Outgrowth of Salmonellae and the physical property of albumen and vitelline membrane as influenced by egg storage conditions

This study was undertaken to determine the influence of storage time and temperature on the volume, weight, and pH of egg albumen, the physical strength of vitelline membrane, and the fate of Salmonella Enteritidis artificially inoculated into egg albumen. A fiber-optic probe was used for inoculation with Salmonella Enteritidis at 10(2), 10(4), or 10(6) cells per egg. Both fresh and inoculated eggs were stored at 4, 10, and 22 degrees C for 6 weeks. Five fresh uninoculated eggs from each storage group were collected each week, and the weight, volume, and pH of the egg albumen were measured. The forces, energies, and degrees of membrane deformation required to rupture the vitelline membranes also were determined from either albumen-free yolks or yolks surrounded by albumen. In separate experiments, five inoculated eggs were evaluated each week for populations of Salmonella Enteritidis. When the eggs were stored at 4 degrees C, the albumen retained significantly more volume and weight and had a relatively lower pH. The vitelline membranes from eggs stored at 4 and 10 degrees C required more force and energy for rupture. Salmonellae flourished at 22 degrees C, even in the albumen with the lowest initial population, 10(2) cells per egg. Storage at 4 and 10 degrees C inhibited the growth of salmonellae in the albumen of eggs with initial populations of 10(2), 10(4), or 10(6) cells per egg. In eggs with initial Salmonella populations of 10(6) cells per egg that were stored at 22 degrees C, the populations of reached as high as 10(10) cells per egg after 4 weeks of storage. Storage at 4 and perhaps 10 degrees C postponed the aging process of chicken eggs, preserved the antimicrobial agents of the albumen, and maintained the integrity of vitelline membrane. Low-temperature storage therefore had a significant impact on the safety and overall quality of the eggs.     

Populations of Salmonella enteritidis in artificially inoculated chicken eggs as influenced by the temperatures under which eggs might be held from the day of lay until the day of processing

This study was undertaken to determine the levels of Salmonella Enteritidis in artificially inoculated eggs as affected by the temperatures under which eggs might be held from the day of lay until the day of processing. Unprocessed chicken eggs of different sizes (n=1920, with 480 being laid in each season) were inoculated in the albumen with a five-strain mixture of Salmonella at 102 CFU per egg. The eggs were stored at 4, 10, and 22 degrees C for 3 weeks and sampled twice a week to determine the populations of Salmonella and total aerobic bacteria. The season in which eggs were laid did not significantly impact the growth of the pathogen (P > 0.05). The mean populations of the inoculated Salmonella were not significantly different in eggs stored at 4 versus 10 degrees C (P > 0.05). Eggs stored at 22 degrees C had a mean Salmonella population that was 3.71 or 3.37 log higher than the Salmonella population of eggs stored at 4 or 10 degrees C (P > 0.05). The mean Salmonella population at 22 degrees C increased from the initial 2.12 log CFU/ml to 3.36 log CFU/ml after 2 weeks of storage and to 7.84 log CFU/ml after 3 weeks of storage. A sharp increase in the population of Salmonella occurred after 2 to 2.5 weeks of storage at 22 degree C. This study provided a scientific basis for the current egg handling and transporting temperature requirements and reinforced the importance of maintaining low temperatures in controlling and preventing the growth of Salmonella Enteritidis in eggs from the day of lay until the day of processing.     

Multiplication and motility of Salmonella enterica serovars enteritidis, infantis, and montevideo in in vitro contamination models of eggs

The invasive ability of Salmonella enterica serovars Enteritidis, Infantis, and Montevideo in eggs was examined. Strains of these serovars originating from egg contents, laying chicken houses, and human patients were experimentally inoculated (0.1-ml dose containing 78 to 178 cells) onto the vitelline membrane of eggs collected from specific-pathogen-free chickens and incubated at 25 degrees C. The test strains were detected in 25 of 138 yolk contents by day 6, indicating the penetration of Salmonella organisms through the vitelline membrane. There were no significant differences in overall rates of penetration between serovars. The organisms were also detected in the albumen from 125 of 138 eggs tested by day 6. Growth to more than 10(6) CFU/ml was observed in 48 of the 125 albumen samples. An inoculum of 1000 Salmonella cells was added to 15 ml of albumen at the edge of a petri plate. A 10-mm-diameter cylindrical well, the bottom of which was sealed with a polycarbonate membrane with 3.0-microm pores, was filled with egg yolk and placed into the albumen at the center of the dish, which was maintained at 25 degrees C. Experiments were performed in triplicate with each strain. Salmonella organisms in all the albumen samples were detected by day 11. However, motility of the organisms toward the yolk was observed in only two dishes inoculated with the Salmonella Enteritidis strain from a human patient and in one dish inoculated with the Salmonella Infantis strain from liquid egg. The albumen samples obtained from the dishes inoculated with the Salmonella Enteritidis strain had high numbers of bacteria (>10(8) CFU/ml). The present study suggests that Salmonella organisms in egg albumen are unlikely to actively move toward the yolk, although depositionon or near the vitelline membrane can be advantageous for proliferation.     

