A microbial challenge study for validating continuous radio-frequency assisted thermal processing pasteurization of egg white powder.

Spray dried egg white powder (EWP) is traditionally processed by hot room treatment for a prolonged period of time (67 °C for 15 days) to enhance its functionality (foaming and gelling) and to improve microbial safety of EWP. Our prior research demonstrated that radio-frequency (RF) assisted thermal processing can considerably reduce the processing time, without compromising the functional properties of EWP. In this study, continuous RF processing was evaluated for pasteurization of EWP. EWP samples were inoculated with a 5-strain Salmonella cocktail or Enterococcus faecium NRRL B-2354 for the microbial challenge studies. To evaluate the inoculation method, stability and homogeneity tests were conducted for both Salmonella and E. faecium in EWP. Continuous RF heating of EWP was conducted in a 6-kW, 27.12 MHz pilot-scale parallel-plate RF heating system. RF-assisted thermal processing of EWP at 80 °C for 2 h provided >6.69 log reduction for Salmonella. E. faecium was found to be a suitable surrogate for Salmonella due to its higher resistance and similar inactivation kinetics during RF heating of EWP. The validated RF-assisted thermal process can be scaled up for use in the egg industry.

Identification of the bacteria and their metabolic activities associated with the microbial spoilage of custard cream desserts.

The famous French dessert "ile flottante" consists of a sweet egg white foam floating on a vanilla custard cream, which contains highly nutritive raw materials, including milk, sugar and egg. Spoilage issues are therefore a key concern for the manufacturers. This study explored the bacterial diversity of 64 spoiled custard cream desserts manufactured by 2 French companies. B. cereus group bacteria, coagulase negative Staphylococcus, Enterococcus and Leuconostoc spp. were isolated from spoiled products. Thirty-one bacterial isolates representative of the main spoilage species were tested for their spoilage abilities. Significant growth and pH decrease were observed regardless of species. While off-odours were detected with B. cereus group and staphylococci, yoghurt odours were detected with Enterococcus spp. and Leuconostoc spp. B. cereus group bacteria produced various esters and several compounds derived from amino acid and sugar metabolism. Most Staphylococci produced phenolic compounds. Enterococcus spp. and Leuconostoc spp. isolates produced high levels of compounds derived from sugar metabolism. Each type of spoilage bacteria was associated with a specific volatile profile and lactic acid was identified as a potential marker of spoilage of custard cream-based desserts. These findings provide valuable information for manufacturers to improve food spoilage detection and prevention of chilled desserts made with milk and egg.

The anti-bacterial iron-restriction defence mechanisms of egg white; the potential role of three lipocalin-like proteins in resistance against Salmonella.

Salmonella enterica serovar Enteritidis (SE) is the most frequently-detected Salmonella in foodborne outbreaks in the European Union. Among such outbreaks, egg and egg products were identified as the most common vehicles of infection. Possibly, the major antibacterial property of egg white is iron restriction, which results from the presence of the iron-binding protein, ovotransferrin. To circumvent iron restriction, SE synthesise catecholate siderophores (i.e. enterobactin and salmochelin) that can chelate iron from host iron-binding proteins. Here, we highlight the role of lipocalin-like proteins found in egg white that could enhance egg-white iron restriction through sequestration of certain siderophores, including enterobactin. Indeed, it is now apparent that the egg-white lipocalin, Ex-FABP, can inhibit bacterial growth via its siderophore-binding capacity in vitro. However, it remains unclear whether Ex-FABP performs such a function in egg white or during bird infection. Regarding the two other lipocalins of egg white (Cal-γ and α-1-glycoprotein), there is currently no evidence to indicate that they sequester siderophores.

Salmonella Typhimurium is Attracted to Egg Yolk and Repelled by Albumen.

