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Table eggs are a vital dietary component owing to their nutritional value; however, bacterial contamination, particularly of eggshells, poses significant public health risks. In Sudan, these risks are exacerbated by inadequate hygiene, poor storage conditions, and limited regulatory oversight, which compromise egg safety in local markets. This preliminary, exploratory, cross-sectional, laboratory-based study aimed to evaluate bacterial contamination, assess physical characteristics, examine the pH of albumen and yolk, and investigate the associations among these factors in table eggs from Khartoum North. A total of 46 samples (three eggs per sample, totalling 138 eggs) were randomly collected from five types of retail outlets in Khartoum North in September 2020. Eggshell, albumen, and yolk samples were tested for aerobic bacterial contamination and total viable bacterial counts (TVC) using standard microbiological methods. Physical characteristics, including yolk colour, shell thickness, albumen height, shell strength, Haugh unit (HU), and albumen weight, were assessed using a Digital Egg Tester 6000, whereas pH levels were measured using a HI98107 pH meter. ANOVA and Pearson’s correlation were used to evaluate relationships, and Bayesian statistics were applied to estimate the pH values. Eggshell contamination by Staphylococcus spp. is widespread. (89.1%), Corynebacterium spp. (23.9%) being the most prevalent, followed by Escherichia coli (19.5%) and Salmonella spp. (15.2%). No bacteria were isolated from the albumen or yolk. A significant positive correlation was observed between the TVC and albumen pH ( r  = 0.540, P  < 0.001), whereas other internal traits showed weak, non-significant correlations. The physical classification identified Grade AA (32.6%), A (34.8%), and B (32.6%) eggs. Weak correlations were found between shell strength and HU ( r  = 0.155, 95% CI: −0.141 − 0.427, P  = 0.302) and between egg weight and HU ( r  = − 0.175, 95% CI: −0.434–0.121, P  = 0.244). ANOVA revealed no significant differences in shell strength ( F  = 2.622, P  = 0.084) or thickness ( F  = 0.115, P  = 0.892) across grades. Bayesian estimates showed slight pH increases from Grade AA to B in yolk (6.363–6.555; 95% CrIs: 6.135–6.791) and albumen (8.463–8.604; 95% CrIs: 8.013–9.071), but non-significant differences. However, the overlapping CrIs indicated that these differences were not significant. The presence of Staphylococcus and E. coli on eggshells indicates inadequate hygiene. Bacterial load is linked to albumen pH, indicating that external microbes influence internal composition. Quality variations were observed based on egg grade and source, with contamination undermining the internal defences. Albumen pH is an indicator of freshness. Monitoring the shells and conducting physicochemical tests could enhance the traditional methods. Policymakers must enforce standards to ensure the safety of eggs. Given the preliminary and exploratory nature of this study, coupled with the limitations of a small and uneven sample size, the findings should be interpreted with caution. These results are meant to generate hypotheses, highlighting the need for further research with larger, more representative samples, balanced sampling strategies, and more comprehensive methods. Such efforts are crucial for validating and expanding these observations and deepening our understanding of bacterial contamination and egg quality.

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.

In this study, we compared the antibacterial effectivity of the eggs of six precocial and four altricial bird species using Escherichia coli, based on their eggshell traits. The ultrastructure of eggshell was observed using a scanning electron microscope (SEM). According to SEM results, eggs from precocial birds (chicken, turkey, quail, duck, ostrich, and goose) had cuticle on the eggshells, while eggs from altricial birds (pigeon, budgerigar, munia, and canary) did not. The environment/selection pressure may induce the divergent evolution process in eggs of precocial and altricial birds. The E. coli experiment results showed that chicken, turkey, quail, duck, and goose eggs, with a high cuticle opacity, exhibited a much lower E. coli penetration rate. In contrast, the eggs with poor (ostrich) or without (pigeon, budgerigar, munia, and canary) cuticle exhibited a higher penetration rate. It is suggested that cuticle is a main barrier against bacterial penetration in precocial birds' eggs. Turkey and quail eggs showed the lowest E. coli contamination rate (3.33% and 2.22%, respectively), probably because of the tightly connected nanosphere structure on their cuticle. As for altricial birds' eggs, the eggs of budgerigar, munia, and canary with small pore diameter (0.57 to 1.22 μm) had a lower E. coli penetration rate than pigeon eggs (45.56%, 66.67%, 50%, and 97.78%, respectively, P < 0.05), indicating that pore diameter played a significant role in defending against bacterial trans-shell invasion. We found that eggshell thickness and pore area decreased with egg size. The cuticle quality had no relationship with egg size, but was closely related to the bird species. The E. coli penetration rate of altricial birds' eggs was significantly higher than that of precocial birds' eggs, mainly because the pores are exposed on the eggshell surface and cuticle protection is absent. This study provides detailed information on the eggshell cuticle, which gives insight into the cuticle evolution process that occurred in precocial and altricial bird species. Moreover, the results of E. coli penetration may help understanding the antibacterial behavior in birds.