Laying season and egg shell cracks on the growth of Salmonella enteritidis in the egg albumen during storage

We studied the effects of laying seasons and egg shell cracks on the ability of egg albumen to support the growth of Salmonella Enteritidis (SE) in eggs. Hens eggs used were those laid in February, June, and October in a farm in Japan and stored at 10, 20, and 30 degrees C, and at 30 degrees C after storage at 10 degrees C, immediately after receipt or after cracking the shell. At several-day intervals during storage, the egg contents were poured into a dish, SE was inoculated into albumen, and then the growth of SE during 3 days incubation at 18 degrees C was measured. The results demonstrated that storage temperature and laying season affected the growth of SE in the egg albumen. The proportion of eggs upon which albumen allowed the growth of SE was higher in the eggs stored at 30 degrees C than those stored at 10 degrees C. The growth of SE in eggs was lowest in the following order of laying: February, October, and June. SE grew preferably in albumen of cracked eggs than intact eggs.     

EFFECT OF RAPID COOLING ON THE GROWTH AND PENETRATION OF SALMONELLA ENTERITIDIS INTO EGG CONTENTS

Shell eggs were inoculated internally with approximately 10 cells of Salmonella enterica serovar enteritidis (S. enteritidis) and subjected to three different cooling treatments. Eggs were cooled from an initial temperature of 27C to approximately 7.2C. After cooling, eggs were stored at approximately 7.2C for 36 days, or stored at 5.7–9.5C for 30 days plus 6 days at 37C to simulate temperature abuse. Rapid cooling and subsequent storage of eggs at approximately 7.2C inhibited the growth of S. enteritidis in eggs. Slow cooling, and/or temperature abuse promoted growth of S. enteritidis in eggs. The penetration study indicated that rapid cooling and subsequent storage at 7.2C for 30 days did not affect the penetration of S. enteritidis into egg contents. The S. enteritidis isolated from the eggshell with shell membranes was significantly higher (P < 0.05) than from the internal egg contents, indicating that most of the S. enteritidis cells were trapped within the shell pores and/or shell membranes.     

Growth of Salmonella serovars in hens’ egg albumen as affected by storage prior to inoculation

Different Salmonella enterica serovars, including Enteritidis, were tested for growth at 20°C in separated albumen upon inoculation with 39 cfu ml⁻¹. The albumen was fresh or stored for up to 3 weeks prior to inoculation (p.i.) either in the shell egg or separated from the yolk. The serovar Enteritidis did not behave differently than the other serovars indicating that the association between human S. Enteritidis infections and eggs is not due to its growth behaviour in albumen. A pronounced growth occurred more frequently and up to a one-log unit higher level in fresh albumen than in albumen stored p.i. This was at least partly explained by a pH effect. Since growth in the separated albumen was similar when the albumen had been stored p.i. in the absence or presence of yolk, we have no indication that nutrients or factors negating the inhibitory properties of the albumen leak out from the yolk during storage. Growth of Salmonella inoculated at a level of 8 cfu in the albumen of fresh and stored whole shell eggs was studied to simulate a more natural situation. In this case, growth also occurred more frequently when inoculated in the albumen of fresh eggs compared to eggs stored p.i. It can be concluded from our study that cooling practices are recommended shortly after lay to prevent Salmonella from growing in eggs.     

