Salmonella enteritidis in chicken eggs

After an outbreak caused by salmonella enteritidis (SE) of which home-made mayonnaise and remoulade sauce were found to be the cause, SE was detected in ten of the remaining eggs. Subsequently 409 eggs of the next shipment from the same outlet were examined bacteriologically. Of 70 of the eggs examined, SE was found in 5 egg yolk samples and in 3 egg white samples as well as in 2 of 7 pooled shell samples. Five out of 35 pooled whole egg samples comprising a total of 349 eggs were likewise positive for SE. The isolates belonged to the phage types 4 and 7 carried the virulence plasmid pRQ29.     

预防商品鸡蛋的沙门氏菌污染

澳大利亚科学家通过观察死亡的蛤蚧卵内壳层和薄膜层,惊喜地对外宣称他们发现了沙门氏菌侵入鸡蛋的方式,但这种方式可能只是加拿大北部的特例,而且蛤蚧与商品化蛋鸡共性又很少,能否直接从蛤蚧卵推测到鸡蛋还有待考证。     

"聚焦沙门氏菌"专栏四:种蛋的沙门氏菌污染

沙门氏菌污染是种鸡场要面临的一个问题,这是因为如果种蛋及其内容物受到沙门氏菌的污染,种蛋孵出的子代雏鸡、进而引入该雏鸡的鸡场存在受到污染的可能性. 在过去一段时间中,沙门氏菌阳性种鸡群很可能将污染许多子代鸡群或鸡场,而且这种情况不只在一个国家出现. 需要指出的是,如果我们位居育种"金字塔"的顶端,也就是说处于曾祖代种鸡水平,沙门氏菌通过此金字塔向下垂直传播的后果可能会更加显著,因为更多的鸡群最终将受到污染.     

Salmonella enteritidis and other Salmonella in laying hens and eggs from flocks with Salmonella in their environment.

Seven Canadian layer flocks with Salmonella enteritidis in their environment were investigated to determine the numbers of hens infected with S. enteritidis, the localization of S. enteritidis in organs of infected hens and the numbers of S. enteritidis-infected eggs produced by two affected flocks. By a microagglutination test (MAT) using S. pullorum antigens, these flocks had more seropositive hens (mean 51.9 +/- 16.9%) than two Salmonella-free flocks (mean 13.0 +/- 4.2%). Culture of tissues of 580 hens (433 seropositive) from the seven flocks detected 26 (4.5%) S. enteritidis-infected hens from two flocks. In one flock, 2/150 hens were infected with S. enteritidis phage type (PT) 8, which was confined to the ceca, and no Salmonella spp. were isolated from 2520 eggs (one day's lay). In the second flock, where 24/150 hens were infected with S. enteritidis PT13, extraintestinal infection was found in nine hens and involved the ovaries and/or oviduct in two hens. Salmonella enteritidis PT13 was isolated from one sample of egg contents and from one sample of cracked shells from among 14,040 eggs (one day's lay) from this flock. The overall prevalence of S. enteritidis-contaminated eggs from the two flocks with infected hens was less than 0.06%. Other Salmonella spp. isolated were S. heidelberg from 58 hens (10%), and S. hadar, S. mbandaka and S. typhimurium from one hen (0.2%) each. The MAT with antigens of S. pullorum had a sensitivity of 81% and a specificity of 24% for detecting S. enteritidis-infected hens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Introduction: Reducing Salmonella Enteritidis contamination of shell eggs

Salmonella Enteritidis is a leading food-borne pathogen in the United States, with many outbreaks in humans traced back to shell eggs. As a result, the implementation of effective strategies for reducing Salmonella Enteritidis in commercial layer flocks has become a critical public health and economic objective. In this paper, we share the findings of 2 multistate USDA-National Integrated Food Safety Initiative grant teams and their work aimed at Salmonella Enteritidis reduction in shell eggs. One project, led by K. Venkitanarayanan, is using plant-derived antimicrobial molecules as dietary supplements to reduce Salmonella Enteritidis colonization of the digestive and reproductive tract of chickens. The same molecules are being evaluated for their effect on Salmonella Enteritidis in egg wash solutions. The project led by S. Kariyawasam used on-farm investigation and novel bacterial typing methods to study Salmonella Enteritidis transmission in diverse layer environments to update and optimize Egg Quality Assurance Programs that will significantly reduce Salmonella Enteritidis contamination of shell eggs. The current US Food and Drug Administration Egg Safety Rule and Egg Quality Assurance Programs are based on critical control points and best management practices developed from studies of large flocks (>50,000 hens) conducted in the 1990s, indicating that opportunities exist to improve preharvest programs to reduce Salmonella Enteritidis contamination. This paper will share the findings of these 2 projects.     

