Multiplication of Salmonella enteritidis on the yolk membrane and penetration to the yolk contents at 30 degrees C in an in vitro egg contamination model

Refrigeration to limit bacterial multiplication is a critical aspect of efforts to control the transmission of Salmonella enterica serovar Enteritidis (SE) to consumers of contaminated eggs. Although the nutrient-rich yolk interior is an uncommon location for SE contamination in freshly laid, naturally contaminated eggs, migration across the vitelline membrane could lead to rapid bacterial multiplication even when the initial site of deposition is outside the yolk. Multiplication on the yolk membrane (before, or in addition to, multiplication within the yolk contents) could be another source of increased risk to consumers. The present study used an in vitro egg contamination model to compare the abilities of four strains of SE to either multiply in association with the yolk membrane or migrate through that membrane to reach the yolk contents during 36 h of incubation at 30 degrees C. After inoculation onto the exterior surface of intact, whole yolks, all four SE strains penetrated the vitelline membrane to reach the yolk contents (at an overall frequency of 11.5%) after 12 h of incubation. The mean log concentration of SE was significantly higher in whole yolks (including yolk membranes) than in yolk contents at both 12 h (0.818 versus 0.167 CFU/ ml) and 36 h (2.767 versus 1.402 CFU/ml) of incubation. These results demonstrate that SE multiplication on the vitelline membrane may both precede and exceed multiplication resulting from penetration into the yolk contents during the first 36 h of unrefrigerated storage, reinforcing the importance of rapid refrigeration for protecting consumers from egg-transmitted illness.     

Effect of refrigeration on in vitro penetration of Salmonella enteritidis through the egg yolk membrane

Internally contaminated eggs have been implicated as leading sources of transmission of Salmonella Enteritidis (SE) to humans. Although SE is not often deposited inside the nutrient-rich yolks of naturally contaminated eggs, penetration through the vitelline membrane to reach the yolk contents could result in rapid bacterial multiplication. In previous studies, such penetration has been observed occasionally at warm temperatures during experiments with in vitro egg contamination models. The present study was conducted to determine whether refrigeration affects the frequency of in vitro SE penetration of the egg yolk membrane. After inoculation of small numbers of SE onto the outside of the vitelline membranes of intact yolks, immediate refrigeration of contaminated samples prevented the penetration of SE into the egg yolk contents during 24 h of storage. However, SE penetrated inside the yolk contents in 4% of contaminated egg samples refrigerated after 2 h of storage at 30 degrees C, 15% of samples refrigerated after 6 h of storage at 30 degrees C, and 40% of samples stored at 30 degrees C for 24 h (48 samples per treatment group). These results highlight the value of prompt refrigeration for restricting the opportunities for SE to multiply to high numbers inside the yolks of contaminated eggs.     

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.     

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.     

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.     

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.     

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.     

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.     

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 .     

Thermal death time measurement using thin flexible sleeves: a new experimental approach for determining microbial destruction kinetics in fluids of arbitrary viscosity

The thermal death time kinetics of Salmonella Enteritidis (SE) was measured in buffer, egg yolk, and albumen using thin layer plastic sleeves. The sleeves allowed for the loading and sampling of liquids of high or unusual viscosity, as in the case of yolk and albumen, and accepted relatively large volumes (2 to 3 ml) of fluid. The sleeves maintained the volume of the fluid in a thin layer and could be easily handled for heat exposure. The thin layer maintained one-dimensional heat transfer and minimized temperature gradients, thus preventing parts of the fluid from experiencing different heating rates. A representative strain of SE associated with an egg-based salmonellosis outbreak was used in this study. The D- and z-values of the chosen strain, H7037, were measured in buffer, yolk, and albumen. In buffer, SE had the following mean (±standard deviation) D-values: D(55°C) = 3.51 ± 0.30 min, D(57°C) = 1.75 ± 0.13 min, and D(60°C) = 0.25 ± 0.06 min. In yolk, D(58°C) = 0.90 ± 0.05, D(60°C) = 0.26 ± 0.03, and D(62°C) = 0.20 ± 0.02. In albumen, D(55°C) = 1.26 ± 0.31, D(56°C) = 0.68 ± 0.10, and D(57°C) = 0.44 ± 0.04. The z-values for SE calculated from these D-values were 4.29 ± 0.39°C in buffer, 6.12 ± 0.26°C in yolk, and 4.63 ± 1.14°C in albumen. The sleeves allowed one consistent approach to determining thermal death time kinetics regardless of viscosity.     

