Interrelationships between strains of Salmonella enteritidis belonging to phage types 4, 7, 7a, 8, 13, 13a, 23, 24 and 30

Salmonella enteritidis strain P278849 expressed long-chain lipopolysaccharide (LPS, termed 'smooth'), carried plasmids of 38, 34 (pDEP 44, incompatibility group N, R-type AS), 2.0 and 1 MDa, and belonged to phage type (PT) 23. Introduction of pDEP 44 into a smooth strain of Salm. enteritidis PT 4 produced a smooth strain of Salm. enteritidis of PT 24. Transfer of this plasmid into a strain of PT 8 also resulted in formation of a smooth strain of Salm. enteritidis of PT 24. Moving pDEP 44 into strains of Salm. enteritidis of PTs 7 or 7a which did not express LPS (termed 'rough') resulted in rough strains of PT 23. In contrast, transfer of this plasmid into a smooth strain of Salm. enteritidis PT 7a resulted in a smooth strain of PT 23. Introduction of pDEP 44 into strains of Salm. enteritidis of PT 13 or PT 13a did not change the phage type, whereas transferring the plasmid into strains of PT 30 caused strains to become resistant to lysis by the typing phages and therefore untypable. The possibility of strains of Salm. enteritidis of PT 8 being the progenitors of strains of Salm. enteritidis of PT 24 must now be considered when investigating the epidemiology of Salm. enteritidis of PT 24 infections in areas where Salm. enteritidis PT 8 is common.     

Plasmid characterization and pulsed-field electrophoretic analysis demonstrate that ampicillin-resistant strains of Salmonella enteritidis phage type 6a are derived from Salm. enteritidis phage type 4

Plasmid incompatibility studies have demonstrated that strains of Salmonella enteritidis phage type (PT) 6a resistant to ampicillin possess a 36 megadalton incompatibility group (Inc) X plasmid coding for resistance to ampicillin which is capable of converting strains of Salm. enteritidis belonging to PTs 1 and 4 to PT 6a, and PT 8 to PT 13. However, pulsed-field gel electrophoresis (PFGE) has demonstrated that all clinical isolates of PT 6a have a characteristic Xba I pulsed-field profile which is distinct from that of PT 1 and which can only be differentiated from that of PT 4 by the presence of plasmid-associated fragments of less than 45 kb. It is concluded that ampicillin-resistant strains of Salm. enteritidis PT 6a are derived from strains of Salm. enteritidis PT 4 by acquisition of an Inc X ampicillin resistance plasmid.     

Virulence studies of Salmonella enteritidis phage types

Salmonella enteritidis phage types (PTs) 8, 13a and 24 could be distinguished by their virulence for BALB/c mice, their plasmid content and plasmid fingerprint. Virulent strains expressed long-chain lipopolysaccharide and carried a 38 MDa plasmid indistinguishable from that in Salm. enteritidis PT 4. Avirulent strains were smooth but did not carry the 38 MDa plasmid. Possession of antibiotic resistance factors by some strains of Salm. enteritidis PT 24 did not contribute to the virulence of their host strains.     

Antibodies to lipopolysaccharide and outer membrane proteins of Salmonella enteritidis PT4 are not involved in protection from experimental infection

BALB/c and Schofield mice were inoculated with formalin-killed bacteria prepared from strains of Salmonella enteritidis belonging to phage type (PT) 4 and carrying a 38 MDa plasmid and expressing long-chain lipopolysaccharide, or strains without a 38 MDa plasmid or lacking the ability to express lipopolysaccharide. Vaccinated mice were challenged with viable bacteria belonging to a virulent strain of S. enteritidis (PT4). Mice surviving this viable challenge were examined for a humoral antibody response to membrane antigens of S. enteritidis (PT4) that might relate to the possession of a given virulence property. BALB/c mice immunized with any of the test antigens were found to be immune to S. enteritidis (PT4), and this immunity was protective. Serum antibodies, of the IgG class, were detected to OmpA and a minor outer membrane protein (OMP) of 31 kDa. Schofield mice also raised IgG antibodies to these outer membrane proteins; however, non-immunized mice of this strain were resistant to infection. The virulence of S. enteritidis (PT4) was also tested using mice belonging to strains B10D2 (new), Biozzi (high), Biozzi (low), C3HeJ, B10ITYR and C57/L.     

