuming contaminated eggs.