Salmonella Typhimurium is the causative agent of non-typhoidal, foodborne salmonellosis. Contamination of hen eggs by the bacterium is a common source of S. Typhimurium infection. S. Typhimurium is peritrichous, and flagellum-dependent motility and chemotaxis are believed to facilitate egg contamination despite the presence of many antimicrobial egg components. We performed motility and chemotaxis assays to demonstrate that S. Typhimurium cells are attracted to egg yolks and are repelled by albumen. The bacterial flagellar motor shows bidirectional rotation, and counterclockwise-biased rotation allows cells to swim smoothly. A rotation assay for a single flagellum showed that, in comparison with thin albumen, the thick albumen more strongly affected the directional bias of the flagellar rotation, resulting in a remarkable suppression of the migration distance. Nevertheless, the S. Typhimurium cells retained positive chemotaxis toward the yolk in the presence of the albumens, suggesting that motility facilitates the growth of S. Typhimurium and survival in eggs.

Egg white versus Salmonella Enteritidis! A harsh medium meets a resilient pathogen.

Salmonella enterica serovar Enteritidis is the prevalent egg-product-related food-borne pathogen. The egg-contamination capacity of S. Enteritidis includes its exceptional survival capability within the harsh conditions provided by egg white. Egg white proteins, such as lysozyme and ovotransferrin, are well known to play important roles in defence against bacterial invaders. Indeed, several additional minor proteins and peptides have recently been found to play known or potential roles in protection against bacterial contamination. However, although such antibacterial proteins are well studied, little is known about their efficacy under the environmental conditions prevalent in egg white. Thus, the influence of factors such as temperature, alkalinity, nutrient restriction, viscosity and cooperative interactions on the activities of antibacterial proteins in egg white remains unclear. This review critically assesses the available evidence on the antimicrobial components of egg white. In addition, mechanisms employed by S. Enteritidis to resist egg white exposure are also considered along with various genetic studies that have shed light upon egg white resistance systems. We also consider how multiple, antibacterial proteins operate in association with specific environmental factors within egg white to generate a lethal protective cocktail that preserves sterility.

A genome-wide screen identifies Salmonella Enteritidis lipopolysaccharide biosynthesis and the HtrA heat shock protein as crucial factors involved in egg white persistence at chicken body temperature.

Eggs contaminated with Salmonella Enteritidis are an important source of human foodborne Salmonella infections. Salmonella Enteritidis is able to contaminate egg white during formation of the egg within the chicken oviduct, and it has developed strategies to withstand the antimicrobial properties of egg white to survive in this hostile environment. The mechanisms involved in the persistence of Salmonella Enteritidis in egg white are likely to be complex. To address this issue, a microarray-based transposon library screen was performed to identify genes necessary for survival of Salmonella Enteritidis in egg white at chicken body temperature. The majority of identified genes belonged to the lipopolysaccharide biosynthesis pathway. Additionally, we provide evidence that the serine protease/heat shock protein (HtrA) appears essential for the survival of Salmonella Enteritidis in egg white at chicken body temperature.

Salmonella Enteritidis is superior in egg white survival compared with other Salmonella serotypes.

Salmonella enterica subspecies enterica serotype Enteritidis is a major cause of egg-borne human salmonellosis. The ability to survive in egg albumen at chicken body temperature was hypothesized to be an important factor involved in the predominant contamination of eggs by this specific serotype. Eighty-nine Salmonella strains from different serotypes, belonging to 5 serogroups, were incubated for 24 h in egg white at 42°C. The number of Salmonella Enteritidis strains that were able to survive in egg white was significantly higher compared with strains belonging to other serotypes and serogroups that were tested in this study. These data add evidence to the hypothesis that egg white survival is one of the reasons why Salmonella Enteritidis is more predominantly isolated from contaminated eggs, and helps explaining why most reported egg-borne Salmonella outbreaks in humans are caused by Salmonella Enteritidis.

Salmonella Enteritidis strains from poultry exhibit differential responses to acid stress, oxidative stress, and survival in the egg albumen.

