Identification of yeasts isolated from commercial shell eggs stored at refrigerated temperatures

Properties, Genetics and Innate Immune Function of the Cuticle in Egg-Laying Species

Cleidoic eggs possess very efficient and orchestrated systems to protect the embryo from external microbes until hatch. The cuticle is a proteinaceous layer on the shell surface in many bird and some reptile species. An intact cuticle forms a pore plug to occlude respiratory pores and is an effective physical and chemical barrier against microbial penetration. The interior of the egg is assumed to be normally sterile, while the outer eggshell cuticle hosts microbes. The diversity of the eggshell microbiome is derived from both maternal microbiota and those of the nesting environment. The surface characteristics of the egg, outer moisture layer and the presence of antimicrobial molecules composing the cuticle dictate constituents of the microbial communities on the eggshell surface. The avian cuticle affects eggshell wettability, water vapor conductance and regulates ultraviolet reflectance in various ground-nesting species; moreover, its composition, thickness and degree of coverage are dependent on species, hen age, and physiological stressors. Studies in domestic avian species have demonstrated that changes in the cuticle affect the food safety of eggs with respect to the risk of contamination by bacterial pathogens such as Salmonella and Escherichia coli. Moreover, preventing contamination of internal egg components is crucial to optimize hatching success in bird species. In chickens there is moderate heritability (38%) of cuticle deposition with a potential for genetic improvement. However, much less is known about other bird or reptile cuticles. This review synthesizes current knowledge of eggshell cuticle and provides insight into its evolution in the clade reptilia. The origin, composition and regulation of the eggshell microbiome and the potential function of the cuticle as the first barrier of egg defense are discussed in detail. We evaluate how changes in the cuticle affect the food safety of table eggs and vertical transmission of pathogens in the production chain with respect to the risk of contamination. Thus, this review provides insight into the physiological and microbiological characteristics of eggshell cuticle in relation to its protective function (innate immunity) in egg-laying birds and reptiles.

Effectiveness of Quaternary Ammonium in Reducing Microbial Load on Eggs

Table eggs are an affordable yet nutritious protein source for humans. Unfortunately, eggs are a vector for bacteria that could cause foodborne illness. This study aimed to investigate the effectiveness of a quaternary ammonium compound (quat) sanitizer against aerobic mesophilic bacteria, yeast, and mold load on the eggshell surface of free-range and commercial farms and the post-treatment effect on microbial load during storage. Total aerobic mesophilic bacteria, yeast, and molds were enumerated using plate count techniques. The efficacy of the quaternary ammonium sanitizer (quat) was tested using two levels: full factorial with two replicates for corner points, factor A (maximum: 200 ppm, minimum: 100 ppm) and factor B (maximum: 15 min, minimum: 5 min). Quat sanitizer significantly (p < 0.05) reduced approximately 4 log10 CFU/cm² of the aerobic mesophilic bacteria, 1.5 to 2.5 log10 CFU/cm² of the mold population, and 1.5 to 2 log10 CFU/cm² of the yeast population. However, there was no significant (p ≥ 0.05) response observed between individual factor levels (maximum and minimum), and two-way interaction terms were also not statistically significant (p ≥ 0.05). A low (<1 log10 CFU/cm²) aerobic mesophilic bacteria trend was observed when shell eggs were stored in a cold environment up to the production expiry date. No internal microbial load was observed; thus, it was postulated that washing with quat sanitizer discreetly (without physically damaging the eggshell) does not facilitate microbial penetration during storage at either room temperature or cold storage. Current study findings demonstrated that the quat sanitizer effectively reduced the microbial population on eggshells without promoting internal microbial growth.

Yeasts isolated from cloacal swabs, feces, and eggs of laying hens

Domestic and wild birds may act as carriers of human pathogenic fungi, although the role of laying hens in spreading yeasts has never been investigated. We evaluated the presence of yeasts in the cloaca (Group I, n = 364), feces (Group II, n = 96), and eggs (Group III, n = 270) of laying hens. The occurrence and the population size of yeasts on the eggshell, as well as in the yolks and albumens, were assessed at the oviposition time and during storage of eggs at 22 ± 1°C and 4 ± 1°C. A statistically higher prevalence and population size of yeasts were recorded in Group I (49.7% and 1.3 × 104 cfu/ml) and II (63.8% and 2.8 × 105 cfu/ml) than in Group III (20.7% and 19.9 cfu/ml). Candida catenulata and Candida albicans were the most frequent species isolated. Candida famata and Trichosporon asteroides were isolated only from the eggshells, whereas Candida catenulata was also isolated from yolks and albumens. During storage, the yeast population size on the shell decreased (from 37.5 to 8.5 cfu/ml) in eggs at 22 ± 1°C and increased (from 4.6 to 35.3 cfu/ml) at 4 ± 1°C. The laying hens harbor potentially pathogenic yeasts in their gastrointestinal tract and are prone to disseminating them in the environment through the feces and eggs. Eggshell contamination might occur during the passage through the cloaca or following deposition whereas yolk and albumen contamination might depend on yeast density on eggshell.

Development and validation of a TaqMan RT-PCR method for identification of mayonnaise spoilage yeast Pichia kudriavzevii

Food spoilage and its contamination with yeast and mold is a serious problem of food industry. Despite the high fat content, mayonnaise is an attractive substrate for food spoilage microorganisms. The aim of this study was to develop a method for yeast identification in mayonnaise and to test commercially available mayonnaises for the presence of these contaminating microorganisms. Based on the sequencing of intergenic regions ITS1 and ITS2, we identified a yeast microorganism that causes mayonnaise spoilage. We found that DNA sequences were more than 99% identical to the GenBank DNA sequences from Pichia kudriavzevii. We developed a specific to P. kudriavzevii TaqMan probe and primers. The reaction conditions were optimized regarding to the components concentration and temperature cycle. The minimum amount of P. kudriavzevii DNA that could be detected by developed method was 50 fg. The minimal number of P. kudriavzevii cells that could be detected by developed method without pre-enrichment was 50. We tested verified method with DNAs from microorganisms of different taxonomic groups that were obtained from three collections of microorganisms. Finally, we analyzed 20 different brands of mayonnaise from 14 producers and 10 different brands of mayonnaise sauce from seven producers. We determined the Cq parameter that characterizes transition of the fluorescence curve to the logarithmic phase and, therefore, correlates with the extent of sample contamination with P. kudriavzevii yeast. P. kudriavzevii was detected in six analyzed samples of mayonnaise and one sample of mayonnaise sauce.

Effects of vacuum packing on eggshell microbial activity and egg quality in table eggs under different storage temperatures

BACKGROUND

The aim of this study was to establish the effects of vacuum packing on eggshell microbial activity and egg quality traits in table eggs during 42 days of storage at 5 and 22 °C. Treatments were no vacuum packing (control) and vacuum packing (VP). Egg quality traits measured included egg weight loss, specific gravity, shell strength, albumen height, Haugh unit, yolk index, albumen pH, yolk pH, albumen colour and yolk colour.

RESULTS

VP eggs maintained higher specific gravity, albumen height, Haugh unit and yolk index and lower egg weight loss, albumen pH and yolk pH compared with control eggs after 42 days at 22 °C. VP eggs had lower levels of total aerobic mesophilic bacteria, Salmonella spp., Staphylococcus spp. and moulds/yeasts than control eggs over the storage period at both 5 and 22 °C. However, VP eggs had a higher level of coliforms than control eggs after 42 days at 5 °C.

CONCLUSION

The results indicated that vacuum packing extended the egg shelf life to at least 42 days compared with control eggs at 5 and 22 °C.