Morphological distinction between different H serotypes of Escherichia coli.

The structure of the flagellar filaments of 50 Escherichia coli strains, each with a different H antigen, was examined. Although the flagella within each strain were structurally identical, there was variability in flagellar surface pattern between strains with differrent H antigens. Investigation of additional strains confirmed that flagella structure was the same in all strains having the same H antigen. In three pairs of strains with cross-reacting H antigens, the antigenic relatedness was associated with identical flagella structure.     

Partial antigenic structure of group H10 flagellins in Escherichia coli and its genetic determination

The study of flagellar antigens classified with serotype H10 has been made in E. coli belonging to different OK-groups. These antigens have been shown to differ in their partial structure. Group H10 antigens have been found to comprise 7 variants, and their partial structure has been determined. The study has shown that antigenic variants of the same type occur in E. coli belonging to different OK-groups and different variants may occur in strains within the same OK-group. The data obtained in the study of the expression of genes, responsible for the synthesis of flagellin, in the system of isogenic strains suggest that differences in the partial structure between the variants of group H10 antigens are linked with differences between the corresponding alleles of the flagellin-specifying gene. The differentiation of these antigens by means of factor-specific antibodies may prove to be of practical importance for solving the problems of the epidemiology and etiology of diseases caused by E. coli having group H10 flagellar antigens.     

Use of factor-H sera for the differentiation of the flagellar antigens of Escherichia coli serological variants

The use of factor sera permitting the differentiation of the variants, described in earlier. works, among the flagellar antigens of E. coli, formally denoted as H2, H4, H7, H10 and H34 in accordance with their official nomenclature, has made it possible to reveal that each of these variants is widely spread among E. coli and occurs in bacteria of different O-groups. Besides, this study has shown the possibility of subdividing a number of formal H: O types into 2 or more serovars on the basis of differences in the factor composition of their antigens. The results obtained in this study suggest that in the process of the evolution of E. coli H-antigen variants differing in their factor composition have been formed as independent varieties; therefore, these variants do not reflect the features characteristic of individual strains, but constitute one of the diagnostic signs of serological classification, i. e. the differentiation of the species into various serovars.     

Different alleles of the flagellin gene hagB in Escherichia coli standard H test strains

Abstract The genes determining flagellar antigen specificities H36, H47 and H53 in the respective E. coli standard H test strains were found to be alleles of the flagellin gene hagB . Until now, only the allele encoding the flagellar antigen H3 has been identified. The chromosomal regions of flagellin genes hagB in E. coli and H2 in Salmonella were non-homologous as these genes integrated at different sites in the E. coli K-12 chromosome and were unable to replace each other. The hagA allele encoding E. coli flagellar antigen H48 was insensitive to the repressor produced by Salmonella gene rhl or by its putative analog in E. coli .     

The production of F41 fimbriae by piglet strains of enterotoxigenic Escherichia coli that lack K88, K99 and 987P fimbriae

The enterotoxigenic Escherichia coli strains 1676, 1706, 1751 and KEC96a, which do not produce fimbrial adhesive antigens of the K88, K99 or 987P antigen type reacted both in vitro and in vivo with antiserum to F41 fimbriae in an indirect immunofluorescent antibody technique. Antiserum used to demonstrate material B, an adhesive antigen thought to mediate the adhesive and mannose-resistant (MR) haemagglutinating properties of E. coli strains 1676, 1706 and 1751, reacted in vitro with an F41+ strain. The antiserum also inhibited the MR haemagglutinating activity of F41 antigen and gave an anionic precipitation line in immunoelectrophoresis experiments with an extract containing F41 antigen. The MR haemagglutinating properties of an antigen extract containing material B from E. coli strain 1706 was neutralized by antiserum to F41 fimbriae and by OK antisera to E. coli strains that produce both F41 and K99 fimbriae. These sera also gave an anionic precipitation line with the MR haemagglutinin from E. coli strain 1706 and the MR haemagglutinin gave a line of identity with F41 in gel diffusion experiments with antiserum to F41 fimbriae. OK antisera to K99+ F41- bacteria and OK antisera to K88+ bacteria and 987P+ bacteria did not react with this haemagglutinin. Transmission electron microscopy on the ileum of newborn gnotobiotic piglets infected with E. coli strain 1706 showed irregular, poorly defined filamentous material surrounding some,though not all, bacteria but regular fimbrial structures were not visible.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phage conversion of the antigens in Escherichiae and Shigellae. 2. Conversion of the somatic antigen in Shigella flexneri with the moderate E. coli 0129 phage]