Salmonella Enteritidis is the major foodborne pathogen that is primarily transmitted by contaminated chicken meat and eggs. We recently demonstrated that Salmonella Enteritidis strains from poultry differ in their ability to invade human intestinal cells and cause disease in orally challenged mice. Here we hypothesized that the differential virulence of Salmonella Enteritidis strains is due to the differential fitness in the adverse environments that may be encountered during infection in the host. The responses of a panel of six Salmonella Enteritidis strains to acid stress, oxidative stress, survival in egg albumen, and the ability to cause infection in chickens were analyzed. This analysis allowed classification of strains into two categories, stress-sensitive and stress-resistant, with the former showing significantly (p<0.05) reduced survival in acidic (gastric phase of infection) and oxidative (intestinal and systemic phase of infection) stress. Stress-sensitive strains also showed impaired intestinal colonization and systemic dissemination in orally inoculated chickens and failed to survive/grow in egg albumen. Comparative genomic hybridization microarray analysis revealed no differences at the discriminatory level of the whole gene content between stress-sensitive and stress-resistant strains. However, sequencing of rpoS, a stress-regulatory gene, revealed that one of the three stress-sensitive strains carried an insertion mutation in the rpoS resulting in truncation of σ(S). Finding that one of the stress-sensitive strains carried an easily identifiable small polymorphism within a stress-response gene suggests that the other strains may also have small polymorphisms elsewhere in the genome, which likely impact regulation of stress or virulence associated genes in some manner.

Inactivation of Salmonella in liquid egg albumen by antimicrobial bottle coatings infused with allyl isothiocyanate, nisin and zinc oxide nanoparticles.

AIMS: To develop an antimicrobial bottle coating effective at inhibiting the growth of Salmonella in liquid egg albumen (egg white) and reduce the risk of human Salmonellosis. METHODS AND RESULTS: Four-ounce glass jars were coated with a mixture of polylactic acid (PLA) polymer and antimicrobial compounds containing 100-500 µl allyl isothiocyanate (AIT), 250 mg nisin, 250 mg zinc oxide nanoparticles per jar or their combinations. The coated jars contained 100 ml of liquid egg white (LEW) inoculated with a three-strain Salmonella enterica ssp. enterica cocktail at populations of 10(3) or 10(7) CFU ml(-1) and stored at 10°C for 28 days. The PLA coating with 500 µl AIT completely inactivated 3 and 7 log CFU ml(-1) of Salmonella after 7 and 21 days of storage, respectively. The PLA coating with 200 µl AIT in combination with 250 mg nisin reduced Salmonella populations to an undetectable level (<10 CFU ml(-1) ) after 21 days of storage. CONCLUSIONS: PLA coatings containing AIT alone or in combination with nisin effectively inactivated salmonellae in LEW. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated the commercial potential of applying the antimicrobial bottle coating method to liquid eggs and possibly other fluid food products.

Lysozyme as a barrier to growth of Bacillus anthracis strain Sterne in liquid egg white, milk and beef.

In this study, we investigated the role of lysozyme on the viability of Bacillus cereus, Bacillus subtilis, Bacillus pumilus and Bacillus anthracis (Sterne) in egg white (EW), ground beef and milk. At 35 °C in EW, growth rates (GR) for B. cereus, B. subtilis, B. pumilus and B. anthracis were 0.005, -0.018, -0.028 and -0.029 OD(600)/h, respectively. Heat-treating EW at 55 and 60 °C reduced the inactivating effect of EW by 3.1 and 10.5-fold, respectively. Addition of lysozyme (2 mg/ml) to 60 °C-treated EW increased the inactivation rate 5.76-fold, indicating involvement of lysozyme in B. anthracis inactivation. B. anthracis inactivation was influenced by pH, as shown by a progressive increase in inactivation rate from 0.25 to -4.42 logs CFU/h over a pH range of 6.0-8.5. Adding 2 mg/ml lysozyme to milk and ground beef also suppressed the growth of B. anthracis 3.3 and 6.5-fold, respectively. These data indicate that lysozyme, as a natural component of EW or potential additive in other foods, could reduce biothreat risks presented by bioterror agents.