Ten percent of all strong-evidence foodborne outbreaks in the European Union are caused by Salmonella related to eggs and egg products. UV light may be used to decontaminate egg surfaces and reduce the risk of human salmonellosis infections. The efficiency of continuous UV-C (254 nm) and pulsed UV light for reducing the viability of Salmonella Enteritidis, Listeria monocytogenes, and enterohemorrhagic Escherichia coli on eggs was thoroughly compared. Bacterial cells were exposed to UVC light at fluences from 0.05 to 3.0 J/cm2 (10 mW/cm2, for 5 to 300 s) and pulsed UV light at fluences from 1.25 to 18.0 J/cm2, resulting in reductions ranging from 1.6 to 3.8 log, depending on conditions used. Using UV-C light, it was possible to achieve higher reductions at lower fluences compared with pulsed UV light. When Salmonella was stacked on a small area or shielded in feces, the pulsed UV light seemed to have a higher penetration capacity and gave higher bacterial reductions. Microscopy imaging and attempts to contaminate the interior of the eggs with Salmonella through the eggshell demonstrated that the integrity of the eggshell was maintained after UV light treatments. Only minor sensory changes were reported by panelists when the highest UV doses were used. UV-C and pulsed UV light treatments appear to be useful decontamination technologies that can be implemented in continuous processing.

Birds host diverse bacterial assemblages, which play a critical role in individual health, but which can also lead to disease or mortality. It is therefore important for developing embryos to acquire appropriate bacterial communities from maternal (vertical transmission) and environmental (horizontal transmission) sources. Eggshell bacterial assemblages are acquired before and after oviposition, and are shaped by external factors, including habitat, nesting material and parental incubation. Understanding the source of eggshell bacteria is important, because eggshell penetration of horizontally-transmitted bacteria can affect embryonic health. Most research on eggshell-associated bacteria has occurred on ‘dry-nesting’ terrestrial birds. However, little is known on bacterial acquisition in waterbirds, particularly in nests where eggs are in direct contact with water. Moist environments favour bacterial growth and wet-nesting species are therefore expected to have higher bacterial loads. To date, no study has focussed on contrasting the abundance and diversity of eggshell bacterial assemblages in wet- and dry-nesting species. We used both bacterial culture and genetic techniques (automated ribosomal intergenic spacer analysis) to document the bacterial load and assemblage structure of eggshell-associated bacteria in both wet- and dry-nesting wetland-associated bird species. Bacterial loads were several orders of magnitude greater on eggs of wet-nesting species and bacterial assemblages tended to cluster by nesting strategy. These findings suggest a possible association of eggshell-associated bacteria with nesting strategies in these species. Further research is, however, required to confirm these patterns, incorporating more comprehensive sampling and utilising more advanced genetic approaches. Overall, our findings highlight a promising direction for future research into the association between nesting in moist environments and eggshell-associated bacteria, as well as the potential for antimicrobial adaptations that may characterise the eggshells of these species.

The microbiome is essential for development, health and homeostasis throughout an animal’s life. Yet, the origins and transmission processes governing animal microbiomes remain elusive for non-human vertebrates, oviparous vertebrates in particular. Eggs may function as transgenerational carriers of the maternal microbiome, warranting characterisation of egg microbiome assembly. Here, we investigated maternal and environmental contributions to avian eggshell microbiota in wild passerine birds: woodlark Lullula arborea and skylark Alauda arvensis . Using 16S rRNA gene sequencing, we demonstrated in both lark species, at the population and within-nest levels, that bacterial communities of freshly laid eggs were distinct from the female cloacal microbiome. Instead, soil-borne bacteria appeared to thrive on freshly laid eggs, and eggshell microbiota composition strongly resembled maternal skin, body feather and nest material communities, sources in direct contact with laid eggs. Finally, phylogenetic structure analysis and microbial source tracking underscored species sorting from directly contacting sources rather than in vivo-transferred symbionts. The female-egg-nest system allowed an integrative assessment of avian egg microbiome assembly, revealing mixed modes of symbiont acquisition not previously documented for vertebrate eggs. Our findings illuminated egg microbiome origins, which suggested a limited potential of eggshells for transgenerational transmission, encouraging further investigation of eggshell microbiome functions in vertebrates.

