Immunological and genetical relatedness of type-1 and type-2 fimbriae in salmonellas of serotypes Gallinarum, Pullorum and Typhimurium

The fimbriae of 50 strains of serotype Gallinarum and 35 strains of serotype Pullorum of the genus Salmonella were compared with the type-1 fimbriae of serotype Typhimurium strains by immune electron microscopy and dot blot hybridization tests with gene probes for type-1 fimbriation in Typhimurium. The fimbriae of Gallinarum and Pullorum strains were coated with Typhimurium type-1 fimbrial anti-serum and probes hybridized strongly with DNA of Gallinarum and Pullorum strains under stringent conditions. Furthermore, when Typhimurium type-1 fimbrial antiserum, that had been absorbed with fimbriate Gallinarum or Pullorum bacteria, was used in immune gold labelling experiments, it was shown that residual antibody recognized sites of possible adhesin incorporation at intervals along the length of Typhimurium type-1 fimbriae. These findings suggest that the type-2 fimbriae produced by all Gallinarum and Pullorum strains are non-adhesive forms of adhesive, type-1 fimbriae. This observation is of interest because type-1 fimbriae have never been reported in naturally occurring strains of these two avian-adapted serotypes.     

Linkage of avian and reproductive tract tropism with sequence divergence adjacent to the 5S ribosomal subunit rrfH of Salmonella enterica

The 183 bp between the end of the 23S rrlH rRNA gene and the start of the 5S rrfH rRNA gene (ISR-1) and the 197 bp between the end of the rrfH rRNA gene and the start of the transfer RNA aspU (ISR-2) of Salmonella enterica ssp. enterica serotypes Enteritidis, Typhimurium, Pullorum, Heidelberg, Gallinarum, Typhi and Choleraesuis were compared. ISR-1s of D1 serotypes (Pullorum, Gallinarum and Enteritidis), B serotypes (Typhimurium and Heidelberg) and the C2 serotype Newport and the enteric fever pathogens serotype A Paratyphi and serotype D1 Typhi formed three clades, respectively. ISR-2 further differentiated the avian-adapted serotype Gallinarum from avian-adapted Pullorum and Salmonella bongori from S. enterica. The results suggest that serotypes Heidelberg and Choleraesuis share some evolutionary trends with egg-contaminating serotypes. In addition, ISR-1 and ISR-2 sequences that confirm serotype appear to be linked to clinically relevant host associations of the Salmonellae.     

Type V collagen as the target for type-3 fimbriae, enterobacterial adherence organelles

Tissue-binding specificity of the type-3 fimbriae of pathogenic enteric bacteria was determined using frozen sections of human kidney. A wild-type Klebsiella sp. strain and the recombinant strain Escherichia coli HB101(pFK12), both expressing type-3 fimbriae, as well as the purified type-3 fimbriae effectively bound to sites at or adjacent to tubular basement membranes, Bowman's capsule, arterial walls, and the interstitial connective tissue. Bacterial adherence to kidney was decreased after collagenase treatment of the tissue sections. Recombinant strains expressing type-3 fimbriae specifically adhered to type V collagen immobilized on glass slides, whereas other collagens, fibronectin or laminin did not support bacterial adherence. In accordance with these findings, specific binding of purified type-3 fimbriae to immobilized type V collagen was demonstrated. Specific adhesion to type V collagen was also seen with the recombinant strain HB101(pFK52/pDC17), which expresses the mrkD gene of the type-3 fimbrial gene cluster in association with the pap-encoded fimbrial filament of E. coli, showing that the observed binding was mediated by the minor lectin (MrkD) protein of the type-3 fimbrial filament. The interaction is highly dependent on the conformation of type V collagen molecules since type V collagen in solution did not react with the fimbriae. Specific binding to type V collagen was also exhibited by type-3 fimbriate strains of Yersinia and Salmonella, showing that the ability to use type V collagen as tissue target is widespread among enteric bacteria.     

Occurrence of type-1C fimbriae on Escherichia coli strains isolated from human extraintestinal infections

Two monoclonal antibodies specific for type-1C fimbriae of Escherichia coli were produced. In enzyme-linked immunosorbent assay and immunoblotting the antibodies, which were of the IgG1 isotype, reacted with type-1C, but not with P or type-1 fimbriae of E. coli strain KS71. Immunoblotting and immunoprecipitation of crude fimbrial extracts from 25 strains invariably gave an apparent molecular weight of 17 000 for the type-1C fimbrillin. A total of 313 E. coli strains, isolated from patients with extraintestinal infection or from faeces of healthy children, were screened for the presence of type-1C fimbriae using both the monoclonal and polyclonal antibodies. Of these, 45 (14%) strains had type-1C fimbriae, with the highest frequency (27%) on strains isolated from patients with pyelonephritis. No faecal strain had type-1C fimbriae, and the frequency on the other diagnostic groups ranged from 11 to 15%. Thus, no direct correlation between type-1C fimbriae and bacterial virulence in human extraintestinal infections was found. Type-1C fimbriae were detected on only a few E. coli serotypes, notably on all O6:K2:H1 and O22:K13:H1 strains tested.     