Production of Salmonella enteritidis-contaminated eggs by experimentally infected hens

Laying hens of three different ages were experimentally infected with a strain of Salmonella enteritidis by either oral inoculation or contact transmission. Total egg production was depressed in exposed hens of all three age groups. Persistent intestinal shedding was observed in a small number of hens. Eggs with contents contaminated by S. enteritidis were produced by exposed hens at a high frequency, but only during a fairly short period of time that extended through approximately 1 week postinoculation for older hens and through 2 weeks for younger hens. S. enteritidis was recovered from whole yolks and albumen of these eggs at similar frequencies, but not from the content of yolks. Eggs with contaminated shells were also produced, but at a lower frequency. Contaminated eggs were produced by orally inoculated and contact-exposed hens at similar frequencies. S. enteritidis was not isolated from the contents of eggs laid by hens infected with other S. enteritidis strains.     

Salmonella typhimurium penetration through the eggshell of hatching eggs

This study was undertaken to demonstrate penetration of Salmonella typhimurium through the eggshell of newly laid broiler hatching eggs. Eggs were challenged either by lightly spraying the bacteria over the blunt end of the egg or by contact with contaminated dry nest litter. Exposure time for both groups was 10 minutes; afterward, all eggs were disinfected and incubated 19 days under normal conditions. Chorioallantoic membranes and yolk sacs were cultured in brain-heart infusion broth on day 19 to demonstrate penetration. Isolation of the bacteria from chorioallantoic membranes and yolk sacs, respectively, were as follows: sprayed group: 100% and 83%; contact group: 59% and 29%. These results showed that although water enhanced S. typhimurium penetration, its presence on the eggshell is not essential for penetration to occur.     

Detection of Salmonella in spent hens and eggs associated with foodborne infections

About 16,000 spent hens from 23 farms in the northern area of Japan were purchased in 1996, 1997, 1998, and 1999 to isolate Salmonella in two poultry processing plants. Salmonella was detected in 12 of 23 farms (52.2%). In particular, the serotypes Enteritidis and Infantis were detected in four and three farms, respectively. The prevalence rates in the hens' ceca, immature eggs, and the yolk of mature eggs in oviducts were 14%, 7.2%, and 6.8%, respectively. A total of 23 serotypes were detected. The major serotypes of the strains were Enteritidis, Corvallis, Typhimurium, and Infantis, but most of the strains were untypable. In the same area during 1992 to 1996, Salmonella was detected in eggs associated with four outbreaks of Salmonella Enteritidis infection and one outbreak of Salmonella Infantis infection. The ratio of contamination was approximately 1%, and the level was estimated to be 93 MPN(most probable number)/100 g in one outbreak. In farms that produced the eggs associated with all of the five outbreaks of Salmonella, the serotype Enteritidis or Infantis was isolated from hens. Farms where Salmonella was not detected were not related to any of the outbreaks.     

Integrated farm management to prevent Salmonella Enteritidis contamination of eggs

Salmonella Enteritidis in contaminated eggs is a public health hazard that may cause hospitalization or death in the elderly, infants, and individuals with impaired immune systems. Prevention of Salmonella Enteritidis infection of laying hens is an essential first step in reducing Salmonella Enteritidis outbreaks in humans. Multiple interventions at several stages during egg production can combine to reduce numbers of infected chickens and keep egg contamination to low levels. Every effort should be made to exclude Salmonella Enteritidis from egg production premises by implementing effective biosecurity measures, stocking the farm with Salmonella Enteritidis-free replacement pullets, controlling rodent and insect vectors, and denying wild birds and pets access to chicken houses. Diligent cleaning and disinfection of chicken houses before introduction of a new flock will minimize environmental exposure and indirect horizontal transmission of multiple pathogens, including Salmonella Enteritidis. Increased resistance of chickens to intestinal colonization by Salmonella Enteritidis can be attained by the use of probiotics, prebiotics, and synbiotics. Laying hens should be immunized with live and killed vaccines to stimulate mucosal and systemic immunity and reduce the prevalence of Salmonella Enteritidis-contaminated eggs. Shell eggs should be refrigerated as soon as possible after laying to keep Salmonella Enteritidis cells at low levels in any contaminated eggs. Comprehensive Salmonella Enteritidis-control programs have proven to be successful in reducing the incidence of Salmonella Enteritidis infections in both egg-laying flocks and humans.     

Salmonella contamination of hatching and table eggs: a comparison.

This study determined and compared Salmonella contamination rates of pools of surplus, early and culled hatching eggs from layer and broiler breeder flocks, and of pools of early and regular table eggs from layer flocks. Each pool contained 6 eggs. Five methods were used for the isolation of Salmonella. Nine of 126 pools of culled layer hatching eggs, 2 of 126 pools of surplus layer hatching eggs, and one of 126 pools of early layer hatching eggs were contaminated with Salmonella. All 126 pools of broiler breeder surplus, and early and culled hatching eggs tested negative for Salmonella. All 168 pools of regular table eggs tested negative for Salmonella, whilst one of 84 pools of early table eggs contained Salmonella agona. The pools of culled layer hatching eggs and surplus layer hatching eggs that contained S. typhimurium were derived from the same breeder operation. Similarly, the pools of culled and early layer hatching eggs that contained S. heidelberg were derived from one breeder operation. Pools of culled hatching eggs were more frequently contaminated with Salmonella than other hatching or table eggs. Pools containing eggs that were both cracked and dirty were more frequently contaminated with Salmonella than all other pools of eggs. The overall Salmonella contamination rate of the table eggs was 0.07 to 0.4%. Critical control points (macroscopic classification of the eggs as cracked and dirty) were validated microbiologically.     