Influence of carbon dioxide on the activity of chicken egg white lysozyme.

Rapid cooling of shell eggs by using liquid CO(2) has shown increased bactericidal effects along with saturation of the egg albumen with CO(2). Lysozyme is a bactericidal enzyme present in chicken eggs, and it lyses gram-positive bacteria. Newly laid chicken eggs have an initial pH of 7.6 to 8.5 and are saturated with CO(2). During storage, the pH gradually increases to 9.7, accompanied by a loss of CO(2). It is hypothesized that the lysozyme activity is influenced by either CO(2) concentration or pH changes resulting from CO(2) loss. The objective of this study was to determine the lytic activity of purified lysozyme and chicken egg white (unpurified lysozyme) under varying conditions of temperature, pH, and CO(2) gas concentration. Lytic activity was determined by a standard microbial assay using lyophilized Micrococcus lysodeikticus. A 2 × 4 × 2 × 2 × 3 factorial design consisting of 2 temperatures (5 and 22°C), 4 pH (4.5, 6.5, 8.0, and 9.5), 2 treatments (with and without CO(2)), 2 types of lysozyme (purified and unpurified egg white), and 3 replicates was used. The highest lytic activity was found at pH 6.5 and 22°C. At pH 4.5 and 8.0, the addition of CO(2) increased lytic activity by more than 50% at both temperatures. At pH 6.5, lytic activity was maintained with CO(2) addition at both temperatures. At pH 9.5, lytic activity without CO(2) addition was high; however, adding CO(2) reduced lytic activity to zero. In conclusion, both pH and CO(2) treatment influence lysozyme activity.

Specific gene SEN1393 contributes to higher survivability of Salmonella Enteritidis in egg white by regulating sulfate assimilation pathway.

Salmonella enterica serovar Enteritidis (S. Enteritidis) presents an excellent capacity to survive in egg white, which is a hostile environment for bacterial growth. To reveal its survival mechanism, this study focuses on the specific gene SEN1393, which has been found to exist only in the genomic sequence of S. Enteritidis. The survival capacity of the deletion mutant strain ΔSEN1393 was proven to be significantly reduced after incubation in egg white. RNA sequencing and RT-qPCR results demonstrate that the expression levels of 19 genes were up-regulated, while the expression levels of 9 genes were down-regulated in egg white. These genes were classified into 6 groups based on their functional categories, namely the sulfate assimilation pathway, arginine biosynthesis, the tricarboxylic acid cycle, the fimbrial protein, the transport and chelation of metal ion, and others (sctT, rhs, and pspG). The strain ΔSEN1393 was deduced to damage FeS cluster enzymes and increase the sulfate and iron requirements, and to reduce bacterial motility and copper homeostasis. Via InterProScan analysis, the gene SEN1393 was speculated to encode a TerB-like and/or DjlA-like protein, and therefore, together with cysJ, possibly reduced the oxidative toxicities resulting from oxyanions such as tellurite, and/or improved CysPUWA conformation to restrain the uptake of the toxic oxyanions. In summary, the gene SEN1393 enabled the higher survival of S. Enteritidis in egg white as compared to other pathogens by regulating the sulfate assimilation pathway.

Effect of temperature and time of storage on protein stability and anti-salmonella activity of egg white.

