Serotyping of O-(lipopolysaccharide) and H-(flagellar) antigens is a wideley used method for identification of pathogenic strains and clones of Escherichia coli. At present, 176 O- and 53 H-antigens are described for E. coli which occur in different combinations in the strains. The flagellar antigen H4 is widely present in E. coli strains of different O-serotypes and pathotypes and we have investigated the genetic relationship between H4 encoding fliC genes by PCR, nucleotide sequencing and expression studies.
The complete nucleotide sequence of fliC genes present in E. coli reference strains U9-41 (O2:K1:H4) and P12b (O15:H17) was determined and both were found 99.3% (1043 of 1050 nucleotides) identical in their coding sequence. A PCR/RFLP protocol was developed for typing of fliC-H4 strains and 88 E. coli strains reacting with H4 antiserum were investigated. Nucleotide sequencing of complete fliC genes of six E. coli strains which were selected based on serum agglutination titers, fliC-PCR genotyping and reference data revealed 96.6 to 100% identity on the amino acid level. The functional expression of flagellin encoded by fliC-H4 from strain U9-41 and from our strain P12b which is an H4 expressing variant type was investigated in the E. coli K-12 strain JM109 which encodes flagellar type H48. The fliC recombinant plasmid carrying JM109 strains reacted with both H4 and H48 specific antisera whereas JM109 reacted only with the H48 antiserum. By immunoelectron microscopy, we could show that the flagella made by the fliC-H4 recombinant plasmid carrying strain are constituted of H48 and H4 flagellins which are co-assembled into functional flagella.
The flagellar serotype H4 is encoded by closely related fliC genes present in serologically different types of E. coli strainswhich were isolated at different time periods and geographical locations. Our expression studies show for the first time, that flagellins of different molecular weigth are functionally expressed and coassembled in the same flagellar filament in E. coli.
The objectives of this study were: (i) to investigate the prevalence of Escherichia coli producing F5 (K99), F41, or F165 fimbriae and STa enterotoxin; (ii) to determine serum antibody levels against these fimbriae; (iii) and to examine the association between bacteriological and serological results and the presence of diarrhea, in beef calves from northwestern Quebec. A total of 373 live three to four week old calves and 27 dead calves were sampled between January and March 1991. No isolates positive for F5 were detected in live calves, and only one E. coli producing STa and F41 was isolated. Escherichia coli producing F41-like surface antigens or F165 fimbriae were isolated from 17.43% and 5.63% of live calves, respectively. Antibodies against F5, F41 and F165 were low. Escherichia coli isolates positive for F41-like surface antigen were most often observed in calves born between January and March. No association was found between bacteriological and serological findings, nor between these findings and diarrhea. Calves born from dams vaccinated against E. coli had higher median antibody levels than those born from unvaccinated dams. No E. coli positive for F5 or F41 fimbriae were isolated from dead calves. Escherichia coli with F41-like surface antigen or F165 were found in 55.56% and 11.11% of ileal samples; 4% and 16% of cecal samples, and 0% and 7.4% of colon samples, respectively. Escherichia coli positive for F41-like surface antigen were detected significantly more frequently in the ileum (chi (2)2df = 31.01, p < 0.001).
P fimbriae of 37 uropathogenic Escherichia coli O1:K1, O7:K1, O22, O75, rough:K1, and nontypable strains were characterized by immunoprecipitation with 14 fimbria-specific rabbit antisera. The fimbrial composition of these strains, as reflected by the apparent molecular weights of the fimbrial peptides, was correlated with the O serogroup of the strains, but serological cross-reactivity of P fimbriae of different E. coli serogroups was frequently observed. The genetic clonal relationships of the strains were analyzed by determining the electrophoretic types, based on 18 chromosomally encoded enzymes. Among the O1:K1 strains, the same P-fimbrial variants occurred on strains that were either closely related or very distinct in their electrophoretic types, indicating that the P fimbriae have evolved in association with the O and K antigens. In contrast, certain O7:K1 and R:K1 strains as well as some O22 and O75 strains were genotypically identical and shared similar P-fimbrial variants, which differed serologically from those of other E. coli serogroups. Our results show that, despite the structural variability seen in electrophoretic analysis of P fimbriae of different serogroups, many P-fimbrial variants share common antigenic determinants that are recognized by rabbit antisera. Based on immunoprecipitation analyses, three anti-P-fimbria sera have now been identified that react with P fimbriae of 82 of 84 uropathogenic E. coli strains characterized in Finland.