Kinetics of phase variation between S and type-1 fimbriae of Escherichia coli

Abstract The rate of fimbrial phase variation in Escherichia coli strain 3040 was determined. The strain has type-1 and S fimbriae. The bacterial culture was fractionated into homogeneous subpopulations expressing either one of the fimbrial types only; the subpopulations were inoculated into broth and the fimbriation of individual cells was assayed by immunofluorescence as a function of time. The rate of the shift from S- or type-1-fimbriate cells to non-fimbriate ones was of the order of 10⁻² per cell generation and more rapid than a direct shift from one fimbrial phase to another, although both types of phase variations were observed.     

Basement membrane carbohydrate as a target for bacterial adhesion: binding of type I fimbriae of Salmonella enterica and Escherichia coli to laminin

Adherence of type-1-fimbriate Salmonella enterica and Escherichia coli to immobilized proteins of the extracellular matrix and reconstituted basement membranes was studied. The type-1-fimbriate strain SH401 of S. enterica serovar Enteritidis showed good adherence to laminin, whereas the adherence to fibronectin, type I, type III, type IV or type V collagens was poor. Only minimal adherence to the matrix proteins was seen with a non-fimbriate strain of S. enterica serovar Typhimurium. A specific and mannoside-inhibitable adhesion to laminin was exhibited by the recombinant E. coli strain HB101(plSF101) possessing fim genes of Typhimurium. Adherence to laminin of strain SH401 was inhibited by Fab fragments against purified SH401 fimbriae, and a specific binding to laminin, of the purified fimbriae, was demonstrated using fimbriae-coated fluorescent microparticles. Periodate treatment of laminin abolished the bacterial adhesion as well as the fimbrial binding. Specific adhesion to immobilized laminin was also shown by the type-1 -fimbriate E. coli strain 2131 and the recombinant strain E. coli HB101(pPKL4) expressing the cloned type-1-fimbriae genes of E. coli. Adhesion to laminin of strain HB101(pPKL4) was inhibited by mannoside, and no adherence was seen with the fimH mutant E. coli HB101(pPKL5/pPKL53) lacking the fimbrial lectin subunit. The type-1 fimbriate strains also adhered to reconstituted basement membranes from mouse sarcoma cells and human placenta. Adhesion of strains HB101(plSF101) and HB101(pPKL4) to both basement membrane preparations was inhibited by mannoside. We conclude that type-1 fimbriae of S. enterica and E. coli bind to oMgomannoside chains of the lamjnjn network in basement membranes.     

Prevalence and Fimbrial Genotype Distribution of Poultry Salmonella Isolates in China (2006 to 2012)

In this study, a total of 323 Salmonella enterica strains were isolated from 3,566 rectal swab samples of 51 poultry farms in seven regions of 12 provinces of China between 2006 and 2012. The prevalences of Salmonella sp. carriage were 12.4% in geese (66 positive/533 samples), 10.4% in turkeys (32/309), 9.8% in chickens (167/1,706), 6.8% in ducks (41/601), and 4.1% in pigeons (17/417), respectively. These isolates belonged to 20 serovars, in which the most frequent serovars were S. enterica serovar Gallinarum biovar Pullorum (herein, S. Pullorum) (55 isolates, 17.0%), S. enterica serovar Typhimurium (50 isolates, 15.5%), and S. enterica serovar Enteritidis (39 isolates, 12.1%). Overall, S. Typhimurium was the most commonly detected serovar; among the individual species, S. Pullorum was most commonly isolated from chickens, S. Enteritidis was most common in ducks, S. Typhimurium was most common in geese and pigeons, and S. enterica serovar Saintpaul was most common in turkeys. PCR determination of 20 fimbrial genes demonstrated the presence of bcfD, csgA, fimA, stdB, and sthE genes and the absence of staA and stgA genes in these isolates, and other loci were variably distributed, with frequency values ranging from 11.8 to 99.1%. These 323 Salmonella isolates were subdivided into 41 different fimbrial genotypes, and of these isolate, 285 strains (88.2%) had 12 to 14 fimbrial genes. Our findings indicated that the Salmonella isolates from different poultry species were phenotypically and genetically diverse and that some fimbrial genes are more frequently associated with serovars or serogroups.     