Survival of Escherichia coli O157:H7 and Campylobacter jejuni in bottled purified drinking water under different storage conditions

Survival of Escherichia coli O157:H7 and Campylobacter jejuni that were separately inoculated into bottled purified drinking water was investigated during storage at 22, 4, and -18 °C for 5, 7, and 2 days, respectively. Two inoculation levels were used, 1 and 10 CFU/ml (10(2) and 10(3) CFU/100 ml). In samples inoculated with 10(2) CFU/100 ml, C. jejuni was not detectable (>2-log reduction) after storage under the conditions specified above. E. coli O157:H7 was detected on nonselective and selective media at log reductions of 1.08 to 1.25 after storage at 22 °C, 1.19 to 1.56 after storage at 4 °C, and 1.54 to 1.98 after storage at -18 °C. When the higher inoculation level of 10(3) CFU/100 ml was used, C. jejuni was able to survive at 22 and 4 °C, with 2.25- and 2.17-log reductions, respectively, observed on nonselective media. At these higher inoculation levels, E. coli O157:H7 was detectable at 22, 4, and -18 °C, with log reductions of 0.76, 0.97, and 1.21, respectively, achieved on nonselective media. Additionally, E. coli O157:H7 showed significant differences in culturability (P<0.05) on the nonselective and selective culture media under the different storage conditions, with storage at -18 °C for 2 days being the treatment most inhibiting. The percentage of sublethal injury of E. coli O157:H7 ranged from ～33 to 75%, indicating that microbial examination of bottled water must be done carefully, otherwise false-negative results or underestimation of bacterial numbers could pose a health risk when low levels of pathogens are present.     

储存温度对鸡蛋微生物及品质的影响

为了解温度对鸡蛋中各组分微生物生长的影响,对鸡蛋在8、10、20、25℃储存30d内的蛋壳、蛋清和蛋黄的细菌总数变化规律做初步研究,并分析储存终点时鸡蛋的气室深度、蛋黄指数、浓蛋白含量、挥发性盐基氮含量品质指标。结果表明：储存温度对鸡蛋各部分细菌总数影响较大。8℃储存30d时蛋壳、蛋清和蛋黄细菌总数分别为3.5×103、2.4×103、1.7×103CFU/g,而25℃储存时则分别达4.6×106、7.5×104、5.3×105CFU/g。8℃和10℃储存10d内,蛋清和蛋黄中均未检测到细菌,25℃储存时则分别在第5天和第10天从蛋清和蛋黄中检测到细菌。鸡蛋各项品质指标的测定结果也表明储存温度越高鸡蛋品质越差。     

The vitelline membrane: Dynamics of cholesterol metabolism in hens' eggs

Changes in cholesterol levels in egg contents were studied to indicate trends and dynamics of processes of penetration through the vitelline membrane from yolk to egg white. Investigations were carried out on eggs stored for a period of 35 days at room temperature (22°C). Levels of free and esterified cholesterol were determined by the spectrophotometric method at 7-day intervals. The selective character of the vitelline membrane depends on conditions and period of storage. The study demonstrated that the vitelline membrane loses its selective nature between the twentieth and thirtieth days under particular conditions of storage. Following this period, a spontaneous penetration of cholesterol into the egg white is observed—i.e. the barrier equilibrium of the membrane becomes unstable. The presence of free cholesterol in egg white may be indicative of loss of egg freshness.     