A portion of a cDNA encoding a 35-kDa antigen from Toxoplasma gondii was cloned into the CKS expression vector and expressed in Escherichia coli. By using the enzyme-linked immunosorbent assay (ELISA), the recombinant protein (rP35 antigen) was examined for reactivity with immunoglobulin G (IgG) antibodies in the sera of pregnant women. Of these women, 41 had a toxoplasma serologic profile suggestive of recently acquired T. gondii infection (Sabin-Feldman dye test [DT] titers from 1:256 to 1:32,000, positive IgM ELISA titers from 2.3 to 9.7, positive IgA ELISA from 1 to >28, and acute patterns in the differential agglutination [AC/HS] test) (group I), and 50 women had a toxoplasma serologic profile suggestive of infection acquired in the distant past (low DT titers from 1:16 to 1:512, negative IgM ELISA titers from 0 to 0.8, and chronic patterns in the AC/HS test) (group II). The classification of acute or chronic profile was based on the individual's clinical history as well as the combination of the results of the toxoplasma serological profile. An additional group (group III) was composed of sera from 50 women who were seronegative for T. gondii antibodies in the DT. The results revealed that whereas 85.3% of women in group I had IgG antibodies that reacted with the rP35 antigen, only 8% of women in group II had IgG antibodies that reacted with the same antigen. In immunoblots, the rP35 antigen was recognized by IgG antibodies in a pool of sera from individuals with a toxoplasma serologic profile compatible with acute infection but not in a pool of sera from individuals with a serologic profile characteristic of a chronic infection. These results reveal that IgG antibodies against the P35 antigen are produced during the acute stage of the infection but are uncommon in the latent or chronic phase of the infection. Thus, the rP35 antigen may be a useful serologic marker to differentiate between recently acquired infection and that acquired in the more distant past.
We cloned and expressed in Escherichia coli a gene encoding an 18-kDa outer membrane protein (Omp18) from Campylobacter jejuni ATCC 29428. The nucleotide sequence of the gene encoding Omp18 was determined, and an open reading frame of 165 amino acids was revealed. The amino acid sequence had the typical features of a leader sequence and a signal peptidase II cleavage site at the N-terminal part of Omp18. Moreover, the sequence had a high degree of similarity to the peptidoglycan-associated outer membrane lipoprotein P6 of Haemophilus influenzae and the peptidoglycan-associated lipoprotein PAL of E. coli. Southern blot analysis in which the cloned gene was used as a probe revealed genes similar to that encoding Omp18 in all species of the thermophilic group of campylobacters as well as Campylobacter sputorum. All campylobacters tested expressed a protein with a molecular mass identical to that of Omp18. The protein reacted immunologically with polyclonal antibodies directed against Omp18 from C. jejuni. PCR amplification of the gene encoding Omp18 with specific primers and subsequent restriction enzyme analysis of the amplified DNA fragments showed that the gene for Omp18 is highly conserved in C. jejuni strains isolated from humans, dogs, cats, calves, and chickens but is different in other Campylobacter species. In order to obtain pure recombinant Omp18 protein for serological assays, the cloned gene for Omp18 was genetically modified by replacing the signal sequence with a DNA segment encoding six adjacent histidine residues. Expression of this construct in E. coli allowed purification of the modified protein (Omp18-6xHis) by metal chelation chromatography. Sera from patients with past C. jejuni infection reacted positively with Omp18-6xHis, while sera from healthy blood donors showed no reaction with this antigen. Omp18, which is an outer membrane protein belonging to the family of PALs is well conserved in C. jejuni and is highly immunogenic. It is therefore a good candidate as an antigen for the serological diagnosis of past C. jejuni infections.
A hybrid protein consisting of the variable region of the Borrelia burgdorferi flagellin (an 18-kDa fragment) and a 59-kDa fragment (lacking the N-terminal part) of the 83-kDa protein has been constructed by genetic engineering. It was expressed as a nonfusion protein of an apparent molecular weight of 77,000 in Escherichia coli. The suitability of this new antigen for the diagnosis of Lyme disease was tested by immunoblotting; for comparison, the recombinant variable region of the flagellin, the 18-kDa fragment (p18), and the whole recombinant 83-kDa protein (p83), both expressed in E. coli, were used. A total of 120 serum samples from various stages of Lyme disease, which were positive in two serological assays, a passive hemagglutination assay and an indirect immunofluorescence assay, were tested. By indirect immunofluorescence, 74 samples were positive for immunoglobulin G (IgG) antibodies and 72 were positive for IgM antibodies. Of these serum samples, 69 of 74 (93%) contained IgG antibodies against p18 and/or p83, and IgG antibodies were detected by the hybrid protein in 67 (90%) samples. IgM antibodies against p18 and/or p83 were detected in 60 of 72 (83%) serum samples, and 57 (79%) serum samples were reactive with the hybrid protein. Twenty serum samples of patients with a history of syphilis and 40 serum samples, negative in routine B. burgdorferi serology, were tested as controls. The hybrid protein, made up of specific epitopes of an early (p18) and late (p83) antigen, is recognized by almost the same number of patient serum samples as the individual antigens.