Characterization of two genes encoding antigenically distinct type-1 fimbriae of Klebsiella pneumoniae

A uropathogenic isolate of Klebsiella pneumoniae was shown to exhibit a mannose-sensitive hemagglutinating phenotype and to produce type-1 fimbriae consisting of subunits with a different electrophoretic mobility than those previously investigated. The gene cluster encoding expression of fimbriae was cloned and the genetic organization of the encoded polypeptides was determined. The gene encoding the major fimbrial subunit was localized and further examined by nucleotide sequence analysis. Comparison of two K. pneumoniae fimbrial genes revealed a nucleotide sequence agreement of 73%, and amino acid sequence agreement of 84% for the mature fimbrial subunits. Predictions of putative antigenic sites were correlated with regions demonstrating amino acid variability. In agreement with these predictions, no serological cross-reactivity between both fimbrial proteins could be demonstrated using an enzyme-linked immunosorbent assay (ELISA).     

Binding specificity of Salmonella plasmid-encoded fimbriae assessed by glycomics

The Salmonella enterica serotype Typhimurium (S. Typhimurium) genome encodes 12 intestinal colonization factors of the chaperone/usher fimbrial assembly class; however, the binding specificity is known for only one of these adhesins, known as type 1 fimbriae. Here we explored the utility of glycomics to determine the carbohydrate binding specificity of plasmid-encoded fimbriae from S. Typhimurium. A cosmid carrying the pef operon was introduced into Escherichia coli and expression of fimbrial filaments composed of PefA confirmed by flow cytometry and immune-electron microscopy. Plasmid-encoded fimbriae were purified from the surface of E. coli, and the resulting preparation was shown to contain PefA as the sole major protein component. The binding of purified plasmid-encoded fimbriae to a glycanarray suggested that this adhesin specifically binds the trisaccharide Galbeta1-4(Fucalpha1-3)GlcNAc, also known as the Lewis X (Le(x)) blood group antigen. Results from the glycanarray were validated by enzyme-linked immunosorbent assay (ELISA) in which plasmid-encoded fimbriae bound Le(x)-coated wells in a concentration-dependent manner. The binding of plasmid-encoded fimbriae to Le(x)-coated wells could be inhibited by co-incubation with soluble Le(x) antigen. Our results establish glycomic analysis as a promising new approach for determining the carbohydrate binding specificity of bacterial adhesins.     

Identification of the genetic determinants of Salmonella enterica serotype Typhimurium that may regulate the expression of the type 1 fimbriae in response to solid agar and static broth culture conditions

Background

Type 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium. Previous investigations indicate that static broth culture favours S. Typhimurium to produce type 1 fimbriae, while non-fimbriate bacteria are obtained by growth on solid agar media. The phenotypic expression of type 1 fimbriae in S. Typhimurium is the result of the interaction and cooperation of several genes in the fim gene cluster. Other gene products that may also participate in the regulation of type 1 fimbrial expression remain uncharacterized.

Results

In the present study, transposon insertion mutagenesis was performed on S. Typhimurium to generate a library to screen for those mutants that would exhibit different type 1 fimbrial phenotypes than the parental strain. Eight-two mutants were obtained from 7,239 clones screened using the yeast agglutination test. Forty-four mutants produced type 1 fimbriae on both solid agar and static broth media, while none of the other 38 mutants formed type 1 fimbriae in either culture condition. The flanking sequences of the transposons from 54 mutants were cloned and sequenced. These mutants can be classified according to the functions or putative functions of the open reading frames disrupted by the transposon. Our current results indicate that the genetic determinants such as those involved in the fimbrial biogenesis and regulation, global regulators, transporter proteins, prophage-derived proteins, and enzymes of different functions, to name a few, may play a role in the regulation of type 1 fimbrial expression in response to solid agar and static broth culture conditions. A complementation test revealed that transforming a recombinant plasmid possessing the coding sequence of a NAD(P)H-flavin reductase gene ubiB restored an ubiB mutant to exhibit the type 1 fimbrial phenotype as its parental strain.

Conclusion

Genetic determinants other than the fim genes may involve in the regulation of type 1 fimbrial expression in S. Typhimurium. How each gene product may influence type 1 fimbrial expression is an interesting research topic which warrants further investigation.     

