Effect of egg washing and correlation between cuticle and egg penetration by various Salmonella strains

Development of Cracked Egg Detection Device Using Electric Discharge Phenomenon

Eggs are a highly nutritious food; however, those are also fragile and susceptible to cracks, which can lead to bacterial contamination and economic losses. Traditional methods for detecting cracks, particularly in processed eggs, often fall short due to changes in the eggs' physical properties during processing. This study was aimed at developing a novel device for detecting egg cracks using electric discharge phenomena. The system was designed to apply a high-voltage electric field to the eggs, where sparks were generated at crack locations due to the differences in electrical conductivity between the insulative eggshell and the more conductive inner membrane exposed by the cracks. The detection apparatus consisted of a custom-built high-voltage power supply, flexible electrode pins, and a rotation mechanism to ensure a complete 360-degree inspection of each egg. Numerical simulations were performed to analyze the distribution of the electric field and charge density, confirming the method's validity. The results demonstrated that this system could efficiently detect cracks in both raw and processed eggs, overcoming the limitations of existing detection technologies. The proposed method offers high precision, reliability, and the potential for broader application in the inspection of various poultry products, representing a significant advancement in food safety and quality control.

Characterization and evaluation of anti-Salmonella enteritidis activity of indigenous probiotic lactobacilli in mice

Lactobacilli (n = 24), isolated from human infants and yogurt, showed variable in vitro activity against Salmonella enteritidis (8.0 ± 1.0 to 16.6 ± 0.5 mm) and other gut pathogens (9.0 ± 1.0 to 15.3 ± 0.5 mm), as determined by a well diffusion assay. The isolates were identified as Limosilactobacillus fermentum (FY1, FY3, FY4, IL2, and IL5), Lactobacillus delbrueckii (FY6 and FY7), Lactobacillus sp. (IL7), and Lactobacillus gasseri (IL12). All isolates showed variable in vitro tolerance to acidic pH for 3 h and visible growth at pH 4 and in the presence of 0.3% ox-bile. The antibiotic susceptibility profile of Lactobacillus isolates indicated resistance against vancomycin, ciprofloxacin, streptomycin, and lincomycin. Isolates had variable auto-aggregation and showed variable capabilities to co-aggregate with S. enteritidis. Based on all tested parameters, L. fermentum IL2, L. fermentum IL5, and L. gasseri IL12 were selected for co-culture experiments, followed by in vivo evaluation in Balb/c mice. All the selected isolates resulted in a 100% reduction in S. enteritidis in broth. Lactobacillus isolates efficiently colonized mouse guts and inhibited S. enteritidis colonization. Overall, there was ≥99.06% and ≤4.32 Mean log₁₀ reduction in Salmonella counts in mice feces within 7 days. The study, thus, provided characterized lactobacilli that could be considered as potential ingredients for probiotic formulations intended to prevent S. enteritidis infection in humans.

Impact of Different Layer Housing Systems on Eggshell Cuticle Quality and Salmonella Adherence in Table Eggs

The bacterial load on the eggshell surface is a key factor in predicting the bacterial penetration and contamination of the egg interior. The eggshell cuticle is the first line of defense against vertical penetration by microbial food-borne pathogens such as Salmonella Enteritidis. Egg producers are increasingly introducing alternative caging systems into their production chain as animal welfare concerns become of greater relevance to today’s consumer. Stress that is introduced by hen aggression and modified nesting behavior in furnished cages can alter the physiology of egg formation and affect the cuticle deposition/quality. The goal of this study was to determine the impact of caging systems (conventional, enriched, free-run, and free-range), on eggshell cuticle parameters and the eggshell bacterial load. The cuticle plug thickness and pore length were higher in the free-range eggs as compared to conventional eggs. The eggshells from alternative caging (enriched and free-range) had a higher total cuticle as compared to conventional cages. A reduction in bacterial cell counts was observed on eggshells that were obtained from free-range eggs as compared to the enriched systems. An inverse correlation between the contact angle and Salmonella adherence was observed. These results indicate that the housing systems of layer hens can modify the cuticle quality and thereby impact bacterial adherence and food safety.