Serotyping Escherichia coli is a cumbersome and complex procedure due to the existence of large numbers of O- and H-antigen types. It can also be unreliable, as many Shiga toxin-producing E. coli (STEC) strains isolated from fresh produce cannot be typed by serology or have only partial serotypes. The FDA E. coli identification (FDA-ECID) microarray, designed for characterizing pathogenic E. coli, contains a molecular serotyping component, which was evaluated here for its efficacy. Analysis of a panel of 75 reference E. coli strains showed that the array correctly identified the O and H types in 97% and 98% of the strains, respectively. Comparative analysis of 73 produce STEC strains showed that serology and the array identified 37% and 50% of the O types, respectively, and that the array was able to identify 16 strains that could not be O serotyped. Furthermore, the array identified the H types of 97% of the produce STEC strains compared to 65% by serology, including six strains that were mistyped by serology. These results show that the array is an effective alternative to serology in serotyping environmental E. coli isolates.
Kunin, Calvin M. (University of Virginia, Charlottesville) and Mary V. Beard. Serological studies of O antigens of Escherichia coli by means of the hemagglutination test. J. Bacteriol. 85:541–548. 1963.—The serological interrelationships among most of the known O antigens of Escherichia coli were studied by the hemagglutination test. Good agreement with the bacterial agglutination test was found with the major antigens, but cross reactions among groups were much more limited with the hemagglutination test. Heterogenetic cross reactions with many Enterobacteriaceae species were observed with rabbit antisera to E. coli O14, O56, O124, and O144. This effect tended to elevate antibody titers observed in human serum against almost all O antigen groups, but could not by itself account for the wide diversity of antibodies to them. E. coli antibodies were localized in human γ-globulin, but were present in the β-globulin fractions of a number of domestic animals. Rabbits differed from other animals studied in that antibodies to E. coli were rarely found in their sera; this was attributed in part to the low density of E. coli populations in this animal. The hemagglutination test may be used in identification of unknown O antigens, but does not have special merit over the bacterial agglutination test; it does not further characterize rough or untypable strains other than by demonstrating that they also possess heterogenetic antigens.
Serum immunoglobulin G antibodies to purified heat-labile enterotoxin (LT) from human (LTh) and porcine (LTp) Escherichia coli strains and cholera enterotoxin (CT) were measured by an enzyme-linked immunosorbent assay. Sera from patients with LTh E. coli infection showed a prominent response with LTh, an intermediate response with LTp, and a meager response with CT. Of 47 persons with clinical LTh-producing E. coli (herein shortened to LTh E. coli) infections, significant rises in antitoxin were detected against LTh in 36 (77%), against LTp in 30 (64%), and against CT in only 13 (28%) patients; seroconversions also occurred in 11 of 14 (79%) patients with subclinical LTh E. coli infections. In North Americans with experimental LTh E. coli infection, anti-Lth did not remain at high levels for more than 3 months. Persons with cholera manifested antitoxin responses that were similarly potent against all three toxin antigens; in fact, net optical density values were often slightly higher against LTh than against CT. The ratio of CT/LTh ELISA net optical density in convalescent sera proved to be a sensitive means to differentiate LT E. coli from cholera infection. All 11 cholera patients tested had CT/LTh ratios of greater than 0.70, whereas in only 1 of 47 LTh E. coli infections did the ratio exceed that value (it was 0.71) (P less than 0.0000000001). In single serum specimens, a net optical density of greater than or equal to 0.30 against LTh was shown to be a useful cutoff in screening sera for recent LTh E. coli or past cholera infection. The CT/LTh ratio was then used to differentiate definitively. Sera from healthy 3- to 5-year -olds and 15- to 19-year-olds in Maryland, Chile, and Bangladesh were tested against LTh and CT. The serological results fit known epidemiological observations. (i) LTh infections are rare in the United States (only 2 of 60 sera had LTh net optical density values of >/= 0.30. (ii) In contrast, evidence of recent LTh E. coli infections was very common in Chilean (69%) and Bangladeshi (57%) 3- to 5-year-olds and not uncommon in 15- to 19-year-olds (38 and 31%, respectively) in those countries. (iii) Only Bangladeshi sera showed serological evidence of cholera infections (CT/LTh ratios of > 0.70). The immunoglobulin G enzyme-linked immunosorbent assay measuring antibodies to purified LTh and CT represents a practical and effective tool for the serological study of LTh E. coli and cholera diarrheal infections.