Growth of Salmonella enterica serovar Enteritidis in albumen and yolk contents of eggs inoculated with this organism onto the vitelline membrane

By using an in vitro model simulating the potential opportunities for Salmonella enterica serovar Enteritidis (SE) to proliferate within eggs contaminated with this organism following oviposition, we investigated growth of SE in eggs. Seventy to 140 CFU of one of three SE strains originating either from egg contents, chicken meat, or a human infection were experimentally inoculated onto the vitelline membrane of eggs collected from specific-pathogen-free flocks of chickens and incubated at 25 degrees C. SE organisms were detected in 6 of 71 yolk contents of the eggs inoculated with any of the test strains attaining levels ranging from 2.0 x 10(2) to 4.2 x 10(8) CFU/ml by day 6. The organisms were also detected in the albumen from 38 of 55 eggs tested, growing to levels ranging from 1.0 x 10(2) to 4.3 x 10(8) CFU/ml by day 6 after inoculation. An additional three yolk contents and 15 albumen samples were culture positive for SE following enrichment. There was no correlation between the number of the organisms in the yolk contents and that in the albumen from each of the eggs. When 73 to 91 CFU of the egg strain were inoculated into samples of separated albumen obtained from eggs that were stored at 4 degrees C for 1 to 4 weeks or at 25 degrees C for 1 week, slight growth (3.0 x 10(2) to 7.4 x 10(3) CFU/ml) was found in only 3 of the 60 albumen samples by day 6 after inoculation, but the organisms were recovered from 52 samples following enrichment. The results suggest that the environment on or near the vitelline membrane can be conducive to SE proliferation over time.     

Comparison of homogenization methods for recovering Salmonella Enteritidis from eggs

For Salmonella Enteritidis (SE) detection, shell eggs have been homogenized with stomachers, with electric blenders, and by hand massaging. However, to date, there have been no published reports addressing whether the method of homogenization affects the recovery of SE from raw eggs. Three inoculum levels (10, 126, and 256 SE cells per pool of 10 eggs) were used to conduct three experiments. The 10-egg pools were homogenized by one of four homogenization methods--mechanical stomaching, electric blending, hand massaging, and hand stirring-for 30 s. The homogenized eggs were then incubated at 37 degrees C, and SE colonies were enumerated after 24 and 48 h of incubation. After 24 h of incubation, no SE was recovered from egg samples from stomached or electrically blended pools inoculated with <10 cells, while levels of 106 CFU/ml were found for samples from whipped or hand-massaged pools inoculated with <10 cells. Similarly, after 24 h of incubation, the numbers of SE cells recovered from hand-massaged or hand-stirred egg pools inoculated with 126 cells were significantly larger than the numbers recovered from stomached or electrically blended egg pools inoculated with 126 cells. The number of SE cells recovered from samples homogenized with a blender was still significantly smaller than the numbers recovered from samples homogenized by the other three methods when the inoculum level was increased to 256 CFU per pool. However, the SE count for all samples approached 9 log10 CFU/ml after 48 h of incubation. It is concluded that the detection of small SE populations in shell egg samples could be improved with the use hand massaging and hand stirring for homogenization.     

Detection of Salmonella enteritidis in shell and liquid eggs using enrichment and plating

Detection methods using various enrichment and plating media and immunoconcentration for Salmonella enteritidis in shell and liquid eggs were evaluated. For liquid egg samples naturally contaminated with S. enteritidis, pre-enrichment in 225 ml of buffered peptone water with cysteine followed by selective enrichment in 10 ml of tetrathionate broth was the superior, resulting in the detection of S. enteritidis in all samples on six of the seven types of selective agar substrate investigated. This enrichment procedure also enabled detection of S. enteritidis in most of artificially inoculated shell egg and pasteurized liquid egg samples.     

Growth of Salmonella enteritidis in yolk from eggs laid by immunized hens

After hyperimmunization of laying hens with Salmonella enteritidis, antibodies can be found in egg yolks. This study was conducted to ascertain whether the growth of S. enteritidis would be suppressed in the presence of antibodies contained in egg yolk. Specifically pathogen-free (SPF)-laying hens were immunized with S. enteritidis; eggs were collected, the yolk was separated and the concentration of S. enteritidis antibodies was determined quantitatively by using the enzyme-linked immunosorbent assay (ELISA), the radial immunodiffusion and the bicinchoninic acid protein assay. Then, the yolk was inoculated with approximately 10, 100 or 1000 S. enteritidis cells/ml and incubated at 15, 20 and 30 degrees C for 0, 2, 6 and 24 h. The growth of organisms in each yolk was examined, and the generation times were calculated. The egg yolk from nonimmunized hens served as negative control. The highest level of antibody concentration was found in the hyperimmunized group. There was no difference in the generation times of S. enteritidis between the antibody-positive yolk and the negative yolk at the three different incubation temperatures. The results suggest that antibodies in the yolk do not influence the growth of S. enteritidis, even if the hens are highly immunized.     

