Viable Campylobacter jejuni on Eggshells and Its Potential to Cross-contaminate Egg White and Yolk When Using a Manual Separation Technique, Determined by Culture and Propidium Monoazide (PMA) qPCR

Abstract

Manual separation of egg yolk from egg white using the eggshell is common practice in private households. For this, the egg is cracked and both components are separated by passing the egg yolk back and forth between the two halves of the eggshell, allowing the egg white to drip down while the egg yolk remains in the shell. During this process, the egg content naturally gets in contact with the outside of the eggshell, which might lead to a cross-contamination with its microorganisms, thus was correspondingly assessed in this study. Campylobacter jejuni is one of the most important zoonotic pathogens that can be found on eggshells. Therefore, this bacterium was used to artificially contaminate the eggshells (n = 22) with concentrations of 3.1 ± 0.6 log10 cfu/g. After separating the egg yolk from the egg white, cross-contamination was determined using culture and qPCR. Altogether, cross-contaminations with C. jejuni were found in 15 egg white (68%) and in three egg yolk (14%) samples. Afterward, 90 eggs from 30 egg packs from different producers in and around Munich (Germany) were obtained for field study purposes. To address the problem of culturing due to a possible viable but nonculturable (VBNC) status of C. jejuni, a method to differentiate viable and dead C. jejuni on eggshell using 10 µM propidium monoazide (PMA) and qPCR was developed. As a result, seven egg packs (23%) were positive for C. jejuni. Of these, only one (3%) was contaminated with viable cells, but still in a concentration of 3.3 log10 cells/g shell. According to these results and considering that eggshells might also be naturally contaminated with other pathogens, the authors recommend avoiding the manual separation technique of egg white and yolk by the eggshell. Especially if raw egg white or yolk is used for preparation of not sufficiently heated foods, where contaminating pathogens are not inactivated during processing, this technique might be a safety hazard for the consumer.