Effect of time and temperature on growth of Salmonella enteritidis in experimentally inoculated eggs

Influence of time and temperature on Salmonella enteritidis multiplication in experimentally injected eggs was examined. There was an increase in the number of S. enteritidis with the increase in temperature of egg storage. There was less increase of S. enteritidis in eggs stored at 4 degrees C than in eggs held at temperatures higher than 4 degrees C (P less than 0.05). These results suggest a possible method for monitoring commercial eggs for the presence of S. enteritidis. It was concluded that the chances of recovery of S. enteritidis can be increased 10(6)-fold or more by holding the eggs at temperatures of 21 or 27 degrees C for more than 20 days and culturing their contents.     

Occurrence of Salmonella enteritidis in pooled table eggs and market-ready chicken carcasses in Zambia.

The level of Salmonella enteritidis contamination in Zambian table eggs and ready market chicken carcasses was studied. Nine of the 240 (3.8%) pooled samples of table eggs and 18 of 382 (4.7%) chicken carcasses were contaminated with S. enteritidis. All the isolates from the table eggs belonged to the enteropathogenic invasive phage type 4, whereas seven isolates from the chicken carcasses belonged to phage type 4, three were phage type 7, and eight were untypable (rough type). All the isolates were sensitive to gentamycin, ampicillin, tetracycline, cotrimoxazole, amoxycillin, furazolidone, and chloramphenicol.     

Detection of antibody to Salmonella enteritidis and S typhimurium in the yolk of hens' eggs

Enzyme-linked immunosorbent assays (ELISAs) have been developed to detect IgG antibodies to Salmonella enteritidis and S typhimurium in the yolk of hens' eggs. Better discrimination and more consistent results were obtained between eggs from experimentally infected and uninfected hens by using saline-dilution of yolk rather than chloroform extraction. Threshold absorbance values were determined in three salmonella-free flocks, and on the basis of these results ELISA optical density values greater than 0.25 were considered to be positive for antibodies to salmonella. Four flocks with a history of salmonella infection were examined; three contained birds which were seropositive for S enteritidis by ELISA and from which S enteritidis was isolated, and a large proportion of eggs from these birds contained antibody to S enteritidis. Eggs from the fourth flock had no detectable antibody, although serum antibody was detected in some birds. No salmonellae were isolated from the yolks of the eggs from any of the four flocks.     

Emergence of Salmonella enterica serovar Potsdam as a major serovar in waterfowl hatcheries and chicken eggs

Salmonellosis is a common food-borne illness in humans caused by Salmonella-contaminated poultry and their products. In hatcheries, 110 Salmonella isolates were identified, mostly from first enrichment, and few from delayed enrichment. The Salmonella prevalence in goose and duck hatcheries was higher when measured by four multiplex PCR methods than by traditional culture (73.8% vs. 44.35%, P < 0.05); 97.3% of 110 isolates were Salmonella Potsdam of serogroup C1 and other isolates were Salmonella Montevideo of C1 and Salmonella Albany of C2. Plasmid and pulsed field gel electrophoresis genetic analysis revealed that isolates from duck hatcheries were more diverse than those from goose hatcheries. In Salmonella Potsdam, host species-specific genotypes were observed in geese for genotypes 3, 4, and 5 and in ducks for genotypes 7, 8, and 9, suggesting that Salmonella Potsdam may evolve into goose- and duck-specific isolates. An examination of 1121 eggs found that only Salmonella Potsdam was identified in 1.8% (7/591) of eggs from chickens fed on the ground, not housed in cages, and in egg content (6/7) as well as eggshell membrane (1/7). In conclusion, Salmonella Potsdam may be a major Salmonella infection in waterfowl and chicken eggs.     

Eggshell penetration of hen's eggs by Salmonella enterica serovar Enteritidis upon various storage conditions

1. The survival and penetration of Salmonella enterica serovar Enteritidis (SE) inoculated on the eggshell was examined upon storage for up to 20 d at real-life conditions (15 to 25 degrees C and 45 to 75% relative humidity (RH)). 2. Penetration was assessed by emptying the egg contents and filling the eggs with a selective medium that allowed visualising Salmonella growth on the inside of the shell and membrane complex. 3. The study of survival on the eggshells was based on viable counts and showed that numbers of surviving organisms decreased over time. Survival was inversely related to storage temperature and RH. Although the average counts decreased over time, a limited proportion of shells carried high numbers of SE at all storage conditions. 4. Penetration spots were observed earlier using an increased storage temperature due to increased growth rates of SE on the agar. After 20 d of storage a similar percentage (c. 44.7%) of eggshells became penetrated, irrespective of the storage conditions tested in this study. 5. The higher the Salmonella shell contamination at the end of storage, the higher the probability that the eggshell was penetrated. Salmonella shell counts exceeding 4 log cfu yielded more than a 90% probability of eggshell penetration occurring.