Survival of Salmonella enteritidis phage type 30 on inoculated almonds stored at -20, 4, 23, and 35 degrees C

To evaluate the survival of Salmonella on raw almond surfaces, whole almond kernels were inoculated with Salmonella Enteritidis phage type (PT) 30 collected from a 24-h broth culture or by scraping cells from an agar lawn. Kernels inoculated with lawn-collected cells to 8, 5, 3, and 1 log CFU per almond after a 24-h drying period were stored for 161 days at 23 +/- 3 degrees C. Calculated rates of reduction were similar for the four inoculum levels (0.22, 0.28, 0.29, and 0.22 log CFU/month, respectively). Kernels inoculated to 7.1 or 8.0 log CFU per almond after drying were stored for 171 or 550 days, respectively, at selected temperatures, including -20 +/- 2 degrees C, 4 +/- 2 degrees C, 23 +/- 3 degrees C, and 35 +/- 2 degrees C. No significant reductions of Salmonella were observed during storage at -20 and 4 degrees C over 550 days. At 35 degrees C, a biphasic survival curve was observed, with calculated reductions of 1.1 log CFU/month from days 0 to 59 and no significant reduction from days 59 to 171. At 23 degrees C, reductions of 0.18 and 0.30 log CFU/month were calculated for 171 and 550 days of storage, respectively. When combined with data from the study of inoculum levels, an overall average calculated reduction at 23 degrees C was 0.25 +/- 0.05 log CFU/month. Significantly greater reductions were observed during the 24-h drying period when broth-collected cells were used as the inoculum, suggesting that cells collected from agar lawns were more resistant to drying. However, after initial drying, the rates of reduction at 23 degrees C did not differ significantly between the inoculum preparation methods. Salmonella Enteritidis PT 30 survives for long periods on almond kernels under a variety of commonstorage conditions.     

In vitro Survival and Growth of Salmonella Typhimurium inoculated on Yolk Membrane after long Term refrigerated Storage of Shell Eggs

Salmonella enterica serovar Typhimurium has been isolated from commercial egg production facilities in the United States. Given its importance as a causative organism for food-borne salmonellosis, identifying approximate timelines for bacterial invasion of the egg is needed. The objective of this study was to examine net growth of S. Typhimurium in egg components over time. In trial 1 eggs were collected over a 24 hour period from a flock of single comb white leghorn hens while in trial 2 eggs were picked up from a commercial laying source once a week over the course of eight weeks and stored. Eggs were held at refrigeration temperature and each week, subsets of eggs were cracked, separated into yolk and albumen components, and inoculated with 10⁸ CFU/ml of novobiocin and nalidixic acid (NO/NA) resistant S. Typhimurium onto the vitelline membrane of the egg. Yolks were then covered with albumen. Eggs were incubated for twenty-four hours at 25°C. After incubation eggs were again separated into albumen, yolk, and vitelline membrane samples. In trial 1, S. Typhimurium net growth occurred in albumen by the second week and continued from 4 to 8 weeks while in trial 2 net growth only occurred at week 5 and 7. S. Typhimurium net growth on vitelline membranes occurred by 2 weeks and continued from 4 to 8 weeks in trial 1 while no net growth occurred in trial 2 over the 8 week period. Yolk samples showed no net increases in S. Typhimurium populations over the 8 week period. An erratum to this article is available at .     

In vitro Survival and Growth of Salmonella Typhimurium inoculated on Yolk Membrane after long Term refrigerated Storage of Shell Eggs

Salmonella enterica serovar Typhimurium has been isolated from commercial egg production facilities in the United States. Given its importance as a causative organism for food-borne salmonellosis, identifying approximate timelines for bacterial invasion of the egg is needed. The objective of this study was to examine net growth of S. Typhimurium in egg components over time. In trial 1 eggs were collected over a 24 hour period from a flock of single comb white leghorn hens while in trial 2 eggs were picked up from a commercial laying source once a week over the course of eight weeks and stored. Eggs were held at refrigeration temperature and each week, subsets of eggs were cracked, separated into yolk and albumen components, and inoculated with 10⁸ CFU/ml of novobiocin and nalidixic acid (NO/NA) resistant S. Typhimurium onto the vitelline membrane of the egg. Yolks were then covered with albumen. Eggs were incubated for twenty-four hours at 25°C. After incubation eggs were again separated into albumen, yolk, and vitelline membrane samples. In trial 1, S. Typhimurium net growth occurred in albumen by the second week and continued from 4 to 8 weeks while in trial 2 net growth only occurred at week 5 and 7. S. Typhimurium net growth on vitelline membranes occurred by 2 weeks and continued from 4 to 8 weeks in trial 1 while no net growth occurred in trial 2 over the 8 week period. Yolk samples showed no net increases in S. Typhimurium populations over the 8 week period.     