Flagellar type H8 is associated with many strains of pathogenic Shiga toxin-producing Escherichia coli (STEC), such as O8, O22, O111, O174, and O179 strains. Serological typing of the H8 antigen is limited to motile strains only and suffers from cross-reactivity between flagellar H8 and H40 antigens. In order to develop a method useful for typing of motile and nonmotile STEC O111 and other strains, we have analyzed the flagellar antigen (fliC) genes in representative E. coli H8 and H40 types. Two genotypes of the fliC gene encoding H8 (the fliC-H8 gene) were identified. Genotype fliC-H8a was found to be conserved in STEC O111, O174, and O179 strains; and type fliC-H8b was associated with STEC O8 and O22 strains. Sequence variations were also found in the genetically closely related fliC-H40 gene, although the latter was not found to be associated with STEC strains. A PCR was developed for the specific identification of the fliC-H8 and the fliC-H40 genes in motile and nonmotile E. coli strains. Digestion of PCR products with HhaI resulted in restriction fragment length polymorphisms (RFLPs) which were associated with genotypes fliC-H8a and -H8b as well as with genotypes fliC-H40a and -H40b. The fliC-specific PCR/RFLP typing method was suitable for the rapid typing of motile and nonmotile STEC O8, O22, O111, O174, and O179 strains from different sources whose fliC-H8 genotypes were found to be highly conserved. The fliC genotyping method is advantageous over serotyping and is useful for epidemiological investigations and studies of the evolution of STEC clones.
In Escherichia coli, the waaP (rfaP) gene product was recently shown to be responsible for phosphorylation of the first heptose residue of the lipopolysaccharide (LPS) inner core region. WaaP was also shown to be necessary for the formation of a stable outer membrane. These earlier studies were performed with an avirulent rough strain of E. coli (to facilitate the structural chemistry required to properly define waaP function); therefore, we undertook the creation of a waaP mutant of Salmonella enterica serovar Typhimurium to assess the contribution of WaaP and LPS core phosphorylation to the biology of an intracellular pathogen. The S. enterica waaP mutant described here is the first to be both genetically and structurally characterized, and its creation refutes an earlier claim that waaP mutations in S. enterica must be leaky to maintain viability. The mutant was shown to exhibit characteristics of the deep-rough phenotype, despite its ability to produce a full-length core capped with O antigen. Further, phosphoryl modifications in the LPS core region were shown to be required for resistance to polycationic antimicrobials. The waaP mutant was significantly more sensitive to polymyxin in both wild-type and polymyxin-resistant backgrounds, despite the decreased negative charge of the mutant LPSs. In addition, the waaP mutation was shown to cause a complete loss of virulence in mouse infection models. Taken together, these data indicate that WaaP is a potential target for the development of novel therapeutic agents.
Among Escherichia coli strains of the O55:H7 serovar, which is considered the ancestor of Shiga toxin-producing E. coli (STEC) O157:H7, two subtypes, H7a,7b and H7a,7c (briefly, H7a,b and H7a,c, respectively), of the H7 flagellar antigen have been described previously [J. Wright and R. Villanueva, J. Hyg. (Camb.) 51:39-48, 1953; Y. A. Ratiner and V. A. Sinelnikova, Zh. Microbiol. Epidemiol. Immunobiol. 3:111-116, 1969). We have now studied 13 STEC O157:H7 strains and 1 O55:H7 strain that were epidemiologically unrelated, that originated from six countries on two continents, and that had different profiles when analyzed by multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and PCR for stx and eae. They were all found to possess the H7a,c flagellar antigen. Serum cross-absorption assays confirmed that their H antigens were indistinguishable from each other and from that of E. coli O55:H7a,c but differed from the standard H7a,b antigen of E. coli H test strain U5/41. It was shown by phage-mediated transduction that the flagellin genes for these two H-antigen subserotypes were alleles of the E. coli fliC locus. On the basis of the serological data obtained in this study and the molecular characteristics of E. coli fliCH7 alleles recently published, it is inferred that H7a,c and H7a,b are the main serological subtypes of the group of E. coli H7 flagellins.