Hen egg white contains numerous molecules of interest for human health, including antimicrobial proteins. Little information is available concerning changes in the antimicrobial activity of egg white during storage; therefore, we analyzed the potential of egg white to inhibit growth of Salmonella enterica serovar Enteritidis following storage at 4, 20, or 37°C for 30 days prior to inoculation. Egg white displayed higher anti-Salmonella activity after a few days of storage at 20 and 37°C. The rate of increase in activity was more rapid and pronounced at the higher temperature. However, egg white stored at 20°C retained higher antimicrobial activity than that of egg white stored at 4 or 37°C, when the entire storage period is taken in consideration. In contrast, storage of egg at 37°C for more than 14 days reduced the bacteriostatic potential of egg white. Statistical analyses revealed a correlation between pH and the antimicrobial activity of egg white. Moreover, diminished antimicrobial activity was associated with degradation of ovalbumin and ovotransferrin, as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry. However, the fluctuation in anti-Salmonella activity of egg white could not be related to any variation of trypsin-like, chymotrypsin-like, or gelatinolytic activities that potentially account for degradation of antimicrobial egg white proteins.

Kinetics of growth and inactivation of Salmonella enterica serotype Typhimurium DT104 in pasteurised liquid egg products.

The potential impact of post-pasteurisation contamination of liquid egg products with the multi-antibiotic resistant pathogen Salmonella enterica serotype Typhimurium definitive type 104 (DT104) was assessed by determining the viability of this bacterium in whole egg, albumen and 10% w/w sugared and salted yolk incubated at 4-42 degrees C. Results indicated that populations of S. Typhimurium DT104 were slowly inactivated in all four products when stored at 4 degrees C. However, based on the typical shelf-lives of cold-stored liquid egg, less than 0.6 log-kill would be achieved in those products prior to their use. Incubation at temperatures pertaining to abuse situations (10, 15, 20 and 25 degrees C) revealed an increasing potential for growth of S. Typhimurium DT104 in whole egg, albumen and sugared yolk, as indicated by trends in growth rate, lag duration and maximum population density. At even higher temperatures (30, 37 and 42 degrees C), growth rates of S. Typhimurium DT104 in whole egg and sugared yolk continued to increase. The same was true for S. Typhimurium DT104 in albumen except that growth was not observed at 42 degrees C and instead populations were inactivated within 30 h. At no temperature tested was S. Typhimurium DT104 able to grow in salted yolk. The influence of these growth and inactivation patterns on the risk of salmonellosis in relation to product type and storage temperature is discussed.

Ergosterol as an indicator of the presence of microscopic fungi in eggs for human consumption produced in different husbandry systems.

Ergosterol (ERG) content, being an indicator of fungal biomass, was analyzed in samples of eggshell, egg white, and egg yolk from eggs from farms with intensive management systems of layer hens (i.e., cage and litter housing). Moreover, analogous samples were analyzed from eggs from farms in the western central part of Poland, where layer hens were kept in the organic system. In all samples, the highest ERG concentration was found in shells and the lowest in egg white, whereas ERG was not found in egg yolk. When comparing investigated housing systems, a higher concentration of the analyzed metabolite was detected in eggs from litter housing than in eggs from cage housing. Concentrations of ERG in samples of eggs from organic husbandry were highly varied, ranging from 2.44 to 42.67 mg/kg in shells and from 0.28 to 16.11 mg/kg in egg white.

Inactivation of Escherichia coli K-12 in Liquid Egg White By a Flow-through Pulsed Uv Light Treatment System.

ABSTRACT: Unpasteurized liquid egg can be contaminated with pathogenic microorganisms and may cause foodborne outbreaks. Thus, it is essential to decontaminate the liquid egg to ensure food safety. Pulsed UV light is one of the emerging technologies for food decontamination in recent years. This static treatment system has been studied previously in our laboratory. However, continuous processing using a flow-through treatment system needs to be evaluated for potential commercial applications. Therefore, in this study, a flow-through treatment system of pulsed UV light was evaluated and optimized for inactivation of Escherichia coli K12NSR for liquid egg white decontamination. Treatment factors including flow rate (40 to 80 mL/min), number of passes (one to three passes), and distance from the sample to the pulsed UV light strobe (5 to 13 cm) were optimized using response surface methodology. This methodology suggested three passes with 40 mL/min flow rate and a 5-cm distance as the optimum conditions. The model was then validated for the maximum reduction of E. coli K12NSR, which was measured as 1.57 log CFU/mL at the optimal conditions. The energy doses of the pulsed UV light and temperature changes of the liquid egg white during the treatment were measured. Furthermore, several quality parameters were assessed at the optimum treatment conditions to determine the impact of the flow-through pulsed UV processing on the quality of liquid egg white. The results showed significant differences in pH, lipid oxidation, turbidity, and color between control and pulsed UV light-treated samples (P < 0.05). However, there was no significant difference in foaming ability or foam stability between pulsed UV light-treated samples and the control. Overall, this study demonstrated the potential of flow-through pulsed UV light to decontaminate liquid egg white, but further research is needed for optimal enhancement.

