Interrelationships between strains of Salmonella enteritidis.

In contrast to S. typhimurium [19], S. enteritidis is a serotype which has its primary food-animal reservoir in poultry. To date, phage typing has been of paramount importance in studying the epidemiology of this serotype and in particular, has demonstrated the involvement of both poultry meat and whole shell eggs in the transmission of S. enteritidis PT4 to humans. The findings discussed above describe various aspects of the serotype, particularly in relation to the involvement of both LPS and plasmids in its virulence and phage type identity (Fig. 2). These findings have led to an increased understanding of the biology of this serotype, which is of major importance in human food-poisoning in England and Wales at the present time.     

Bavaroise and an epidemic of Salmonella enteritidis

In the literature an association is made between the increasing prevalence of Salmonella enteritidis in poultry products and in the isolates of patients with gastroenteritis, without sufficient evidence of a causal relationship between the increasing prevalences. A microbiological and epidemiological analysis of a food poisoning incident among 239 visitors of a restaurant by way of food specific attack rates and food specific infection rates revealed an epidemic of 70 cases of S. enteritidis enteritis. The analysis supports the causal relationship with the consumption of an infected, unhygienically prepared egg product, in this case bavaroise.     

Epidemiological study of Salmonella enteritidis strains of animal origin in Belgium

Since 1987, the number of cases of salmonellosis caused by Salmonella enteritidis has considerably increased in Western Europe. Comparison of endemic animal strains isolated in Belgium from 1976-84 with strains isolated from 1987 on shows that the strains which cause the current epidemic have no features distinguishing them from the previously-isolated strains and that furthermore, they do not constitute a bacterial clone. They belong to 13 different lysotypes and in most cases remain sensitive to antibiotics. Nevertheless, the lysotype 33 (which belongs to the phage type 4 has increased significantly. It encompasses 37% of the animal strains isolated in Belgium from 1987-9, but only 7% of the strains isolated from 1976-84. It is worth noting that the endemic as well as the epidemic strains contain a virulence plasmid sharing sequence similarities with the FIB and FIIA plasmid replicons and with the VirA and VirB virulence regions of the S. typhimurium virulent plasmid: pIP1350.     

The prevalence of Salmonella enteritidis and other Salmonella spp. among Canadian registered commercial layer flocks

A survey was conducted to estimate the prevalence of Salmonella enteritidis and other salmonellas among Canadian commercial egg producing flocks. Environmental (faecal and eggbelt) samples from 152 of 295 (52.9%) randomly selected flocks were contaminated with salmonellas. Thirty-five different salmonella serovars were isolated. Eggbelt samples were more often contaminated with salmonellas than faecal samples (25.7 v. 10.1%). The most prevalent serovars were S. heidelberg, S. infantis, S. hadar, and S. schwarzengrund; they were isolated from samples of 59/295 (20%), 18/295 (6.1%), 17/295 (5.8%), and 15/295 (5.1%) flocks, respectively. Feed samples of 21/295 (7.2%) flocks were contaminated with salmonellas. Salmonella enteritidis was isolated from the environmental samples of 8/295 (2.7%) flocks. Salmonella enteritidis phage type (PT) 8 was isolated from 5 flocks, PT 13a from 2 flocks, and PT 13 from 1 flock.     

The prevalence of Salmonella enteritidis and other Salmonella sp. among Canadian registered commercial chicken broiler flocks

A nation-wide survey was conducted to estimate the prevalence of Salmonella enteritidis and other salmonellas among Canadian commercial broiler flocks. Environmental (litter and/or water) samples from 226 of 294 (76.9%) randomly selected flocks were contaminated with salmonellas. Litter samples were more often contaminated with salmonellas than water samples (47.4 v. 12.3%). Fifty different salmonella serovars were isolated. The most prevalent serovars were S. hadar, S. infantis, and S. schwarzengrund; they were isolated from samples of 98/294 (33.3%), 26/294 (8.8%), and 21/294 (7.1%) flocks, respectively. Feed samples of 39/290 (13.4%) flocks were contaminated with salmonellas. Salmonella enteritidis was isolated from the environmental samples of 9/294 (3.1%) flocks. Salmonella enteritidis phage type (PT) 8 was isolated from seven flocks, and PT 13a from two flocks.     