The spread and antibiotic resistance of Salmonella enterica serotype typhimurium DT104 in Hungary

Comparison of phage types (PTs) determined by Felix and Callow's and Anderson's methods was performed testing 99 human strains of S. enterica serotype Typhimurium (S. typhimurium) isolated in Hungary. PT2 and PT2c--according to Felix-Callow--corresponded with Anderson's DT104 in case of 39 strains out of 40. Among 59 isolates belonging to other Felix-Callow's PTs only one strain was found which was DT 104. Similar unambiguous equalities could not be established between any other PTs comparing the two methods. The PTs of 17,877 human strains isolated between 1988 and 1999 were determined using Felix-Callow's method. On the basis of the above equality the emergence of DT104 could be followed retrospectively by means of the rate of PT2 and PT2c. The increase of DT104 began already in 1989, emerging first PT2c then PT2. It predominated since 1991 and it reached its maximum (78.3%) in 1999. The incidence of multiresistance among one of the groups of DT104 strains (Felix-Callow's PT2) was significantly higher in 1998 than the average of non-DT104 strains. The predominant R-type was ACST.     

Genotypic characterization and prevalence of virulence factors among Canadian Escherichia coli O157:H7 strains

In this study, the association between genotypic and selected phenotypic characteristics was examined in a collection of Canadian Escherichia coli O157:H7 strains isolated from humans and cattle in the provinces of Alberta, Ontario, Saskatchewan, and Quebec. In a subset of 69 strains selected on the basis of specific phage types (PTs), a strong correlation between the lineage-specific polymorphism assay (LSPA6) genotype and PT was observed with all strains of PTs 4, 14, 21, 31, 33, and 87 belonging to the LSPA6 lineage I (LSPA6-LI) genotype, while those of PTs 23, 45, 67, and 74 belonged to LSPA6 lineage II (LSPA6-LII) genotypes. This correlation was maintained when additional strains of each PT were tested. E. coli O157:H7 strains with the LSPA6-LI genotype were much more common in the collection than were the LSPA6-LII or lineage I/II (LSPA6-LI/II)-related genotypes (82.6, 11.2, and 5.8%, respectively). Of the strains tested, proportionately more LSPA6-LI than LSPA6-LII genotype strains were isolated from humans (52.7% versus 19.7%) than from cattle (47.8% versus 80.2%). In addition, 96.7% of the LSPA6-LII strains carried the stx(2c) variant gene, while only 50.0% of LSPA6-LI/II and 2.7% of LSPA6-LI strains carried this gene. LSPA6-LII strains were also significantly more likely to possess the colicin D gene, cda (50.8% versus 23.2%), and have combined resistance to streptomycin, sulfisoxazole, and tetracycline (72.1% versus 0.9%) than were LSPA6-LI strains. The LSPA6 genotype- and PT-related characteristics identified may be important markers of specific ecotypes of E. coli O157:H7 that have unique epidemiological and virulence characteristics.     

Comparative study of the effectiveness of HBcAg presentation to the immune system using attenuated Salmonella strains, serovars S.enteritidis and S.typhimurium

In this work the results of obtaining HBcAg-producing attenuated Salmonella strains, serovars S. enteritidis and S. typhimurium, and their comparative study is presented. As revealed in this study, attenuated S. enteritidis strain E-23 and S. typhimurium strain T-10, producing HBcAg, induce cell-mediated and humoral immune response to HBcAg after injected into anovals. After injection S. typhimurium strain T-10 induces a much higher titer of specific antibodies than S. enteritidis strain E-23. The level of specific antibodies induced by recombinant HBcAg seems to correlate with the capacity of salmonellae for survival inside macroorganisms.     