Bolaños, Roger (Tulane University, New Orleans, La.), and Charles W. DeWitt. Isolation and characterization of the K1 (L) antigen of Escherichia coli. J. Bacteriol. 91:987–996. 1966.—An acidic polysaccharide with the serological properties of the K1 (L) antigen has been isolated from Escherichia coli O2:K1:H4 by means of phenol-water extraction, fractionation with hexadecyltrimethylammonium bromide (Cetavlon), filtration through Sephadex G-200, and chromatography on anion-exchange cellulose columns. Nucleic acid and protein content were reduced to a nondetectable level. There is no contamination with O antigen. The active material appears in two different positions in the Cetavlon fractionation, each with a slightly different serological specificity, as followed by the inhibition of passive hemagglutination. By paper chromatography, the polysaccharide moiety of the O antigenic fraction is composed of glucose, galactose, hexosamine and rhamnose. The absence of colanic acid in either K1 fraction was not proven, although its participation in our assay system, as well as the participation of the common or cross-reacting antigen, was ruled out by serological means.
The Escherichia coli blood culture isolate BK658 (O75:K1:H7) expresses F1A and F1B fimbriae as well as a third fimbrial type which reacts with anti-S-fimbrial antiserum but fails to show S-specific binding properties (i.e., agglutination of bovine erythrocytes). To characterize these fimbriae, we cloned the respective genetic determinant in E. coli K-12. The resulting recombinant clone HB101(pMMP658-6) expresses fimbriae of 1.2-micron length and a diameter of approximately 7 nm. The determinant codes for the fimbrillin subunit, a protein of 17 kilodaltons in size, and for at least five other proteins of 87, 31, 23, 14.3, and 13.8 kilodaltons. By restriction analysis and by DNA-DNA hybridization, it could be shown that the cloned fimbrial determinant of strain BK658 exhibits a high degree of sequence homology to the gene clusters coding for S fimbrial adhesins (sfa) and F1C fimbriae (foc). By using the Western blot (immunoblot) technique and a quantitative enzyme-linked immunosorbent assay, it could be further demonstrated that the cloned fimbriae of BK658, S fimbriae, and F1C fimbriae share cross-reactive epitopes as well as antigenic determinants specific for each fimbrial type. No antigenic cross-reactivity with F1C fimbriae could be detected. The results indicate a genetical and serological relatedness of the cloned fimbriae to S fimbriae and F1C fimbriae. Therefore, this new type of fimbriae is preliminarily termed S/F1C-related fimbriae (Sfr).
The etiological agent most commonly associated with bacillary dysentery is Shigella. As part of its mandate, the Bacteriology and Enteric Disease Program of Health Canada identifies and serotypes unusual isolates of Shigella received from provincial laboratories of public health. In this report, six unusual isolates from three provinces were analyzed biochemically and serologically using slide and tube agglutinations and molecularly using standard pulsed-filed gel electrophoresis (PFGE), PCR, and PCR-restriction fragment length polymorphism (RFLP) techniques. All six isolates were identical. PFGE analysis grouped these strains; biochemically, they were mannitol negative and consistent with the profile of Shigella. Serologically, these strains produced weak reactions in Shigella dysenteriae serovars 4 and 16 and Escherichia coli O159 and O173 antisera. Molecular serotyping by PCR-RFLP of the rfb gene produced an S. dysenteriae serovar 2/E. coli O112ac pattern. They were positive by PCR for ipaH and ial enteroinvasive genes but negative for all other genes tested. Antiserum was prepared from one of the isolates and tested against Shigella and E. coli reference strains as well as the other isolates. The antiserum reacted with the five remaining isolates and showed cross-reactivity with S. dysenteriae serovars 1, 4, and 16; Shigella flexneri type 3; and E. coli O118, O159, O168, O172, and O173 antigens. Absorbing the sera with E. coli O159 and S. dysenteriae serovar 4 antigen removed all cross-reactions and only slightly reduced the homologous titer. Based on biochemical, molecular, and complete serological analysis, we propose that these six isolates represent a new provisional serovar of S. dysenteriae, type strain BEDP 02-5104.