Multiplication in egg yolk and survival in egg albumen of Salmonella enterica serotype Enteritidis strains of phage types 4, 8, 13a, and 14b

Refrigeration of eggs is vital for restricting the multiplication of Salmonella enterica serotype Enteritidis contaminants, but differences between Salmonella Enteritidis strains or phage types in their survival and multiplication patterns in egg contents might influence the effectiveness of refrigeration standards. The present study compared the abilities of 12 Salmonella Enteritidis isolates of four phage types (4, 8, 13a, and 14b) to multiply rapidly in egg yolk and to survive for several days in egg albumen. The multiplication of very small numbers of Salmonella Enteritidis inoculated into yolk (approximately 10(1) CFU/ml) was monitored during 24 h of incubation at 25 degrees C, and the survival of much larger numbers of Salmonella Enteritidis inoculated into albumen (approximately 10(5) CFU/ml) was similarly evaluated during the first 3 days of incubation at the same temperature. In yolk, the inoculated Salmonella Enteritidis strains multiplied to mean levels of approximately 10(3) CFU/ml after 6 h of incubation and 10(8) CFU/ml after 24 h. In albumen, mean levels of approximately 10(4) CFU/ml or more of Salmonella Enteritidis were maintained through 72 h. Although a few differences in multiplication and survival were observed between individual isolates, the overall range of values was relatively narrow, and no significant differences (P < 0.05) were evident among phage types.     

Optimization of iron supplementation for enhanced detection of Salmonella Enteritidis in eggs

Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg contents. Egg contents were then incubated at 37 degrees C, and Salmonella Enteritidis colonies were enumerated for up to 106 h. Iron supplementation significantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth in egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. After 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in eggs supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reached approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts in eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of type of preenrichment and level of iron supplementation on the growth of Salmonella Enteritidis in egg contents. No significant differences in Salmonella Enteritidis counts between preenrichment and nonpreenrichment treatments were observed when egg contents were supplemented with 0.5 mg of FeSO4 per g of egg contents. It was concluded that preenrichment was not necessary for isolation of Salmonella Enteritidis from eggs. The effect of iron supplementation on the sensitivity of detection by the direct plating method was investigated. The direct plating method detected a significantly higher percentage of Salmonella Enteritidis in raw egg contents supplemented with 0.5 mg of FeSO4 per g of egg contents (90%) than in raw egg contents without iron supplementation (63.3%).     

Simple and rapid methods for detecting Salmonella enteritidis in raw eggs

The Centers for Disease Control and Prevention estimates there were 300,000 cases of Salmonella enteritidis (SE) in 1997. Egg products were associated with many of the cases. To address this problem, many producers implemented flock surveillance of the SE situation at their facilities. A rapid and simple method for detecting SE from poultry samples is critical for the effective implementation of such testing strategies. A lateral flow device for the detection of SE utilized in this study was manufactured by Neogen, Lansing, MI. The test panel is a presumptive qualitative test system that detects only members of Group D1 Salmonella species. A series of studies were conducted to optimize the test procedure for raw eggs with different sample preparations. A novel antigen extraction method was developed for use with the test panel kit. The detection limit of the test panel kit was increased approximately tenfold when the extraction method was used. Detection of SE was 100% in raw egg pools inoculated with 10 SE cells per ml of egg and incubated at a 1:10 ratio in buffered peptone water (BPW) or tetrathionate brilliant green broth (TBG) for 24 h at 37 degrees C. The developed lateral flow test kit could provide a simple, rapid, and inexpensive method for egg producers and processors to test specifically for Salmonella group D1 serovars, such as SE, in egg samples.     

Efficacy of disinfection of shell eggs externally contaminated with Salmonella enteritidis. Implications for egg testing.

Experimental contamination of the surface of shell eggs by dipping in a culture of Salmonella enteritidis resulted in the presence of Salmonella enteritidis in/on the shells as well as shell membranes but not in the egg content. Disinfection with Lugol's solution, chlorhexidine, ethanol, quarternary ammonium solutions or flaming after dipping in ethanol failed to achieve complete decontamination of the shell and membranes with resulting false positives when eggs were broken for culturing of the content. Dipping eggs for three seconds in boiling water resulted in complete destruction of Salmonella enteritidis in shells and membranes but sometimes caused the eggs to crack. A method of aseptically opening eggs without risk of contaminating the content from the shell or membrane was developed. Salmonella enteritidis deposited in/on the shell and membranes did not multiply during storage of the eggs at 20 degrees C for four weeks, the counts seemed to decrease. No Salmonella enteritidis was detected in the contents of any contaminated eggs.     