The authors studied the converting activity of the moderate EF5 phage isolated from the lysogenic E. coli 0129 strain. It was shown that this phage converted the O-antigen with the detection of the type antigen V in the strains of Sh. flexneri of the serological type la and y-variant. The converted cultures contained the type antigen V and were identical by the antigenic properties to one another and the Sh. flexneri of the serological type 5 and E. coli 0129. A conclusion was drawn that phages converting the antigens of Sh. flexneri could be encountered in escherichia and could modify the antigens in Sh. flexneri and escherichia possessing the antigenic factor 3,4.     

Serological variety of flagellar antigen H1 in natural Escherichia coli population

Abstract Variation of the Escherichia coli flagellar antigen H1 was studied among 120 human isolates belonging to more than 25 O:K serovars. Factor-specific antisera were prepared and shown to be useful in the identification of serological subtypes of H1. The three subtypes found were defined as H1abc, H1acd and H1abe. The H1abc corresponded to the standard flagellar antigen H1 present in 84% of all strains. It was found in all O groups except O15, O17 and O83. Eight O15 and two O17 strains studied were of subtype H1abe, while the one O83 strain studied was H1acd. Both subtypes H1abc and H1acd were found among strains within O6:K5, O6:K13 or O-non-typeable:K5 serovars.     

Serological cross-reaction between the lipopolysaccharide O-polysaccharaide antigens of Escherichia coli O157:H7 and strains of Citrobcter freundii and Citrobacter sedlakii

A strain of Citrobacter sedlakii showing serological cross-reaction with Escherichia coli O157 antisera was demonstrated to produce a lipopolysaccharide O-antigen having an identical structure with that of the E. coli O157 O-antigen. A strain of Citrobacter freunndii showing similar cross-reaction with E. coli O157 specific monoclonal antibody was shown to produce a lipopolysaccharide O-antigen composed of a trisaccharide repeating unit having the structure [ 2)-alpha-D Rhap-(1-3)-beta-D-Rhap-(1-4)-beta-D-Glcp-(1-]. This O-antigen differs from that of the E. coli O157 O-antigen and also lacks a component 2-substituted 4-amino-4,6-dideoxy-alpha-D-mannopyranosyl residue implicated as the common epitope in the lipopolysaccharide O-antigens of previously investigated bacterial species showing serological cross-reactivity with E. coli O157 antisera. The C freundii O-antigen presents an interesting example of structural mimicry within a bacterial polysaccharide antigen.     

Structure and serologic properties of O-specific polysaccharide from Citrobacter freundii possessing cross-reactivity with Escherichia coli O157:H7

Citrobacter freundii OCU158 is a serologically cross-reactive strain with Escherichia coli O157:H7. To explore the close relationship between two strains, we have analyzed the chemical structures of O-specific polysaccharides and antigenic properties of lipopolysaccharides (LPSs) of both strains. The structure of O-specific polysaccharides from both strains was found to be identical by chemical and nuclear magnetic resonance analyses, in which D-PerNAc was 4-acetamido-4,6-dideoxy-D-mannose: [-->4)-beta-D-Glc-(1-->3)-alpha-D-PerNAc-(1-->4)-alpha-D-GalNAc-(1 --> 3)-alpha-L-Fuc-(1-->](n). The enzyme immunoassay using LPS derived either from E. coli O157 or from C. freundii could equally detect high levels of serum antibodies against LPS in patients with enterohemorrhagic E. coli (EHEC) O157 infection. Absorption of antibodies in EHEC patient serum by LPS from E. coli O157 or C. freundii, however, showed a difference in the epitopes. This difference was attributable to the epitope specificity of the core region and/or lipid A structure in LPS.     