Effect of Storage Temperature on the Survival of New Zealand Egg-Associated Salmonella Isolates in and on Eggs

The influence of egg storage temperature on Salmonella contamination of eggs is a key consideration in determining storage and shelf life recommendations for eggs. In this study, experiments assessed the survival of Salmonella isolates on and in eggs at storage temperatures (15 and 22°C) currently used in New Zealand. Eggshell surfaces were inoculated with a cocktail of 10 Salmonella isolates comprising five serotypes, at a concentration of ∼10⁶ CFU per egg (for determining shell surface survival) or ∼10³ CFU per egg (for determining internalization). Additionally, a subset of eggs was artificially contaminated with sterile chicken feces prior to Salmonella inoculation. Inoculated eggs were incubated at 15 and 22°C. At 0, 21, and 35 days of incubation, eggshells were enumerated for Salmonella, and egg contents were tested for Salmonella presence or absence (yolk) or most probable number (albumen). Higher levels of Salmonella were recovered from eggshells following incubation at 15°C (31% relative humidity [RH]) compared with 22°C (45% RH) after both 21 and 35 days of incubation. Recoverable numbers of Salmonella from visibly clean eggshell surfaces declined over time at both storage temperatures and were at, or below, the limit of detection from eggs stored at 22°C and 45% RH for 35 days. A substantially higher concentration of viable Salmonella was recovered from eggshells that were experimentally contaminated with chicken feces compared with those without, particularly from eggs stored at 15°C and 31% RH for 35 days (2.38 log higher CFU from eggs containing feces). No Salmonella was detected in egg contents (albumen or yolk) at any incubation temperature or time point, regardless of the presence of feces. Findings emphasize the importance of current regulations that require eggs sold at retail to be visibly clean and will inform risk management decisions regarding egg storage times and temperatures with respect to Salmonella control in and on New Zealand eggs at retail.

Salmonella on Australian cage egg farms: Observations from hatching to end of lay

Single-aged caged layer hen flocks were monitored for Salmonella over the course of their lifetime. Chicks from both flocks were Salmonella negative at hatch and remained negative during rearing. Pullets were transported to production farms at 15 weeks of age. Pre-population dust swabs collected from both production sheds had a high percentage of Salmonella positive samples (80 and 90%). Flocks were sampled at regular intervals until 70-72 weeks of age. The proportion of Salmonella positive samples and mean load detected on eggs was low on both farms. Analysis of dust samples revealed that Salmonella persisted in dust over 8 weeks. Dust total moisture content and water activity appears to influence bacterial persistence. On egg grading equipment, only suction cups prior to egg washing were Salmonella positive (mean proportion Salmonella positive samples 0.13 ± 0.07; mean load of 18.6 ± 12.31 MPN/ml). An egg washing experiment demonstrated that while washing reduced the total Salmonella load from eggshell surfaces, no effect was observed for shell pores. These results demonstrate that despite environmental contamination on farm, Salmonella contamination of eggs is low and is further minimized by washing.

Non-typhoidal Salmonella contamination in egg shells and contents from retail in Western Australia: Serovar diversity, multilocus sequence types, and phenotypic and genomic characterizations of antimicrobial resistance

In recent years, the number of human salmonellosis cases in Western Australia (WA) has increased more dramatically than in any other Australian state. In 2017, the number of cases in WA was more than double the five-year average, and eggs had emerged as the key culprit for several Salmonella foodborne disease outbreaks. To better understand such an epidemiologically intriguing situation, our research goal was to investigate the prevalence, serovar diversity, multilocus sequence types, and antimicrobial resistance of non-typhoidal Salmonella contamination in retail eggs produced and sold in WA. A total of 200 visually clean and intact retail egg samples (each containing a dozen eggs) were purchased for one year (2017-2018) from supermarkets in metropolitan Perth, the capital of WA. For each sample, the contents and shells of the 12 eggs were separately pooled and cultured according to standard methods. Overall, Salmonella was detected in 11.5% (23/200) of the tested egg samples. Salmonella was isolated from 4.5% (9/200) and 3% (6/200) of eggshells and egg contents, respectively. In 4% (8/200) of the samples, Salmonella was recovered from both eggshell and egg contents. Isolates from positive retail egg samples were serotyped as either S. Typhimurium (52.2% [12/23]) or S. Infantis (39.1% [9/23]). Both serotypes were concurrently recovered from two different retail egg samples. We retained a set of both S. Typhimurium (n = 29) and S. Infantis (n = 12) isolates from all Salmonella-positive retail packs (n = 23) for further characterization. Only two (S. Typhimurium) isolates showed resistance to ampicillin, of which one carried β-lactamase resistance gene bla_TEM-1b. The remaining isolates (39/41) were susceptible to all 14 antimicrobials included in the minimum inhibitory concentrations (MICs) testing panel. Multilocus sequence typing and serotyping were perfectly mirrored, as all S. Typhimurium isolates were characterized as sequence type (ST)-19, and all S. Infantis isolates were ST-32. This study points to the noteworthy Salmonella prevalence rate in retail egg samples in WA. Our results illustrate minimal public health risks arising from antimicrobial resistance Salmonella from Australian eggs.