Antimicrobial susceptibility and phage types of Salmonella enteritidis strains isolated in the Lublin area

The study aimed at specifying the value of two traditional methods of typing, using the collection of 241 strains of Salmonella Enteritidis isolated from people and animals in the Lublin area in 1994-1995 from the occasional cases of infections. There were 8 phage types identified among the examined strains. Phage types PT 6 (40.24% of strains) and PT 7 (29.46%) were the most numerous ones. Salmonella Enteritidis was numbered among 38 profiles on the basis of the analysis of resistance to 15 antimicrobial agents. It was found that nitrofurantoin had the lowest efficacy in vitro in relation to the examined collection of Salmonella isolates. High percentage of strains were characterized by lack of susceptibility to streptomycin, neomycin, cefixime, tetracycline and canamycine. While analyzing the profiles of resistance to chemiotherapeutics and the expression of phage type of the examined strains it was observed that only 14.1% of all strains showing resistance to nitrofurantoin represented at the same time phage type PT 6, whereas 10.8% of strains belonging to the same resistance profile indicated PT 7 phage type. In correlated analysis of resistance to chemiotherapeutics and phage type expression of the examined collection of 241 isolates of Salmonella Enteritidis, 18.3% of strains showed distinct and unique set of these two features, which can be used in epidemiological investigations for the preliminary characterization of the bacterial population.     

Dose-response effects in an outbreak of Salmonella enteritidis.

The effects of ingested Salmonella enteritidis (SE) dose on incubation period and on the severity and duration of illness were estimated in a cohort of 169 persons who developed gastroenteritis after eating hollandaise sauce made from grade-A shell eggs. The cohort was divided into three groups based on self-reported dose of sauce ingested. As dose increased, median incubation period decreased (37 h in the low exposure group v. 21 h in the medium exposure group v. 17.5 h in the high exposure group, P = 0.006) and greater proportions reported body aches (71 v. 85 v. 94%, P = 0.0009) and vomiting (21 v. 56 v. 57%, P = 0.002). Among 118 case-persons who completed a follow-up questionnaire, increased dose was associated with increases in median weight loss in kilograms (3.2 v. 4.5 v. 5.0, P = 0.0001), maximum daily number of stools (12.5 v. 15.0 v. 20.0, P = 0.02), subjective rating of illness severity (P = 0.0007), and the number of days of confinement to bed (3.0 v. 6.5 v. 6.5, P = 0.04). In this outbreak, ingested dose was an important determinant of the incubation period, symptoms and severity of acute salmonellosis.     

Genetic relationships among strains of Neisseria meningitidis causing disease in Italy, 1984-7

Since 1984 a change in the epidemiological pattern of meningococcal disease in Italy has occurred with a predominance of Neisseria meningitidis of serogroup C (76%), serotype 2a and a high proportion of strains resistant to sulphonamides (71%). In order to understand better the epidemiology of the group C N. meningitidis strains responsible for the disease over the last years in Italy, we studied the genetic features of phenotypically closely related strains, by enzyme electrophoresis. The results showed that the genetic and the phenotypic characteristics of the 57 strains studied were similar, suggesting that spread of a single clone during recent years in our country. This result is in agreement with the circulation of strains typical of epidemic situations, despite the decreasing incidence of meningococcal disease in Italy.     

Salmonella enteritidis outbreak in a home for the aged

BACKGROUND: An outbreak of gastroenteritis caused by Salmonella Enteritidis (SE), phagotype 1, reported at a senior citizen living facility in Burgos on November 15, 1999 is discussed. The objective of the research of this outbreak was that of ascertaining the source of infection, the mechanism by which it was transmitted and to propose the suitable measures for preventing any recurrence of this problem. METHODS: An observational retrospective cohort study has been made by surveying 106 of a total of 119 residents and 9 employees at the center in question. The Relative Risk of being affected by this disorder has been estimated in terms of the intake of different foods. Logic Regression was employed for calculating the odds ratio adjusted by age, sex and by the intake of foods and wine. The concordance of the clinical diagnosis with the coproculture diagnosis was studied using the Cohen's Kappa index of agreement. RESULTS: A total of 42 individuals reported symptoms (37 residents and 5 employees). The clinical attack rate was 36.5%. Forty-five (45) of the 91 coprocultures performed (82 on residents and 9 on employees) were positive (41 in residents and 4 in employees). The attack rate for cases confirmed by coproculture was 49.5% among those investigated. Fried breaded milk and flour batter sweets was the food product implicated epidemiologically with the onset of the outbreak: RR 3.25 (C.I at 95% 1.10-9.59). The protective effect of the wine (Odds Ratio: 0.68) was not high enough to be statistically significant (p = 0.36). The Kappa index was 0.43 (p < 0.001), which reveals very little agreement between the clinical diagnosis and the coproculture diagnosis. CONCLUSIONS: Epidemiological evidence exists of the intake of fired breaded milk and flour batter sweets having been the mechanism for the transmission of the infection, and the food product in question having been stored at room temperature having been the determining contributing factor in the start of the outbreak. This reveals that the best way of preventing this type of outbreaks are clean habits and practices on the part of all those involved in the food-handling sector.     

Molecular characterization of plasmids in Salmonella enteritidis phage types.