Salmonella is an important foodborne pathogen, causing an estimated 11,992 cases of infection in Australia per year. Egg or egg product related salmonellosis is a major concern for the egg industry. Worldwide, S. Typhimurium is one of the most common serovars identified in Salmonella food poisoning cases. The current study investigated the ability of five S. Typhimurium strains to penetrate washed and unwashed eggs using whole egg and agar egg penetration methods. All S. Typhimurium strains were able to penetrate eggshells and survive in egg albumen (at 20°C) according to whole egg penetration results. Polymerase Chain Reaction results demonstrated that S. Typhimurium strain 2 (10(3) and 10(5) CFU/mL), and strain 5 (10(3) and 10(5) CFU/mL) egg penetration was significantly higher (p<0.05) in washed eggs when compared to unwashed eggs. Statistical analysis of the agar penetration experiment indicated that S. Typhimurium was able to penetrate washed eggs at a significantly higher rate when compared to unwashed eggs (p<0.05). When compared to unwashed eggs, washed eggs also had significantly damaged cuticles. Statistical analysis also indicated that eggshell penetration by S. Typhimurium was related to various eggshell ultrastructural features such as cap quality, alignment, erosion, confluence, Type B bodies and cuticle cover.

An innovative method is introduced based on the combination of label-free surface-enhanced Raman scattering with advanced multivariate analysis. This technique allows both quantitative and qualitative assessment of Salmonella typhimurium and Escherichia coli  on eggshells. Using silver nanocubes embedded in polydimethylsiloxane, we consistently achieved Raman spectra of bacteria. The stability of the Ag NCs@PDMS substrate is confirmed using rhodamine 6G over 30 days under standard conditions. Principal component analysis (PCA) effectively distinguishes between S. typhimurium and E. coli spectra. Partial least squares regression (PLS) models were developed for quantitative determination of bacteria on egg surfaces, yielding accurate results with minimal error. The S. typhimurium model achieves R c 2  = 0.9563 and RMSEC = 0.601 in calibration, and R v 2  = 0.9113 and RMSEV = 0.907 in validation. Similarly, the E. coli model achieves R c 2  = 0.9877 and RMSEC = 0.322 in calibration, and R v 2  = 0.9606 and RMSEV = 0.579 in validation. Recoveries validate PLS predictions by inoculating egg surfaces with varying bacterial amounts. Our study demonstrates the feasibility of SERS-PLS for quantitative determination of S. typhimurium and E. coli on eggshells, promising enhanced food safety protocols. Graphical Abstract

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.

The objective of this work was to study the effect of tea tree (TTO) and lavender (LavO) essential oils instead of formaldehyde fumigation to disinfect the surface of fertilized eggshells. A total of 1050 fresh unwashed fertilized quail eggs were randomly divided into 7 groups and treated before incubation as follows: group 1 was untreated (negative control), group 2 was sprayed with 70% ethyl alcohol (positive control), group 3 was fumigated with formaldehyde gas (FF), groups 4–5 and 6–7 were sprayed with 2%, 3% TTO and 2%, 3% LavO, respectively. Spraying fertilized eggs with 3% TTO or LavO significant reduced ( P  < 0.05) egg weight loss and improved yolk sac absorption expressed as a decrease in the yolk sac remaining weight ( P  < 0.01), which coincided with increasing the percentage of embryonic weight at 14th day of incubation compared to the FF. TTO or LavO significantly boosted the hatching rate that correlated with significant reduction ( P  < 0.01) in embryonic mortality with preference for LavO. Spraying fertilized eggs immediately after collection with TTO or LavO significantly reduced ( P  < 0.01) total bacterial count on the eggshell surface compared to the FF. Thus, TTO and LavO can be used to disinfect fertilized eggs prior to incubation to improve hatching rates and chicks’ quality upon hatching.