Influence of holding temperature on the growth and survival of Salmonella spp. and Staphylococcus aureus and the production of staphylococcal enterotoxin in egg products

In this study, growth and survival of Salmonella spp. and Staphylococcus aureus in steamed egg and scrambled egg held at 5, 18, 22, 37, 55 and 60 degrees C are investigated. The production of staphylococcal enterotoxin in steamed egg is also examined. Results reveal that Salmonella spp. and Staph. aureus in the egg products multiply best at 37 degrees C, followed closely by 22 and 18 degrees C. Neither pathogen showed growth in the egg products held at 5 degrees C. Initial inoculation dose, holding temperature and holding time affected the population of both organisms found in the egg products. Staphylococcal enterotoxin A (SEA) and B (SEB) are detected only in the egg products held at 37 or 22 degrees C. After holding at 37 degrees C for 36 h, scrambled egg inoculated with ca. 5.0 log cfu/g Staph. aureus contains the highest levels of SEA (> 64 ng/g) and SEB (> 64 ng/g). Although Salmonella spp. and Staph. aureus grow better in steamed eggs than in scrambled eggs, production of staphylococcal enterotoxin, in general, was higher in scrambled eggs than in steamed eggs. On the other hand, a repaid destruction of the test organisms in steamed eggs held at 60 degrees C was observed. Holding the steamed eggs at 60 degrees C, Salmonella spp. and Staph. aureus with an initial population of ca. 5.9 and 5.6 log cfu/g, respectively, reduced to a non-detectable level in 1 h.     

Effect of temperature on the growth response of Salmonella enteritidis inoculated onto the vitelline membranes of fresh eggs

The growth response of Salmonella Enteritidis (SE) on the vitelline membrane in vitro was studied with the use of a special tube devised specifically for the inoculation of SE onto the vitelline membrane and for the sampling of the yolk near the inoculation site. This latter ability allowed the detection of the movement of SE into the yolk. The growth of SE on the membrane was compared with that of SE inoculated into yolk and albumen in vitro and in ovo in fresh in-shell eggs. The incubation time was 2 days, and the incubation temperatures were 4, 8, 15, 27, and 37 degrees C. Comparison of the results obtained for in vitro growth showed that at 4, 8, and 15 degrees C, SE behaved as if it were in the albumen, with its numbers decreasing over time. At 27 and 37 degrees C, SE grew as if it were in yolk, with a maximum increase of 4.5 log CFU after 2 days at 37 degrees C. In no experiments involving growth on the vitelline membrane did SE appear in the yolk. Comparisons between in vitro and in ovo growth responses of SE in yolk and albumen indicate that SE growth on the membrane parallels that in the in-shell egg.     

Fate of unirradiated Salmonella in irradiated mechanically deboned chicken meat.

Mechanically deboned chicken meat was irradiated at 0, 1.25 and 2.50 kGy (Cesium 137) and inoculated with Salmonella dublin ATCC 15480, Salmonella enteritidis ATCC 9186 or Salmonella typhimurium ATCC 14028. Samples were then stored at 5 degrees C and 10 degrees C and were subjected to microbiological analysis directly after irradiation and inoculation (time 0), and after 24, 72, 120, 168 and 216 h of storage. Samples stored at 20 degrees C were examined at time 0 and after 6, 12 and 24 h of storage. Irradiation at 1.25 and 2.50 kGy caused an average reduction in bacterial levels of 2.23 and 3.44 logs, respectively. S. dublin, S. enteritidis and S. typhimurium showed very small, insignificant changes in numbers, during storage of meat for 9 days at 5 degrees C. The final populations of S. dublin and S. typhimurium in samples irradiated before inoculation and stored at 10 degrees C or 20 degrees C were greater than the equivalent populations in samples which had not been irradiated before inoculation. Reduction of indigenous microflora in mechanically deboned chicken meat by irradiation may create better conditions for the growth of salmonellae and may thus increase the risk of salmonellosis when accidental contamination and temperature abuse occur after a radiation treatment. Therefore, irradiated mechanically deboned chicken meat should be properly refrigerated and protected against contamination.