Cloning of chromosomal DNA encoding the F41 adhesin of enterotoxigenic Escherichia coli and genetic homology between adhesins F41 and K88.

The genetic determinant for production of the adhesive antigen F41 was isolated from a porcine enterotoxigenic Escherichia coli strain by cosmid cloning. The cloned DNA included sequences homologous to those of hybridization probes prepared from the K88 adhesive antigen operon. Transposon insertions which inactivated F41 production mapped to the same region of DNA showing homology with the K88 genes, demonstrating the genetic relatedness of F41 and K88. Hybridization of a K88 gene probe to plasmid and total DNA from the porcine E. coli isolate from which the F41 gene was cloned indicated that F41 is chromosomally encoded by this strain. This observation was extended to other F41-producing animal isolates. A large number of animal E. coli isolates were examined with K88, F41, and K99 gene probes and for mannose-resistant hemagglutination of human group O erythrocytes and K88 and F41 antigen production. All K88 and F41 antigen producers possessed genetic homology with the K88 and F41 gene probes. Most, but not all, F41-producing strains possessed homology to the K99 gene probe, reflecting the previously observed association of F41 and K99 antigen production. In the strains examined, homology with the K99 gene probe was plasmid associated, whereas homology with the F41 gene probe was chromosomal. The K88 antigen-producing strains showed no homology with the K99 probe. A number of strains possessed homology with the K88 and F41 gene probes and were mannose-resistant hemagglutination positive, but did not produce K88 or F41 antigens. This suggests that there are adhesins among animal isolates of E. coli which are genetically related to but antigenically distinct from K88 and F41.     

The structures of Escherichia coli O-polysaccharide antigens

Escherichia coli is usually a non-pathogenic member of the human colonic flora. However, certain strains have acquired virulence factors and may cause a variety of infections in humans and in animals. There are three clinical syndromes caused by E. coli : (i) sepsis/meningitis; (ii) urinary tract infection and (iii) diarrhoea. Furthermore the E. coli causing diarrhoea is divided into different 'pathotypes' depending on the type of disease, i.e. (i) enterotoxigenic; (ii) enteropathogenic; (iii) enteroinvasive; (iv) enterohaemorrhagic; (v) enteroaggregative and (vi) diffusely adherent. The serotyping of E. coli based on the somatic (O), flagellar (H) and capsular polysaccharide antigens (K) is used in epidemiology. The different antigens may be unique for a particular serogroup or antigenic determinants may be shared, resulting in cross-reactions with other serogroups of E. coli or even with other members of the family Enterobacteriacea . To establish the uniqueness of a particular serogroup or to identify the presence of common epitopes, a database of the structures of O-antigenic polysaccharides has been created. The E. coli database (ECODAB) contains structures, nuclear magnetic resonance chemical shifts and to some extent cross-reactivity relationships. All fields are searchable. A ranking is produced based on similarity, which facilitates rapid identification of strains that are difficult to serotype (if known) based on classical agglutinating methods. In addition, results pertinent to the biosynthesis of the repeating units of O-antigens are discussed. The ECODAB is accessible to the scientific community at http://www.casper.organ.su.se/ECODAB/ .     

Assessment of resistance to colicinogenic Escherichia coli by E. coli O157:H7 strains

