Dataset Information

Predictive Modeling for the Growth of Salmonella spp. in Liquid Egg White and Application of Scenario-Based Risk Estimation.

ABSTRACT: The objective of the study was to develop a predictive model of Salmonella spp. growth in pasteurized liquid egg white (LEW) and to estimate the salmonellosis risk using the baseline model and scenario analysis. Samples were inoculated with six strains of Salmonella, and bacterial growth was observed during storage at 10-37 °C. The primary models were developed using the Baranyi model for LEW. For the secondary models, the obtained specific growth rate (μmax) and lag phase duration were fitted to a square root model and Davey model, respectively, as functions of temperature (R2 ≥ 0.98). For μmax, the values were satisfied within an acceptable range (Af, Bf: 0.70-1.15). The probability of infection (Pinf) due to the consumption of LEW was zero in the baseline model. However, scenario analysis suggested possible salmonellosis for the consumption of LEW. Because Salmonella spp. proliferated much faster in LEW than in egg white (EW) during storage at 20 and 30 °C (p < 0.01), greater Pinf may be obtained for LEW when these products are stored at the same conditions. The developed predictive model can be applied to the risk management of Salmonella spp. along the food chain, including during product storage and distribution.

SUBMITTER: Kang MS

PROVIDER: S-EPMC7996612 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Predictive Modeling for the Growth of Salmonella spp. in Liquid Egg White and Application of Scenario-Based Risk Estimation.

Kang Mi Seon MS Park Jin Hwa JH Kim Hyun Jung HJ

Microorganisms 20210225 3

The objective of the study was to develop a predictive model of Salmonella spp. growth in pasteurized liquid egg white (LEW) and to estimate the salmonellosis risk using the baseline model and scenario analysis. Samples were inoculated with six strains of Salmonella, and bacterial growth was observed during storage at 10-37 °C. The primary models were developed using the Baranyi model for LEW. For the secondary models, the obtained specific growth rate (μmax) and lag pha ...[more]

PMID: 33669000

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Project description:Salmonella enterica serovar Enteritidis is noted for its ability to survive the harsh antibacterial activity of egg white which is presumed to explain its occurrence as the major food-borne pathogen associated with the consumption of eggs and egg products. Liquid egg white is a major ingredient for the food industry but, because of its thermal fragility, pasteurization is performed at the modest temperature of 57°C (for 2-6 min). Unfortunately, such treatment does not lead to sufficient reduction in S. Enteritidis contamination, which is a clear health concern when the product is consumed without cooking. However, egg white is able to limit S. Enteritidis growth due to its alkaline pH, iron deficiency and multiple antimicrobial proteins. This anti-Salmonella activity of egg white is temperature dependent and becomes bactericidal once the incubation temperature exceeds 42°C. This property is exploited in the highly promising pasteurization treatment (42-45°C for 1-5 days) which achieves complete killing of S. Enteritidis. However, the precise mechanism and the role of the egg-white proteins are not fully understood. Here, the impact of exposure of S. Enteritidis to egg white-based media, with or without egg-white proteins (>10 kDa), under bactericidal conditions (45°C) was explored by measuring survival and global expression. Surprisingly, the bactericidal activity of egg white at 45°C was only slightly affected by egg-white proteins indicating that they play a minor role in the bactericidal activity observed. Moreover, egg-white proteins had minimal impact on the global-gene-expression response to egg white such that very similar, major regulatory responses (20% genes affected) were observed both with and without egg-white proteins following incubation for 45 min at 45°C. Egg-white proteins caused a significant change in expression for just 64 genes, including the psp and lysozyme-inhibitor responses genes which is suggestive of an early membrane perturbation effect. Such damage was supported by disruption of the proton motive force by egg-white proteins. In summary, the results suggest that low-mass components of egg white are largely responsible for the bactericidal activity of egg white at 45°C.