Wild canids and domestic dogs are the main reservoir of zoonotic visceral leishmaniasis (VL) caused by Leishmania infantum (syn.: Leishmania chagasi). Serological diagnosis of VL is therefore important in both human and dog leishmaniasis from a clinical and epidemiological point of view. Routine diagnosis of VL is traditionally carried out by immunofluorescent antibody test (IFAT), which is laborious and difficult to standardize and to interpret. In the last decade, however, several specific antigens of Leishmania infantum have been characterized, allowing the development of a recombinant-based immunoassay. Among them, the whole open reading frame encoding K9 antigen, the gene fragment encoding the repetitive sequence of K26, and the 3′-terminal gene fragment of the kinesin-related protein (K39sub) were previously evaluated as diagnostic markers for canine leishmaniasis and proved to be independent in their antibody reactivity. Since sensitivity of serological test is usually higher in multiple-epitope format, in this study the relevant epitopes of K9, K26, and K39 antigens were joined by PCR strategy to produce the chimeric recombinant protein. The resulting mosaic antigen was found highly expressed in Escherichia coli and efficiently purified by affinity chromatography. Antigenic properties of this recombinant antigen were evaluated by indirect enzyme-linked immunosorbent assay (ELISA) using a panel of human and dog sera previously characterized by parasitological and/or serological techniques. Chimeric ELISA showed 99% specificity in both human (n = 180) and canine (n = 343) control groups, while sensitivity was higher in canine VL (96%, n = 213) than in human VL (82%, n = 185). Accordingly, concordance between IFAT and canine chimeric ELISA (k = 0.95, 95% confidence interval = 0.93 to 0.98) was higher than between IFAT and human chimeric ELISA (k = 0.81, 95% confidence interval = 0.76 to 0.87). Results suggest the potential use of this new antigen for routine serodiagnosis of VL in both human and canine hosts.
Eight cases of hemolytic-uremic syndrome in which no pathogens were isolated were diagnosed serologically by a passive hemagglutination assay and a verotoxin (VT; Shiga-like toxin) enzyme-linked immunosorbent assay (ELISA). The passive hemagglutination assay employed formalinized sheep erythrocytes sensitized with soluble native antigen or heat-treated antigen (lipopolysaccharide [LPS]) from Escherichia coli O26, O111, O128, and O157 or flagellar antigen of nine different H serogroups of E. coli: H2, H7, H8, H10, H11, H12, H18, H19, and H25. All patients had antibodies against the native antigen and/or the LPS of E. coli O157, but positive agglutination with H7 was observed only in one patient. In the VT-ELISA with plates coated with purified VT 1 or VT 2, antibody against VT 2 was observed in the sera of five of six patients examined, but none of the patients possessed VT 1 antibody. These results indicate that the causative pathogen in these eight hemolytic-uremic syndrome cases is likely to be VT-producing E. coli O157. The passive hemagglutination assay described here is a very sensitive, simple, and rapid method. This assay is highly recommended for the serological diagnosis of VT-producing E. coli infections, particularly in patients infected by serogroup O157 strains. Furthermore, the VT-ELISA is useful in studying the role of VT in hemolytic-uremic syndrome.
Agglutination reactions obtained with three commercial latex reagents for detecting Escherichia coli O157 antigen (Oxoid Diagnostic Reagents, Hampshire, England; Pro-Lab Inc., Richmond Hill, Ontario, Canada; and Remel Microbiology Products, Lenexa, Kans.) and one for detecting H7 antigen (Remel) were compared with those obtained by standard serologic methods by using the Centers for Disease Control and Prevention (CDC) reference antisera for O157 and H7 antigens. For 159 strains of E. coli and related organisms, the Oxoid, Pro-Lab, and Remel O157 latex reagents each had a sensitivity and specificity of 100% compared with the CDC reference antiserum. For 106 strains of E. coli and related organisms that were not enhanced for motility through semisolid medium, the Remel H7 latex reagent had a sensitivity of 96% and a specificity of 100% compared with the standard tube agglutination method with CDC H7 antiserum. Measures to enhance motility were needed for some strains to detect the H7 antigen. Our findings demonstrate that the commercial latex reagents are good alternatives to standard serologic methods for identifying the O157 and H7 antigens of E. coli.
Escherichia coli is one of the best studied microorganisms and finds multiple applications especially as tool in the heterologous production of interesting proteins of other organisms. The heterologous expression of special surface (S-) layer proteins caused the formation of extremely long E. coli cells which leave transparent tubes when they divide into single E. coli cells. Such natural structures are of high value as bio-templates for the development of bio-inorganic composites for many applications. In this study we used genetically modified filamentous Escherichia coli cells as template for the design of polyelectrolyte tubes that can be used as carrier for functional molecules or particles. Diversity of structures of biogenic materials has the potential to be used to construct inorganic or polymeric superior hybrid materials that reflect the form of the bio-template. Such bio-inspired materials are of great interest in diverse scientific fields like Biology, Chemistry and Material Science and can find application for the construction of functional materials or the bio-inspired synthesis of inorganic nanoparticles.