AIMS: To assess a collection of 96 Escherichia coli O157:H7 strains for their resistance potential against a set of colicinogenic E. coli developed as a probiotic for use in cattle. METHODS AND RESULTS: Escherichia coli O157:H7 strains were screened for colicin production, types of colicins produced, presence of colicin resistance and potential for resistance development. Thirteen of 14 previously characterized colicinogenic E. coli strains were able to inhibit 74 serotype O157:H7 strains. Thirteen E. coli O157:H7 strains were found to be colicinogenic and 11 had colicin D genes. PCR products for colicins B, E-type, Ia/Ib and M were also detected. During in vitro experiments, the ability to develop colicin resistance against single-colicin producing E. coli strains was observed, but rarely against multiple-colicinogenic strains. The ability of serotype O157:H7 strains to acquire colicin plasmids or resistance was not observed during a cattle experiment. CONCLUSIONS: Escherichia coli O157:H7 has the potential to develop single-colicin resistance, but simultaneous resistance against multiple colicins appears to be unlikely. Colicin D is the predominant colicin produced by colicinogenic E. coli O157:H7 strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential for resistance development against colicin-based strategies for E. coli O157:H7 control may be very limited if more than one colicin type is used.     

Polymorphism, duplication, and IS1-mediated rearrangement in the chromosomal his-rfb-gnd region of Escherichia coli strains with group IA and capsular K antigens.

Individual Escherichia coli strains produce several cell surface polysaccharides. In E. coli E69, the his region of the chromosome contains the rfb (serotype O9 lipopolysaccharide O-antigen biosynthesis) and cps (serotype K30 group IA capsular polysaccharide biosynthesis) loci. Polymorphisms in this region of the Escherichia coli chromosome reflect extensive antigenic diversity in the species. Previously, we reported a duplication of the manC-manB genes, encoding enzymes involved in GDP-mannose formation, upstream of rfb in strain E69 (P. Jayaratne et al., J. Bacteriol. 176:3126-3139, 1994). Here we show that one of the manC-manB copies is flanked by IS1 elements, providing a potential mechanism for the gene duplication. Adjacent to manB1 on the IS1-flanked segment is a further open reading frame (ugd), encoding uridine-5'-diphosphoglucose dehydrogenase. The Ugd enzyme is responsible for the production of UDP-glucuronic acid, a precursor required for K30 antigen synthesis. Construction of a chromosomal ugd::Gm(r) insertion mutation demonstrated the essential role for Ugd in the biosynthesis of the K30 antigen and confirmed that there is no additional functional ugd copy in strain E69. PCR amplification and Southern hybridization were used to examine the distribution of IS1 elements and ugd genes in the vicinity of rfb in other E. coli strains, producing different group IA K antigens. The relative order of genes and, where present, IS1 elements was established in these strains. The regions adjacent to rfb in these strains are highly variable in both size and gene order, but in all cases where a ugd homolog was present, it was found near rfb. The presence of IS1 elements in the rfb regions of several of these strains provides a potential mechanism for recombination and deletion events which could contribute to the antigenic diversity seen in surface polysaccharides.     

Monoclonal antibodies for detection of the H7 antigen of Escherichia coli.

Two murine monoclonal antibodies (MAbs) (2B7 and 46E9-9) reactive with the H7 flagellar antigen of Escherichia coli were produced and characterized. A total of 217 E. coli strains (48 O157:H7, 4 O157:NM, 23 O157:non-H7, 22 H7:non-O157, and 120 non-O157:nonH7), 17 Salmonella serovars, and 29 other gram-negative bacteria were used to evaluate the reactivities of the two MAbs by indirect enzyme-linked immunosorbent assay (ELISA). Both MAbs reacted strongly with all E. coli strains possessing the H7 antigen and with H23- and H24-positive E. coli strains. Indirect ELISA MAb specificity was confirmed by inhibition ELISA and by Western blotting (immunoblotting), using partially purified flagellins from E. coli O157:H7 and other E. coli strains. On a Western blot, MAb 46E9-9 was more reactive against H7 flagellin of E. coli O157:H7 than against H7 flagellin of E. coli O1:K1:H7. Competition ELISA suggested that MAbs 2B7 and 46E9-9 reacted with closely related H7 epitopes. When the ELISA reactivities of the MAbs and two commercially available polyclonal anti-H7 antisera were compared, both polyclonal antisera and MAbs reacted strongly with E. coli H7 bacteria. However, the polyclonal antisera cross-reacted strongly both with non-H7 E. coli and with many non-E. coli bacteria. The polyclonal antisera also reacted strongly with H23 and H24 E. coli isolates. The data suggest the need to define serotype-specific epitopes among H7, H23, and H24 E. coli flagella. The anti-H7 MAbs described in this report have the potential to serve as high-quality diagnostic reagents, used either alone or in combination with O157-specific MAbs, to identify or detect E. coli O157:H7 in food products or in human and veterinary clinical specimens.     