Heat resistance and growth of Salmonella enteritidis, Listeria monocytogenes and Aeromonas hydrophila in whole liquid egg

Salmonella enteritidis ATCC,13067, Listeria monocytogenes ATCC,19116 and Aeromonas hydrophila ATCC,7965 strains were evaluated for growth and thermal resistance in liquid whole egg (LWE). Each strain grew well in LWE at temperatures between 4 and 30 degrees C, except S. enteritidis which grew weakly at 4 and 10 degrees C. Maximum populations for each strain increased with increasing growth temperature. The thermal destruction of each strain was determined in six liquid products. The egg products used were LWE, LWE with 5, 10 and 15% NaCl and LWE with 5 and 10% sucrose. L. monocytogenes tended to be more heat resistant than S. enteritidis and A. hydrophila. The highest kill rates were noted in LWE, while survival was best in those products supplemented with NaCl. Radiation D10 values of strains in LWE were 0.18, 0.39 and 0.49 kGy for A. hydrophila, S. enteritidis and L. monocytogenes, respectively.     

Siderophore production by Salmonella species isolated from different sources

A total of 230 Salmonella strains were screened for enterobactin and aerobactin production, sensitivity to bacteriocins and resistance to antibiotics. All the isolates produced the phenolate siderophore enterobactin. Amongst these, 74 strains, most belonging to S. enteritidis, were sensitive to colicin B. Only 26 isolates, all belonging to S. wien, produced an additional iron chelator, i.e. the siderophore aerobactin, and 22 out of these were sensitive to cloacin DF13. Analysis of iron repressible outer membrane proteins and plasmid profiles in S. wien strains showed that the expression of a 74-kDa iron-repressible outer membrane protein and the presence of large plasmids were associated with multiple antibiotic resistance, aerobactin production and sensitivity to cloacin DF13. The incidence of aerobactin-producing strains among S. wien isolates was higher during years 1974-1985; the epidemiological implications of these results are discussed.     

Unusual expression of lipopolysaccharide by strains of Salmonella enteritidis phage type 30

An investigation of 83 strains of Salmonella enteritidis phage type 30 showed that these bacteria were unusual in expressing either trace amounts of, or no, lipopolysaccharide (LPS). Regardless of whether strains expressed LPS or not, or carried a 38 MDa mouse virulence' plasmid, these strains were avirulent for BALB/c mice.     

Virulent strains of Salmonella enteritidis disrupt the epithelial barrier of Caco-2 and HEp-2 cells

To confirm the existence in nature of Salmonella enteritidis strains of different degrees of virulence and to elucidate the mechanisms underlying the effects of such strains on the epithelial barrier function, the consequences of infection of Caco-2 cells and HEp-2 cells with 15 S. enteritidis strains in a chicken infection model were examined. The more virulent strains of S. enteritidis, which are biofilm producers in adherence test medium, were able to disrupt HEp-2 and Caco-2 monolayers, as shown by transmonolayer electrical resistance and lactate dehydrogenase activity. In contrast, the low-virulence strains of S. enteritidis, which do not produce biofilms in adherence test medium, had no effect on the same cells. An avirulent rough mutant of Salmonella minnesota exhibited a pattern of behaviour similar to that of the low virulence strains of S. enteritidis, whilst a clinical Salmonella typhi strain caused rapid injury to the monolayers. The effect of supernatants of Salmonella cultures in adherence test medium on the integrity of Caco-2 cell monolayers indicated that the high-virulence S. enteritidis strains, but not the low-virulence strains, release a soluble factor when incubated under optimum biofilm-forming conditions, which enables the disruption of the integrity of Caco-2 monolayers.     