Genomic Comparison between Salmonella Gallinarum and Pullorum: Differential Pseudogene Formation under Common Host Restriction

Background

Salmonella serovars Enteritidis and Gallinarum are closely related, but their host ranges are very different: the former is host-promiscuous and the latter can infect poultry only. Comparison of their genomic sequences reveals that Gallinarum has undergone much more extensive degradation than Enteritidis. This phenomenon has also been observed in other host restricted Salmonella serovars, such as Typhi and Paratyphi A. The serovar Gallinarum can be further split into two biovars: Gallinarum and Pullorum, which take poultry as their common host but cause distinct diseases, with the former eliciting typhoid and the latter being a dysentery agent. Genomic comparison of the two pathogens, with a focus on pseudogenes, would provide insights into the evolutionary processes that might have facilitated the formation of host-restricted Salmonella pathogens.

Methodologies/Principal Findings

We sequenced the complete genome of Pullorum strains and made comparison with Gallinarum and other Salmonella lineages. The gene contents of Gallinarum and Pullorum were highly similar, but their pseudogene compositions differed considerably. About one fourth of pseudogenes had the same inactivation mutations in Gallinarum and Pullorum but these genes remained intact in Enteritidis, suggesting that the ancestral Gallinarum may have already been restricted to poultry. On the other hand, the remaining pseudogenes were either in the same genes but with different inactivation sites or unique to Gallinarum or Pullorum, reflecting unnecessary functions in infecting poultry.

Conclusions

Our results support the hypothesis that the divergence between Gallinarum and Pullorum was initiated and facilitated by host restriction. Formation of pseudogenes instead of gene deletion is the major form of genomic degradation. Given the short divergence history of Gallinarum and Pullorum, the effect of host restriction on genomic degradation is huge and rapid, and such effect seems to be continuing to work. The pseudogenes may reflect the unnecessary functions for Salmonella within the poultry host.     

A previously uncharacterized gene stm0551 plays a repressive role in the regulation of type 1 fimbriae in Salmonella enterica serotype Typhimurium

ABSTRACT: BACKGROUND: Salmonella enterica serotype Typhimurium produces surface-associated fimbriae that facilitate adherence of the bacteria to a variety of cells and tissues. Type 1 fimbriae with binding specificity to mannose residues are the most commonly found fimbrial type. In vitro, static-broth culture favors the growth of S. Typhimurium with type 1 fimbriae, whereas non-type 1 fimbriate bacteria are obtained by culture on solid-agar media. Previous studies demonstrated that the phenotypic expression of type 1 fimbriae is the result of the interaction and cooperation of the regulatory genes fimZ, fimY, fimW, and fimU within the fim gene cluster. Genome sequencing revealed a novel gene, stm0551, located between fimY and fimW that encodes an 11.4-kDa putative phosphodiesterase specific for the bacterial second messenger cyclic-diguanylate monophosphate (c-di-GMP). The role of stm0551 in the regulation of type 1 fimbriae in S. Typhimurium remains unclear. RESULTS: A stm0551-deleted stain constructed by allelic exchange constitutively produced type 1 fimbriae in both static-broth and solid-agar medium conditions. Quantative RT-PCR revealed that expression of the fimbrial major subunit gene, fimA, and one of the regulatory genes, fimZ, were comparably increased in the stm0551-deleted strain compared with those of the parental strain when grown on the solid-agar medium, a condition that normally inhibits expression of type 1 fimbriae. Following transformation with a plasmid possessing the coding sequence of stm0551, expression of fimA and fimZ decreased in the stm0551 mutant strain in both culture conditions, whereas transformation with the control vector pACYC184 relieved this repression. A purified STM0551 protein exhibited a phosphodiesterase activity in vitro while a point mutation in the putative EAL domain, substituting glutamic acid (E) with alanine (A), of STM0551 or a FimY protein abolished this activity. CONCLUSIONS: The finding that the stm0551 gene plays a negative regulatory role in the regulation of type 1 fimbriae in S. Typhimurium has not been reported previously. The possibility that degradation of c-di-GMP is a key step in the regulation of type 1 fimbriae warrants further investigation.     

CsgA is a pathogen-associated molecular pattern of Salmonella enterica serotype Typhimurium that is recognized by Toll-like receptor 2