Role of yoaE Gene Regulated by CpxR in the Survival of Salmonella enterica Serovar Enteritidis in Antibacterial Egg White.

The survival ability of Salmonella enterica serovar Enteritidis in antibacterial egg white is an important factor leading to Salmonella outbreaks through eggs and egg products. In this study, the role of the gene yoaE, encoding an inner membrane protein, in the survival of Salmonella Enteritidis in egg white, and its transcriptional regulation by CpxR were investigated. Quantitative reverse transcription-PCR (RT-qPCR) results showed that the yoaE gene expression was upregulated 35-fold after exposure to egg white for 4 h compared to that in M9FeS medium, and the deletion of yoaE (ΔyoaE) dramatically decreased the survival rate of bacteria in egg white to less than 1% of the wild type (WT) and the complementary strain at both 37 and 20°C, indicating that yoaE was essential for bacteria to survive in egg white. Furthermore, the ΔyoaE strain was sensitive to a 3-kDa ultrafiltration matrix of egg white because of its high pH and antimicrobial peptide components. Putative conserved binding sites for the envelope stress response regulator CpxR were found in the yoaE promoter region. In vivo, the RT-qPCR assay results showed that the upregulation of yoaE in a ΔcpxR strain in egg white was 1/5 that of the WT. In vitro, results from DNase I footprinting and electrophoretic mobility shift assays further demonstrated that CpxR could directly bind to the yoaE promoter region, and a specific CpxR binding sequence was identified. In conclusion, it was shown for the first time that CpxR positively regulated the transcription of yoaE, which was indispensable for survival of Salmonella Enteritidis in egg white.IMPORTANCESalmonella enterica serovar Enteritidis is the predominant Salmonella serotype that causes human salmonellosis mainly through contaminated chicken eggs or egg products and has been a global public health threat. The spread and frequent outbreaks of this serotype through eggs correlate significantly with its exceptional survival in eggs, despite the antibacterial properties of egg white. Research on the survival mechanisms of S. Enteritidis in egg white will help develop effective strategies to control the contamination of eggs by this Salmonella serotype and help further elucidate the complex antibacterial mechanisms of egg white. This study revealed the importance of yoaE, a gene with unknown function, on the survival of S. Enteritidis in egg white, as well as its transcriptional regulation by CpxR. Our work provides the basis to reveal the mechanisms of survival of S. Enteritidis in egg white and the specific function of the yoaE gene.

Duan-Nai-An, A Yeast Probiotic, Improves Intestinal Mucosa Integrity and Immune Function in Weaned Piglets.