Genetically modified filamentous E. coli cells were fixed in 2% glutaraldehyde and coated with alternating six layers of the polyanion polyelectrolyte poly(sodium-4styrenesulfonate) (PSS) and polycation polyelectrolyte poly(allylamine-hydrochloride) (PAH). Afterwards we dissolved the E. coli cells with 1.2% sodium hypochlorite, thus obtaining hollow polyelectrolyte tubes of 0.7 μm in diameter and 5–50 μm in length. For functionalisation the polyelectrolyte tubes were coated with S-layer protein polymers followed by metallisation with Pd(0) particles. These assemblies were analysed with light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy.
The thus constructed new material offers possibilities for diverse applications like novel catalysts or metal nanowires for electrical devices. The novelty of this work is the use of filamentous E. coli templates and the use of S-layer proteins in a new material construct.
Escherichia coli; S-layer; Polyelectrolytes; Layer-by-layer (LbL); Palladium; SEM; TEM; Nanoparticle
Tick-borne relapsing fever is caused by numerous Borrelia species maintained in nature by Ornithodoros tick-mammal cycles. Serological confirmation is based on either an immunofluorescence assay or an enzyme-linked immunosorbent assay using whole cells or sonicated Borrelia hermsii as the antigen. However, antigenic variability of this bacterium's outer surface proteins and antigens shared with the Lyme disease spirochete (B. burgdorferi), may cause both false-negative and false-positive results when testing sera of patients suspected to have either relapsing fever or Lyme disease. To develop a specific serological test for relapsing fever, we created a genomic DNA library of B. hermsii, screened transformed Escherichia coli cells for immunoreactivity with high-titered (> or = 1:2,048) human anti-B. hermsii antiserum, and selected an immunoreactive clone (pSPR75) expressing a 39-kDa protein. DNA sequencing, subcloning, and serum adsorption experiments identified the immunoreactive protein as a homolog of GlpQ, a glycerophosphodiester phosphodiesterase identified previously in E. coli, Haemophilus influenzae, and Bacillus subtilis. Serum samples from humans and mice infected with B. hermsii or other species of relapsing fever spirochetes contained antibodies recognizing GlpQ, whereas serum samples from Lyme disease and syphilis patients were nonreactive. Serologic tests based on this antigen will identify people exposed previously to relapsing fever spirochetes and help clarify the distribution of relapsing fever and Lyme disease in situations in which the occurrence of their causative agents is uncertain.
The genes controlling synthesis of Shigella flexneri group- and type-specific antigens were transferred to Escherichia coli K-12 recipients by conjugation with an S. flexneri Hfr. After mating E. coli with an Hfr strain of S. flexneri 2a and selecting for his+ recombinants, a high proportion of the E. coli hybrids agglutinated in S. flexneri grouping serum. None of these hybrids expressed S. flexneri type-specific antigen II. When an E. coli his+ hybrid possessing the S. flexneri group antigen was remated with the same Hfr with selection for pro+ hybrids, a high proportion now expressed the type-specific antigen as well as the previously inherited group antigen. If such crosses were performed in reverse order (i.e., pro+ followed by his+ selection), a different pattern of serological behavior was observed. None of the pro+ hybrids showed the type-specific antigen. Subsequent mating for his+ resulted in hybrids with both the group- and type-specific antigens. These results show that genes controlling the synthesis of S. flexneri group antigen (linked to the his locus) and type-specific antigen (linked to the pro locus) are widely separated on the chromosome. Expression of the type-specific antigen II depends on the presence of the group antigen.
Previously a Brucella protein named CP28, BP26, or Omp28 has been identified as an immunodominant antigen in infected cattle, sheep, goats, and humans. In the present study we evaluated antibody responses of infected and B. melitensis Rev.1-vaccinated sheep to the BP26 protein using purified recombinant BP26 protein produced in Escherichia coli in an indirect enzyme-linked immunosorbent assay (I-ELISA). The specificity of the I-ELISA determined with sera from healthy sheep (n = 106) was 93%. The sensitivity of the I-ELISA assessed with sera from naturally infected and suspected sheep found positive in the current conventional diagnostic tests was as follows: 100% for bacteriologically and serologically positive sheep (n = 50), 88% for bacteriologically negative but serologically and delayed-type hypersensitivity-positive sheep (n = 50), and 84% for bacteriologically and serologically negative but delayed-type hypersensitivity-positive sheep (n = 19). However, the absorbance values observed did not reach those observed in an I-ELISA using purified O-polysaccharide (O-PS) as an antigen. In sheep experimentally infected with B. melitensis H38 the antibody response to BP26 was delayed and much weaker than that to O-PS. Nevertheless, the BP26 protein appears to be a good diagnostic antigen to be used in confirmatory tests and for serological differentiation between infected and B. melitensis Rev.1-vaccinated sheep. Weak antibody responses to BP26 in some of the latter sheep suggest that a B. melitensis Rev.1 bp26 gene deletion mutant should be constructed to ensure this differentiation.