鲜鸡蛋中溶菌酶的活性分布

为了研究鸡蛋不同部位溶菌酶的活性,在不破坏蛋体内部结构的情况下,利用注射器和照蛋器抽取蛋内样品(系带与蛋黄膜除外),对鲜鸡蛋各个部分的溶菌酶活性进行分析研究。结果表明：壳外膜及蛋黄中不含溶菌酶,蛋黄膜所含溶菌酶活力最高为9764.290U/mL,其次系带为4172.86U/mL,系带中溶菌酶活力约为其他部位溶菌酶活力的11倍以上;蛋膜黏附蛋白、外稀蛋白、中浓蛋白和内稀蛋白这4个部位所含溶菌酶活力分别为378.714、 330.238、354.929、245.381U/mL,壳外膜和蛋黄不含有溶菌酶。蛋清在蛋内的位置不同,其中溶菌酶活力也存在差异,尖中部及钝端的溶菌酶活性高,而尖端及蛋的中部溶菌酶活性低。     

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.     

GROWTH, SURVIVAL AND HEAT RESISTANCE OF SALMONELLA TYPHIMURIUM AND ESCHERICHIA COLI IN REGULAR AND OMEGA-3 HENS EGG PRODUCTS

Omega‐3 enriched eggs are currently produced by hens fed a flax diet. Since omega‐3 polyunsaturatedfatty acids are prone to oxidation, the addition of vitamin E is supplemented into the hen's diet as an antioxidant. Typically these eggs contain about 2 and 4 times more omega‐3 fatty acids and vitamin E, respectively compared to regular eggs. Since table eggs have a long history of association with foodborne salmonellosis, it was of interest to compare the growth and/or survival of several bacterial pathogens in omega‐3 and regular eggs. In this respect nalidixic‐resistant Escherichia coli and Salmonella Typhimurium were inoculated into regular and omega‐3 hen's egg products (whole eggs, albumen, yolk) and incubated at 22, 8 and ?20C. Time‐course studies indicated that by 72 h both Salmonella and E. coli levels increased by 7 logs at 22C in both types of whole egg. At 8C population levels for these bacteria both increased by approximately 3 logs at 6 weeks. In regular and omega‐3 yolks, salmonellae maintained at 22 and 8C for 48 h and 6 weeks increased by approximately 6 and 1.5 logs, respectively. E. coli levels were higher in egg yolk compared to Salmonella at both temperatures. Regardless of the yolk source, however, no significant (P > 0.05) differences in population levels were observed. Survival patterns of E. coli at ?20C were not significantly (P > 0.05) different between whole egg sources. This trend was also observed in the yolks. For Salmonella no significant (P > 0.05) differences in survival were observed between yolk preparations maintained at ?20C. Increasing the level of α‐tocopherol from c. 63 to 240 ppm in regular egg yolk, resulted in no significant (P > 0.05) differences in the growth of Salmonella at 22C. In addition, when the bacterium was heated in regular egg yolk amended with vitamin E at 56.5C, no significant (P > 0.05) difference was observed in resistance regardless of α‐tocopherol (55‐713 ppm) or total tochopherol (92–1238 ppm) level.     

Inactivation of Salmonella in Shell Eggs by Hot Water Immersion and Its Effect on Quality

Thermal inactivation kinetics of heat resistant strains of Salmonella Enteritidis in shell eggs processed by hot water immersion were determined and the effects of the processing on egg quality were evaluated. Shell eggs were inoculated with a composite of heat resistant Salmonella Enteritidis (SE) strains PT8 C405, 2 (FSIS #OB030832), and 6 (FSIS #OB040159). Eggs were immersed in a circulating hot water bath for various times and temperatures. Come‐up time of the coldest location within the egg was 21 min. SE was reduced by 4.5 log at both hot water immersion treatments of 56.7 C for 60 min and 55.6 °C for 100 min. Decimal reduction times (D‐values) at 54.4, 55.6, and 56.7 °C were 51.8, 14.6, and 9.33 min, respectively. The z‐value was 3.07 °C. Following treatments that resulted in a 4.5 log reduction (56.7 °C/60 min and 55.6 °C/100 min), the surviving population of SE remained static during 4 wk of refrigerated storage. After processing under conditions resulting in 4.5 log reductions, the Haugh unit and albumen height significantly increased (P < 0.01) and yolk index significantly decreased (P < 0.05). The shell dynamic stiffness significantly increased (P < 0.05), while static compression shell strength showed no significant difference (P < 0.05). Vitelline membrane strength significantly increased (P < 0.05); although, no significant difference (P < 0.05) was observed in vitelline membrane elasticity. In summary, the hot water immersion process inactivated heat resistant SE in shell eggs by 4.5 log, but also significantly affected several egg quality characteristics.     