Conversion of Salmonella enteritidis phage type 4 to phage type 7 involves loss of lipopolysaccharide with concomitant loss of virulence

Three strains of Salmonella enteritidis phage type 4 (PT4) and 33 strains of S. enteritidis phage type 7 (PT7) were examined for the ability to produce lipopolysaccharide (LPS) and for plasmid carriage. The LPS of all strains of PT4 gave a typical 'ladder' pattern by SDS-PAGE and silver staining, and on serotyping these strains were shown to express the O-antigens 9, 12. In contrast, strains of PT7 did not express long-chain LPS and were autoagglutinable. All strains of PT4 and the majority of strains of PT7 carried a single plasmid of 38 MDa, indistinguishable when characterised by restriction endonuclease fragmentation analysis. Epidemiological and experimental observations have demonstrated a relationship between strains of S. enteritidis PT4 and PT7, and our results, using mice, show that the loss of ability of strains of PT4 to snythesise LPS is responsible for the conversion of highly virulent strains of PT4 to avirulent strains of PT7. From epidemiological data of human infections in England and Wales, we suggest that strains of S. enteritidis PT7 may be less virulent for humans.     

Plasmid profile typing provides a method for the differentiation of strains of Salmonella enteritidis phage type 4 isolated in Turkey

Five phage types have been identified in 38 strains of Salmonella enteritidis isolated in Turkey in the 20-month period June 1992-January 1994. Strains belonging to phage type 4 predominated. Within phage type 4, plasmid profile typing has proved a useful method of strain discrimination and has confirmed the identity of a putative outbreak involving canteen workers in an industrial complex.     

Analysis of Salmonella enteritidis strains isolated from food-poisoning cases in Taiwan by pulsed field gel electrophoresis, plasmid profile and phage typing

AIMS: To establish the molecular typing data for Salmonella enteritidis due to its increasing role in Salmonella infections in Taiwan. METHODS AND RESULTS: Sixty-three Salm. enteritidis strains isolated from related and unrelated patients suffering from food-borne poisoning during 1991-97 were collected and subjected to pulsed field gel electrophoresis (PFGE), plasmid analysis and phage typing. For PFGE, XbaI, SpeI and NotI restriction enzymes were used for chromosomal DNA digestion. The results showed that, for these 63 Salmonella strains, 10 PFGE pattern combinations were found. Of these, pattern X3 S3 N3 was the major subtype, since 46 strains isolated from different locations at different times during 1991-97 showed this PFGE pattern. Plasmid analysis showed only three plasmid profiles and phage typing showed that most of the Salmonella strains were of the phage type PT4. CONCLUSION: Most of the Salm. enteritidis strains circulating in Taiwan are of very similar genetic types or are highly related and that strains of PFGE pattern X3 S3 N3 are the prevalent and recirculating strains of Salm. enteritidis which caused food-poisoning cases in Taiwan in 1991-97. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides information that in Salmonella infection, certain subtypes of Salm. enteritidis should be scrutinized.     

Inhibition of pathogenic Salmonella enteritidis growth mediated by Escherichia coli microcin J25 producing strains

For the first time, microcin-producing strains showing inhibitory activities against enteropathogen Salmonella enteritidis were isolated from poultry intestinal contents. Among the numerous strains isolated, two strains of Escherichia coli, named J02 and J03, showing the greatest activities against S. enteritidis, were studied. Biochemical tests and purification identified the main antagonist compound produced as microcin J25. In order to evaluate the protective potential of E. coli J02 and J03 against S. enteritidis infection, the ability of these strains to inhibit growth of S. enteritidis was investigated in mixed culture. A strong antagonist activity was obtained with a preculture phase of the active strain in minimal medium before incubation with S. enteritidis. In a bioreactor experiment simulating the chicken gastric and intestinal tract environment, a mixture of the two strains E. coli J02 and J03, provided an enhanced inhibitory effect. Microcinogenic strain activities were not affected by bile, pancreatic enzymes addition, or acidic conditions. These results suggest the relevant role of microcin-producing microorganisms in microbial intestinal ecology. To conclude, this study shows that microcin J25 strains could exert a beneficial protective effect against S. enteritidis growth in situ.     