Project description:The survival mechanism of Salmonella enterica serovar Enteritidis in antibacterial egg white is not fully understood. In our lab, an egg white-resistant strain, S. Enteritidis SJTUF 10978, was identified. Cell envelope damage and osmotic stress response (separation of cell wall and inner membrane as well as cytoplasmic shrinkage) of this strain surviving in egg white were identified through microscopic observation. RNA-Seq analysis of the transcriptome of Salmonella survival in egg white showed that a considerable number of genes involved in DNA damage repair, alkaline pH adaptation, osmotic stress adaptation, envelope damage repair, Salmonella pathogenicity island 2 (SPI-2), iron absorption, and biotin synthesis were significantly upregulated (fold change ≥ 2) in egg white, indicating that these pathways or genes might be critical for bacterial survival. RNA-Seq results were confirmed by qRT-PCR, and the survival analysis of six gene deletion mutants confirmed their importance in the survival of bacteria in egg white. The importance of alkaline pH adaptation and envelope damage repair for Salmonella to survive in egg white were further confirmed by analysis of nhaA, cpxR, waaH, and eco deletion mutants. According to the RNA-Seq results, we propose that alkaline pH adaptation might be the cause of bacterial osmotic stress phenotype and that the synergistic effect between alkaline pH and other inhibitory factors can enhance the bacteriostatic effect of egg white. Moreover, cpxR and sigE were recognized as the central regulators that coordinate bacterial metabolism to adapt to envelope damage and alkaline pH.IMPORTANCESalmonella enterica serovar Enteritidis is a major foodborne pathogen that causes salmonellosis mainly through contaminated chicken eggs or egg products and has been a worldwide public health threat since 1980. Frequent outbreaks of this serotype through eggs correlate significantly with its exceptional survival ability in the antibacterial egg white. Research on the survival mechanism of S. Enteritidis in egg white will help to further understand the complex and highly effective antibacterial mechanisms of egg white and lay the foundation for the development of safe and effective vaccines to prevent egg contamination by this Salmonella serotype. Key pathways and genes that were previously overlooked under bactericidal conditions were characterized as being induced in egg white, and synergistic effects between different antimicrobial factors appear to exist according to the gene expression changes. Our work provides new insights into the survival mechanism of S. Enteritidis in egg white.

Project description:Purpose: To elucidated key metabolic pathways important for S. Enteritidis survival in egg white. Methods: RNA sample of Mid-log phase bacteria cultures that grown in M9FeS medium were taken as 0h sample, and bacteria incubated with egg white for 6h 12h and 24h were taken as 6,12,24h RNA sample respectively. Three biological replicates were carried out per sample. RNA sample was sequenced with Illumina HiSeq 2000 System. DESeq2 method was used to calculate the differentially expressed genes. qRT–PCR and gene mutation were used to validate RNA-seq result. Results: A total of 12 samples were sequenced. The average output of each sample was 1.33 Gb, and the average comparison rate with the reference genome was 97.51%. M9FeS and egg whites cultivation resulted in 2400 to 2700 expressed genes accounting for 53 to 58% of the whole genome. In this group, 1240 to 1470 genes had significant levels of log2 fold changes ≥1, (Padj <0.05) compared with control. These accounted for 27.3 to 32.2% of the whole genome indicating a large shift in the transcriptional response to egg whites. qRT–PCR result of 21 selected genes highly consistent with the RNAseq results at all three timepoints. 8 out of 12 DEGs mutants showed decreased survival ability in egg white, suggested that the DEGs from the RNAseq results correlated significantly with the egg white resistance phenotype. Conclusions: Using strand-specific RNA sequencing, we found pathways significantly changed in egg white. Genes involved in SOS-dependent and independent DNA damage repair, alkaline pH adaption, osmotic stress adaption, envelope damage repair including maintaining periplasm homeostasis and reinforcing peptidoglycan layer, nitrogen assimilation, Salmonella pathogenicity island 2, iron absorption and biotin synthesis, were significantly up regulated in bacteria surviving in egg whites. Differentially expressed genes involved in energy metabolism, translation, and cell motility, Salmonella pathogenicity island 1 were significantly down-regulated in egg whites.

Dataset Information

Predictive Modeling for the Growth of Salmonella spp. in Liquid Egg White and Application of Scenario-Based Risk Estimation.

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Predictive Modeling for the Growth of <i>Salmonella</i> spp. in Liquid Egg White and Application of Scenario-Based Risk Estimation.

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