Incubation of supplemented egg contents pools to support rapid detection of Salmonella enterica serovar Enteritidis

Detecting internal contamination of eggs with Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) is an important aspect of efforts to identify infected laying flocks. When egg contents pools are tested for Salmonella Enteritidis, a preliminary incubation step is often employed to allow small initial populations of contaminants to multiply to more easily detectable numbers. Consistent detection of Salmonella Enteritidis in egg pools by direct plating requires the presence of at least 10(5) CFU/ml, whereas some very rapid methods can require as many as 10(7) CFU/ml. The present study determined the rates at which initial inocula of approximately 10 Salmonella Enteritidis cells multiplied in 10-egg pools, some of which were supplemented with concentrated nonselective enrichment broth or with a source of iron. At 37 degrees C, Salmonella Enteritidis concentrations in supplemented egg pools usually reached 10(5) CFU/ml within 12 h and 10(7) CFU/ml by 12 to 15 h of incubation. At 25 degrees C, Salmonella Enteritidis concentrations in supplemented egg pools typically attained 10(5) CFU/ml by 18 to 27 h and 10(7) CFU/ml by 27 to 36 h of incubation. At both temperatures, Salmonella Enteritidis multiplication was significantly slower in unsupplemented pools. Accordingly, the length of incubation time necessary for consistent detection of small numbers of Salmonella Enteritidis in egg contents pools depends on the incubation temperature used, on whether the egg pools are supplemented to increase the rate of bacterial multiplication, and on the sensitivity of subsequent tests applied to the incubated pools.     

COMPARISON OF FROZEN, FOAM-SPRAY-DRIED, FREEZE-DRIED AND SPRAY-DRIED EGGS

SUMMARY —Coagulation patterns of slurries prepared with milk and frozen, foam-spray-, freeze-and spray-dried whole eggs, yolks and albumen were studied. All slurries were heated and stirred at constant rates using a Brabender Visco/Amylo/Graph. Ranked in order of initial gelation temperatures were slurries prepared with frozen, freeze-, spray- and foam-spray-dried whole eggs. Slurries prepared with frozen yolks or albumen showed initial gelation at lower temperatures than those prepared with dried yolks or albumen. Viscosity data indicate detrimental effects of drying to gelation properties of whole eggs, yolks and albumen.     

Effects of different molting procedures on incidence of Salmonella infection in flocks of naturally contaminated laying hens in a commercial egg-producing farm by detection of yolk antibodies to Salmonella in eggs

Indirect enzyme-linked immunosorbent assays (ELISAs) have been applied to detect immunoglobulin Y antibodies to different serotypes of Salmonella in the yolks of chicken eggs with heat-extracted antigens of Salmonella enterica serotypes Agona (SA), Cerro (SC), Enteritidis (SE), Montevideo (SM), and Putten (SP). The egg yolk samples examined were classified as positive if their ELISA absorbance values exceeded the value for eggs from specific-pathogen-free flocks by more than two standard deviations. Of 30 egg yolk samples from three flocks vaccinated with a killed SE vaccine, 29 were antibody positive by the ELISA assay for the SE antigen. Four to 29 of the 29 yolk samples showed positive results for the other serovars, although the absorbance values for SE were higher than those obtained for the other serotypes in each of the yolk samples. All 30 yolks from three flocks that were not administered any SE vaccines were found to be antibody negative for SE, and two samples were determined to be positive for SC. Thirty-nine or 40 eggs were obtained from each of four layer flocks in a commercial egg production farm where the laying houses were naturally contaminated with SA, SC, SM, SP, Salmonella serovar Infantis (SI), and untypeable strains. The ELISA absorbance values for SM in the egg yolks obtained from the two flocks molted through feed withdrawal when the birds restarted laying were significantly (P < 0.05) higher than those observed in the yolks obtained before the molt. In egg yolks from the two other flocks that were molted through a wheat bran diet, there was no significant difference between the absorbance values before and after the molt. The observations in the present study provide further evidence to suggest that a molt initiated through the administration of a wheat bran diet can reduce the risk for Salmonella problems in a commercial egg-producing setting.