Stability of plasmids in five strains of Salmonella maintained in stab culture at different temperatures

Four strains of Salmonella berta and one of Salm. enteritidis were stored as stab cultures in sugar-free agar at 5°, 22° and 30°C and in 15% glycerol at—80°C. The stability of the plasmid profiles in each of the strains was monitored over a period of 2·5 years.
Plasmid profiles were stable in all strains stored at—80°C, and only six of 450 colonies examined from strains kept in sugar-free agar at 5°C had lost plasmid molecules. Seventy of 440 colonies from stab cultures that were kept at 22°C, and 71 of 440 colonies at 30°C showed changed plasmid profiles. The total number of plasmids lost increased with time, and occasionally, more than one plasmid molecule was lost in the same strain.
The virulence associated plasmid of Salm. enteritidis was remarkably stable as it was maintained in all colonies examined at all temperatures investigated. Likewise, no change in Sma I restriction profile was observed in this plasmid molecule at any temperature.     

Expression of SEF17 fimbriae by Salmonella enteritidis

M. DIBB-FULLER, E. ALLEN-VERCOE, M. J. WOODWARD AND C. J. THORNS. 1997. Specific immunological reagents were used to investigate the expression of SEF17 fimbriae by cultured strains of Salmonella enteritidis . Most strains of Salm. enteritidis tested expressed SEF17 when cultured at temperatures of 18–30°C. However, two wild-type strains produced SEF17 when also grown at 37 °C and 42 °C. Colonization factor antigen agar was the optimum medium for SEF17 expression, whereas Drigalski and Sensitest agars poorly supported SEF17 production. Very fine fimbriae produced by a strain of Salm. typhimurium were specifically and strongly labelled by SEF17 monoclonal and polyclonal antibodies, indicating considerable antigenic conservation between the two. Curli fimbriae from Escherichia coli were similarly labelled. The production of these fimbriae corellated with the binding of fibronectin by the organism. Congo red binding by cultured bacteria was not a reliable criterion for the expression of SEF17 fimbriae.     

Contribution of capsular and clonal types and beta-lactam resistance to the severity of experimental pneumococcal meningitis

We used a rabbit model to assess the effects of capsular serotype, genetic background and beta-lactam resistance on the course and severity of experimental meningitis. Meningitis was induced by five pneumococcal strains belonging to five different clones with known invasive potential: two serotype 3 strains (ST260(3) and Netherlands(3)-31 clones) and three serotype 23F strains with different beta-lactam susceptibility patterns (Spain(23F)-1 clone, Tennessee(23F)-4 clone and a double locus variant of the Tennessee(23F)-4 clone). Major differences in secondary bacteremia and mortality rates were observed between serotypes 3 and 23F, as were divergences in the CSF lactate, protein and lipoteichoic-teichoic acid concentrations. Minor differences in the CSF-induced inflammatory response were found among strains belonging to the same serotype. Our results suggest that capsular serotype might be the main factor determining the course and severity of pneumococcal meningitis and genetic background contributes to a lesser extent. The acquisition of beta-lactam resistance does not reduce the virulence of the invasive clones. Since five strains belonging to two serotypes were studied, our findings have to be confirmed with other pneumococcal serotypes.     

大连市两种来源的副溶血性弧菌分子分型

目的 分析食品来源、患者来源及2种来源的副溶血性弧菌之间的PFGE图谱的关系,从分子流行病学角度探讨2种来源的副溶血性弧菌的关联.方法 收集患者和食品2种来源的副溶血性弧菌178株,经限制性内切酶SfiI酶切,用脉冲场凝胶电泳方法进行电泳,凝胶成像仪获得电泳图谱,利用BioNumerics软件对图谱进行聚类分析.结果 ...     

Analysis of whole-cell fatty acid profiles of verotoxigenic Escherichia coli and Salmonella enteritidis with the microbial identification system.

Differentiation of strains within bacterial species, based on gas chromatographic analysis of whole-cell fatty acid profiles, was assessed with 115 strains of verotoxigenic Escherichia coli and 315 strains of Salmonella enteritidis. Fatty acid-based subgroups within each of the two species were generated. Variability of fatty acid profiles observed in repeat preparations from the same strain approached that observed between subgroups, limiting the usefulness of using fatty acid profiles to subgroup verotoxigenic E. coli and S. enteritidis strains.