Post-weaning diarrhea commonly occurs in piglets and results in significant economic loss to swine producers. Non-antibiotic measures for managing post-weaning diarrhea are critically needed. Duan-Nai-An, a probiotic produced from the yeast fermentation of egg whites, was previously shown to optimize intestinal flora and reduce the incidence of clinical diarrhea in weaning piglets. To study the effects of Duan-Nai-An on mucosal integrity and immunity in pig intestine, we examined the microstructure and ultrastructure of the intestines of weaned pigs with or without Duan-Nai-An as a feed supplement. The piglets of the Duan-Nai-An-fed group developed intestines with intact columnar epithelia covered by tightly packed microvilli on the apical surface. However, piglets of the control group (no supplement) showed villous atrophy and thinning, microvillus slough, and in the severe cases, damage of intestinal epithelia and exposure of the underlying lamina propria. Moreover, piglets of the Duan-Nai-An-fed group showed apparent plasmocyte hyperplasia, increased lymphoid nodule numbers, well-developed Peyer's Patchs, and apparent germinal centers. The lymphoid tissues of the control group were far less developed, showing lymph node atrophy, lymphocyte reduction, degeneration, and necrosis. These results indicate that Duan-Nai-An improves the development of the intestinal structures and lymphoid tissues and promotes intestinal health in weaned piglets.

Development of a macrophage cell culture method to isolate and enrich Francisella tularensis from food matrices for subsequent detection by real-time PCR.

Francisella tularensis is a gram-negative bacterium that can cause gastrointestinal or oropharyngeal tularemia in humans from ingestion of contaminated food or water. Despite the potential for accidental or intentional contamination of foods with F. tularensis, there are no techniques currently available to detect this organism in specific food matrices. In this study, a macrophage cell culture system is combined with real-time PCR to identify F. tularensis in food matrices. The method utilizes a mouse macrophage cell line (RAW 264.7) as host for the isolation and intracellular replication of F. tularensis. Exposure of macrophages to F. tularensis-contaminated food matrices results in uptake and intracellular replication of the bacteria, which can be subsequently detected by real-time PCR analysis of the DNA released from infected macrophage cell lysates. Macrophage monolayers were exposed to infant formula, liquid egg whites, and lettuce contaminated with varying quantities of F. tularensis. As few as 10 CFU/ml (or CFU per gram) F. tularensis was detected in infant formula and lettuce after 5 h postinfection. As few as 10 CFU/ml F. tularensis was detected in liquid egg whites after 18 h postinfection. Intracellular F. tularensis could also be isolated on Mueller-Hinton medium from lysates of macrophages infected with the bacteria in infant formula, liquid egg whites, and lettuce for subsequent confirmatory identification. This method is the first to successfully identify F. tularensis from select food matrices.

Comparison of supplements to enhance recovery of heat-injured Salmonella from egg albumen.

AIMS: The purpose of this study was to determine the proficiency of supplements to enhance the recovery of Salmonella from heat-treated liquid egg albumen on solid agar media. METHODS AND RESULTS: Salmonella-inoculated albumen, heated at 53.3 degrees C for 4 min, was plated on 39 combinations of solid media with or without the addition of 12 supplements. Greater numbers of Salmonella (P < 0.05) recovered with the addition of 1.0 g l(-1) ferrous sulfate (FeSO(4)) than with any other supplements, except for 0.5 or 1.0 g l(-1) 3'3'-thiodipropionic acid (TDP), which recovered equivalent populations. Addition of 1.0 g l(-1) sodium pyruvate or 6.0 g l(-1) yeast extract plus 1.0 g l(-1) sodium pyruvate supported greater resuscitation than unsupplemented tryptic soy agar (TSA) or supplementing with 0.01 or 0.1 g l(-1) N-propyl gallate, 10 g l(-1) activated charcoal, 0.1 g l(-1) KMnO(4) or 50 mg l(-1) ethoxyquin. The remaining supplements supported recovery of equivalent numbers of Salmonella, which were fewer cells than recovered with 1.0 g l(-1) FeSO(4), yet greater populations than recovered with 50 mg l(-1) ethoxyquin. CONCLUSION: Supplementation of plating media with FeSO(4), TDP or sodium pyruvate enhanced recovery of sublethally injured Salmonella from albumen. SIGNIFICANCE AND IMPACT OF THE STUDY: Pasteurizing albumen impedes recovery of pathogens. These results suggest that the addition of supplements to plating media may assist resuscitation and colony development of heat-injured salmonellae.