Properties of wild-type strains of enterotoxigenic Escherichia coli which produce colonization factor antigen II, and belong to serogroups other than O6

Enterotoxigenic strains of Escherichia coli, which belonged to serogroups other than O6 and produced colonization factor antigen II, usually produced only coli surface antigen 3 (CS3) and gave weak mannose-resistant haemagglutination of bovine erythrocytes. A non-autotransferring plasmid, NTP165, from a strain of E. coli O168. H16 coded for heat-stable enterotoxin, heat-labile enterotoxin and CS antigens. The CS antigens expressed after acquisition of plasmid NTP165 depended on the recipient strain: a biotype A strain of serotype O6. H16 expressed CS1 and CS3; a biotype C strain of serotype O6. H16 expressed CS2 and CS3; strain K12 and strain E19446 of serotype O139. H28 expressed only CS3. An exceptional wild-type strain, E24377, of serotype O139. H28 produced CS1 and CS3 when isolated; a variant of E24377 which had lost the plasmid coding for CS antigens produced both CS1 and CS3 after the introduction of NTP165.     

HIV—1 P24截短体与gp41截短体的融合蛋白在大肠杆菌中的表达、纯化和鉴定

用基因重组技术将截短的HIV－1 p24基因和gp41基因连接成嵌合基因,插入质粒pGEX-4T3,构建成重组表达质粒pGEX-F。将pGEX-F转化大肠杆菌BL21。经IPTG诱导表达,pGEX-F在大肠杆菌BL21中获得了高效表达。融合蛋白P24－gp41经Glutathione-Sepharose4B亲和层析纯化后,用间接ELISA和免疫印迹检测HIV抗体阳性血清和正常人血清,P24－gp41只与HIV抗体阳性血清反应,证明获得的融合蛋白P24－gp41有很强的抗原特异性和免疫反应性,具有较高的应用价值。     

A rapid subtractive immunization method to prepare discriminatory monoclonal antibodies for food E. coli O157:H7 contamination

To detect food E. coli O157:H7 contamination rapidly and accurately, it is essential to prepare high specific monoclonal antibodies (mAbs) against the pathogen. Cyclophosphamide (Cy)-mediated subtractive immunization strategy was performed in mice to generate mAbs that react with E. coli O157:H7, but not with other affiliated bacteria. Specificity of 19 mAbs was evaluated by ELISA and/or dot-immunogold filtration assay (DIGFA). Immunogloubin typing, affinity and binding antigens of 5 selected mAbs were also analysed. MAbs 1D8, 4A7, 5A2 were found to have high reactivity with E. coli O157:H7 and no cross-reactivity with 80 other strains of bacteria including Salmonella sp., Shigella sp., Proteus sp., Yersinia enterocolitica, Staphylococcus aureus, Klebsiella pneumoniae, Citrobacter freundii and other non-E. coli O157:H7 enteric bacteria. Their ascetic titers reached 1:10(6) with E. coli O157:H7 and affinity constants ranged from 1.57 × 10(10) to 2.79 × 10(10) L/mol. The antigens recognized by them were different localized proteins. Furthermore, immune-colloidal gold probe coated with mAb 5A2 could specifically distinguish minced beef contaminated by E. coli O157:H7 from 84 other bacterial contaminations. The Cy-mediated subtractive immunization procedure coupled with hybridoma technology is a rapid and efficient approach to prepare discriminatory mAbs for detection of E. coli O157:H7 contamination in food.     

Comparison of the flagellins from different flagellar morphotypes of Escherichia coli.