An enzyme-linked immunosorbent assay (ELISA) using two recombinant antigens of Toxoplasma gondii (GRA1 and GRA6 Nt) was developed in order to differentiate between pregnant women with a serological profile of recently acquired infection and those with chronic infection. Both proteins were expressed in Escherichia coli as glutathione S-transferase fusion proteins. Thirty-two serum samples from subjects who presented seroconversion within 3 months before sampling (group 1; acute profile), 46 serum samples from women who had a positive serology at least 1 year before sampling (group 2; chronic profile), and 100 serum samples from pregnant women who were not infected by T. gondii (group 3) were examined for immunoglobulin G (IgG) reactivity. For both antigens, the specificity reached 98%. In both groups of infected patients, the overall sensitivity scored was 60% for GRA1 and 83% for GRA6 Nt. In group 1, 34% of sera reacted with GRA1 whereas 84% of sera reacted with GRA6 Nt; in group 2, however, sensitivities were 78.2 and 82.6%, respectively. Combination of the readings obtained with both antigens yielded a sensitivity of 91%. A serological follow-up of 10 women who seroconverted during pregnancy displayed three different serological patterns: (i) a GRA profile paralleling the IgG curve, as detected by the commercial kit, (ii) a GRA1 profile, or (iii) GRA1 and GRA6 Nt profiles remaining negative for at least 8 weeks after the reference test gave positive results. Taken together, these results suggest that neither GRA1 nor GRA6 Nt is sensitive enough to be used routinely to differentiate between acute and chronic toxoplasmic infections.
One of the major challenges in contemporary synthetic biology is to find a route to engineer synthetic organisms with altered chemical constitution. In terms of core reaction types, nature uses an astonishingly limited repertoire of chemistries when compared with the exceptionally rich and diverse methods of organic chemistry. In this context, the most promising route to change and expand the fundamental chemistry of life is the inclusion of amino acid building blocks beyond the canonical 20 (i.e. expanding the genetic code). This strategy would allow the transfer of numerous chemical functionalities and reactions from the synthetic laboratory into the cellular environment. Due to limitations in terms of both efficiency and practical applicability, state-of-the-art nonsense suppression- or frameshift suppression-based methods are less suitable for such engineering. Consequently, we set out to achieve this goal by sense codon emancipation, that is, liberation from its natural decoding function – a prerequisite for the reassignment of degenerate sense codons to a new 21st amino acid. We have achieved this by redesigning of several features of the post-transcriptional modification machinery which are directly involved in the decoding process. In particular, we report first steps towards the reassignment of 5797 AUA isoleucine codons in Escherichia coli using efficient tools for tRNA nucleotide modification pathway engineering.
genetic code; sense codons; reassignment; orthogonal pairs; synthetic biology; codon emancipation
The O157:H7 clone of Escherichia coli, which causes major, often prolonged outbreaks of gastroenteritis with hemolytic-uremic syndrome (HUS) such as those in Japan, Scotland, and the United States recently, is thought to be resident normally in cattle or other domestic animals. This clone is of major significance for public health and the food industry. We have developed a fast method for sequencing a given O antigen gene cluster and applied it to O157. The O157 O antigen gene cluster is 14 kb in length, comprising 12 genes and a remnant H-repeat unit. Based on sequence similarity, we have identified all the necessary O antigen genes, including five sugar biosynthetic pathway genes, four transferase genes, the O unit flippase gene, and the O antigen polymerase gene. By PCR testing against all 166 E. coli O serogroups and a range of gram-negative bacterial strains, including some that cross-react serologically with E. coli O157 antisera, we have found that certain O antigen genes are highly specific to O157 E. coli. This work provides the basis for a sensitive test for rapid detection of O157 E. coli. This is important both for decisions on patient care, since early treatment may reduce the risk of life-threatening complications, and for detection of sources of contamination. The method for fast sequencing of O antigen gene clusters plus an ability to predict which genes will be O antigen specific will enable PCR tests to be developed as needed for other clones of E. coli or, once flanking genes are identified, clones of any gram-negative bacterium.