Plasmids in selected type strains of 26 of the Salmonella enteritidis phage types have been characterized by restriction enzyme fingerprinting and by DNA-DNA hybridization with oligonucleotide probes for Salmonella plasmid virulence (Spv) genes. With one exception, the fingerprints of the 38 MDa plasmids studied were homogeneous but there was heterogeneity in the fingerprints of 59 MDa plasmids found in 4 of the type strains. However all 38 MDa and 59 MDa plasmids were related as was a 45 MDa plasmid identified in the type strain of phage type 19. A 3.5 kb fragment homologous to SpvC was conserved in Hind III digests of all 38 MDa and 59 MDa plasmids, and in the related 45 MDa plasmid. In contrast a 65 MDa plasmid found in the type strain of phage type 10 was not related to these three plasmid molecular weight groups and did not carry the SpvC gene.     

Salmonella enteritidis phage types in Germany

In order to monitor the epidemiological situation ofS. enteritidis in Germany, in 1990–91 1138 isolates from more than 180 locations in West Germany were phage typed. 1124 strains (98.8%) from all sources were typeable, belonging to 21 different phage types (PT). PT4 strains were isolated most frequently (70.8%). In addition, PT7, 25, 34 and 8 were of epidemiological relevance with incidences of 7.2 to 4.5%. The comparison of data shows that in Germany, like in other parts of Europe, PT4 predominates. This phage type is, however, infrequent in North America, where PT8 has the highest incidence.     

Competitive exclusion of Salmonella enteritidis by Salmonella gallinarum in poultry

Salmonella Enteritidis emerged as a major egg-associated pathogen in the late 20th century. Epidemiologic data from England, Wales, and the United States indicate that S. Enteritidis filled the ecologic niche vacated by eradication of S. Gallinarum from poultry, leading to an epidemic increase in human infections. We tested this hypothesis by retrospective analysis of epidemiologic surveys in Germany and demonstrated that the number of human S. Enteritidis cases is inversely related to the prevalence of S. Gallinarum in poultry. Mathematical models combining epidemiology with population biology suggest that S. Gallinarum competitively excluded S. Enteritidis from poultry flocks early in the 20th century.     

1起肠炎沙门菌引起学校食源性疾病暴发事件的流行病学调查

目的调查分析1起学校食源性肠炎沙门菌暴发事件的危险因素,提出控制及预防措施。方法采用描述性流行病学方法对该起事件的流行特征进行分析;采用病例对照研究方法进行可疑食物的调查;采集部分病例、厨工肛拭子和环境拭子样本进行病原菌的分离、血清学分型鉴定和脉冲场凝胶电泳分析。结果该起食源性疾病暴发首发病例发病时间为2009年6月9日,末例病例发病时间为6月12日,事件历时4 d,流行曲线提示该次事件符合点源暴发模式。共报告病例61例,均为寄宿生,走读生和教职工均无发病,其中男寄宿生发病12例,罹患率为3.9%（12/309）,女寄宿生发病49例,罹患率为10.7%（49/460）,女生的罹患率明显高于男生（P〈0.01）。病例对照研究结果提示,6月9日早餐的鸡蛋三文治为引起发病的危险食品（OR=21.70,95%CI为8.50～55.50）。采集患者肛拭子25份、食堂厨工肛拭子14份、食堂冰箱和环境拭子11份,分别有19、5、1份样本检出同一血清型的肠炎沙门菌;脉冲场凝胶电泳法分析结果表明该25株肠炎沙门菌分离株具有完全相同的PFGE图谱。结论该事件为1起肠炎沙门菌污染食物引起的食源性疾病暴发事件,可疑中毒食物为6月9日早餐的鸡蛋三文治,卫生监管部门应重视对各类以鸡蛋为原料的食品的卫生监督。     

Iron restriction and the growth of Salmonella enteritidis.

Strains of Salmonella enteritidis were examined for their ability to remove ferric-ions from the iron chelating agents ovotransferrin, Desferal and EDDA. Growth of S. enteritidis phage type (PT) 4 (SE4) in trypticase soy broth containing ovotransferrin resulted in the expression of iron regulated outer membrane proteins (OMPs) of 74, 78 and 81 kDa, and unexpectedly the repression of expression of OMP C. The 38 MDa ''mouse virulence'' plasmid was not required for the expression of the iron-regulated OMPs (IROMPs). SE4 was able to obtain iron bound to the iron chelator Desferal and EDDA without expressing a high-affinity iron uptake system. Strains of S. enteritidis belonging to PTs 7, 8, 13a, 23, 24 and 30 were also able to remove ferric ions from Desferal and EDDA without expressing a high-affinity iron uptake system. We conclude that strains of SE4 possess a high-affinity iron sequestering mechanism that can readily remove iron from ovotransferrin. It is likely that iron limitation, and not iron restriction, is responsible for the bacteriostatic properties of fresh egg whites.