The molecular weights of the flagellins of 13 strains of Escherichia coli, each with a different H antigen, were estimated using polyacrylamide gel electrophoresis. In each case only one major polypeptide was demonstrated, although some strains possessed apparently sheathed flagella. Considerable differences in the molecular weight of flagellin accompanied the previously described structural differences between flagella from strains with different H antigens. The relationship between flagellar diameter and the molecular weight of the corresponding flagellins was similar for both unsheathed and apparently sheathed flagella. Crosss-polymerization occurred between seed consisting of fragment of unsheathed flagella and flagellin solution from apparently sheathed flagella and vice versa. Co-polymerization of flagellin from unsheathed flagella and flagellin from apparently sheathed flagella was also demonstrated. These polymerization experiments indicate that the assembly pattern of flagellin molecules is probably the same in all E. coli flagella. The above and other evidence suggests that there is no true sheath, but that the differences in flagellar surface structure between different E. coli flagella are the result of differences in the superficial parts of the flagellin molecules.     

Two genetic arrangements determining flagellar antigen specificities in two diphasic Escherichia coli strains

Abstract Two diphasic Escherichia coli strains, Bi7327-41 and P12b, which spontaneously change their flagellar antigenic characters from H3 to H16, and from H17 to H4, respectively, were investigated. New features of the genetic control of flagellar phase variation in Bi7327-41 and Salmonella were found. Two genes responsible for the alternative flagellar phases H17 and H4 were demonstrated in P12b. They differed from hagA (H16) and hagB (H3), the two flagellin genes of Bi7327-41, in not being alleles of hagB (H3) or sensitive to the hagA (H16)-specific repressor.     

Morphological description of surface structures on strain B41 of bovine enterotoxigenic Escherichia coli bearing both K99 and F41 antigens

In order to describe morphologically the structures on the cell surface of bovine enterotoxigenic Escherichia coli, variants of reference strain B41 (K99+F41+) either negative for K99 and positive for F41 antigens (variants B41A, B41*C), or phenotypically negative for both antigens (variants B41B1, B41B2, B41*CB), and a transconjugant harbouring the K99 plasmid and expressing the K99 adhesin [transconjugant B41 x H510a:H510(2)] were examined by transmission electron microscopy using negative staining. Several negative staining procedures were tested for strain B41 and variant B41A: direct harvesting of strains into ammonium molybdate (2%, w/v), with bacitracin (50 micrograms ml-1) as wetting agent, gave the best results. Three morphologically distinct structures on the cell surface could be identified in cultures grown on Minca medium. Firstly, thin, filamentous, flexible fibrillar structures, presenting a helical structure and a mean diameter of approximately 3 nm, were recognized as K99 fimbriae, since they were present on strain B41 and on transconjugant H510(2), but not on K99-negative variants nor on the recipient strain H510a. Secondly, coil-like structures with a diameter of about 17-20 nm were observed on strain B41 and on variants B41A and B41*C. These structures appeared to consist of two or more curled filaments (diameter 3 nm) joined to coil on themselves into dense spirals. They were very rare in variants B41B1 and B41B2 and were absent on variant B41*CB and on a transconjugant B41* x B41*CB, which had re-acquired the K99 plasmid and which again exhibited K99 fimbriae. Strains B41 and variant B41A gown at 37 degrees C for 24 h on sheep-blood agar exhibited coiled structures like those seen on Minca medium. In contrast, after growth at 18 degrees C for 48 h (which inhibits the synthesis of F41 antigen), coiled structures were no longer expressed on the cell surface of strain B41 and variants B41A and B41*C. Thus the presence of coiled structures correlated with the expression of F41 antigen in strains and variants, which suggests that F41 had a coiled morphology. Finally, straight fimbriae (diameter 6.5-7 nm) were observed on the cell surface of every strain and variant. Their expression on the cell surface was enhanced by several subcultures in th e static broth, and it was inhibited by subculture on agar, but not by culture at 18 degrees C after serial subcultures in static broth. These facts indicated that the straight fimbriae could be common fimbriae, and excluded their being F41 structures.