Comparative study of eggshell antibacterial effectivity in precocial and altricial birds using Escherichia coli

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.

Common guillemot (Uria aalge) eggs are not self-cleaning

Birds are arguably the most evolutionarily successful extant vertebrate taxon, in part because of their ability to reproduce in virtually all terrestrial habitats. Common guillemots, Uria aalge, incubate their single egg in an unusual and harsh environment; on exposed cliff ledges, without a nest, and in close proximity to conspecifics. As a consequence, the surface of guillemot eggshells is frequently contaminated with faeces, dirt, water and other detritus, which may impede gas exchange or facilitate microbial infection of the developing embryo. Despite this, guillemot chicks survive incubation and hatch from eggs heavily covered with debris. To establish how guillemot eggs cope with external debris, we tested three hypotheses: (1) contamination by debris does not reduce gas exchange efficacy of the eggshell to a degree that may impede normal embryo development; (2) the guillemot eggshell surface is self-cleaning; (3) shell accessory material (SAM) prevents debris from blocking pores, allowing relatively unrestricted gas diffusion across the eggshell. We showed that natural debris reduces the conductance of gases across the guillemot eggshell by blocking gas exchange pores. Despite this problem, we found no evidence that guillemot eggshells are self-cleaning, but instead showed that the presence of SAM on the eggshell surface largely prevents pore blockages from occurring. Our results demonstrate that SAM is a crucial feature of the eggshell surface in a species with eggs that are frequently in contact with debris, acting to minimise pore blockages and thus ensure a sufficient rate of gas diffusion for embryo development.

Inactivation of Salmonella on Eggshells by Chlorine Dioxide Gas

Microbiological contamination of eggs should be prevented in the poultry industry, as poultry is one of the major reservoirs of human Salmonella. ClO2 gas has been reported to be an effective disinfectant in various industry fields, particularly the food industry. The aims of this study were to evaluate the antimicrobial effect of chlorine dioxide gas on two strains of Salmonella inoculated onto eggshells under various experimental conditions including concentrations, contact time, humidity, and percentage organic matter. As a result, it was shown that chlorine dioxide gas under wet conditions was more effective in inactivating Salmonella Enteritidis and Salmonella Gallinarum compared to that under dry conditions independently of the presence of organic matter (yeast extract). Under wet conditions, a greater than 4 log reduction in bacterial populations was achieved after 30 min of exposure to ClO2 each at 20 ppm, 40 ppm, and 80 ppm against S. Enteritidis; 40 ppm and 80 ppm against S. Gallinarum. These results suggest that chlorine dioxide gas is an effective agent for controlling Salmonella, the most prevalent contaminant in the egg industry.

Comparative phenotypic and genotypic virulence of Salmonella strains isolated from Australian layer farms

There are over 2500 Salmonella enterica serovars that circulate globally. Of these, serovars those classified into subspecies I are the most common cause of human salmonellosis. Many subspecies I Salmonella serovars are routinely isolated from egg farm environments but are not frequently associated with causing disease in humans. In this study, virulence profiles were generated for 10 strains of Salmonella enterica isolated directly from egg farm environments to investigate their potential public health risk. Three virulence parameters were assessed including in vitro invasion, in vivo pathogenicity and characterization of genomic variation within five specific pathogenicity islands. These 10 Salmonella strains exhibited significant differences in invasion into the human intestinal epithelial cell line, Caco2. Low, moderate, and high invasion patterns were observed and the degree of invasion was dependent on bacterial growth in a nutritive environment. Interestingly, two Salmonella strains, S. Adelaide and S. Bredeney had consistently low invasion. The S. Typhimurium definitive types and S. Virchow exhibited the greatest cell invasion following growth in Luria Bertani broth. Only the S. Typhimurium strains caused disease in BALB/c mice, yet the majority of serovars were consistently detected in feces over the 21 day experiment. Genomic comparison of the five specific pathogenicity islands has shown that variation in virulence is likely multifactorial. Sequence variability was observed primarily in strains with low virulence. In particular, genes involved in forming the structures of the SPI-1 and SPI-2 type 3 secretion systems as well as multiple effector proteins were among the most variable. This variability suggest that serovars with low virulence are likely to have both invasion and within host replication defects that ultimately limit their pathogenicity.