Knowledge about the origin and identity of the microbial products recognized by the innate immune system is important for understanding the pathogenesis of inflammatory diseases. We investigated the potential role of Salmonella enterica serotype Typhimurium fimbriae as pathogen-associated molecular patterns (PAMPs) that may stimulate innate pathways of inflammation. We screened a panel of 11 mutants, each carrying a deletion of a different fimbrial operon, for their enteropathogenicity using the calf model of human gastroenteritis. One mutant (csgBA) was attenuated in its ability to elicit fluid accumulation and GROalpha mRNA expression in bovine ligated ileal loops. The mechanism by which thin curled fimbriae encoded by the csg genes contribute to inflammation was further investigated using tissue culture. The S. Typhimurium csgBA mutant induced significantly less IL-8 production than the wild type in human macrophage-like cells. Purified thin curled fimbriae induced IL-8 expression in human embryonic kidney (HEK293) cells transfected with Toll-like receptor (TLR) 2/CD14 but not in cells transfected with TLR5, TLR4/MD2/CD14 or TLR11. Fusion proteins between the major fimbrial subunit of thin curled fimbriae (CsgA) and glutathione-S-transferase (GST) elicited IL-8 production in HEK293 cells transfected with TLR2/CD14. Proteinase K treatment abrogated IL-8 production elicited in these cells by GST-CsgA, but not by synthetic lipoprotein. GST-CsgA elicited more IL-6 production than GST in bone marrow-derived macrophages from TLR2+/+ mice, while there was no difference in IL-6 secretion between GST-CsgA and GST in macrophages from TLR2-/- mice. These data suggested that CsgA is a PAMP that is recognized by TLR2.     

Characterization of a putative colonization factor (PCFO166) of enterotoxigenic Escherichia coli of serogroup O166

Enterotoxigenic Escherichia coli (ETEC) of serogroup O166 gave mannose-resistant haemagglutination (MRHA) with bovine and human erythrocytes. The strains did not react with antisera prepared against the known colonization factors CFA/I, CFA/II, CFA/III, CFA/IV and PCFO159:H4. Strain E7476 of serotype O166:H27, which produced heat-stable enterotoxin (ST), was examined initially. It produced fimbriae about 7 nm in diameter. On SDS-PAGE two possible fimbrial polypeptides of molecular mass 15.5 and 17.0 kDa were seen. When variants of strain E7476 were isolated, loss of ST and MRHA together was associated with loss of a 98 MDa plasmid, while loss of ST alone correlated with plasmid deletion. An absorbed anti-strain E7476 antiserum reacted specifically with the 15.5 and 17.0 kDa polypeptides in Western immunoblotting and bound to the intact fimbriae by immuno-electron microscopy. When this antiserum was used in an ELISA to examine other strains of serogroup O166, a positive reaction was obtained with all the ST- and MRHA-positive strains. One strain of serotype O71:H27 and two strains of serotype O98:H- also reacted with the absorbed anti-strain E7476 antiserum. The antiserum did not react with ETEC carrying known colonization factors. E. coli K12 and a number of E. coli of different serotypes carrying a plasmid coding for ST transferred from strain E7476, all gave MRHA and reacted with the absorbed anti-strain E7476 antiserum. The term putative colonization factor O166 (PCFO166) is proposed to describe the adhesive factor(s) on ETEC of serogroup O166 because of the similarity of properties with those of known colonization factors.     

Genomic heterogeneity in Chlorobium limicola: chromosomic and plasmidic differences among strains

Abstract The purpose of this study is to certify the importance of the fimbriae as an attachment factor of Actinobacillus actinomycetemcomitans , a human periodontopathic bacterium, and the significance of anti-fimbrial antibody function as an attachment inhibitor. Fimbrial antigen was prepared from the A. actinomycetemcomitans 310-a strain. Oligopeptides were synthesized according to the amino acid sequence of the fimbrial protein. The peptide antigen was conjugated with branched lysine polymer resin beads. The peptide antigen was suspended in PBS emulsified with incomplete Freund's adjuvant and used to immunize rabbits. A rabbit antiserum reacted with an approximately 54 kDa protein of the fimbriae protein from A. actinomycetemcomitans 310-a and with those of other fimbriated strains. This antiserum strongly inhibited the attachment of fimbriated A. actinomycetemcomitans strains to saliva-coated hydroxyapatite beads, buccal epithelial cells, and a fibroblast cell line, Gin-1. Such a synthetic fimbrial peptide antigen may be effective in inducing antibodies which inhibit adhesion and subsequent colonization by A. actinomycetemcomitans .     

Population heterogeneity of Salmonella enterica serotype Typhimurium resulting from phase variation of the lpf operon in vitro and in vivo

The lpf fimbrial operon oscillates between phase ON and phase OFF expression states, thereby generating heterogeneity within S. enterica serotype Typhimurium populations with regard to expression of long polar fimbrial antigens. To determine whether the proportion of lpf phase variants changes with growth conditions, the lpf phase ON content of cultures was determined after in vitro and in vivo passage. After passage in Luria-Bertani (LB) broth for 120 generations, 96% of cells in a serotype Typhimurium culture carried the lpf operon in the phase ON expression state, regardless of the phase ON/OFF ratio in the inoculum. In contrast, a culture passaged on LB agar plates for 500 generations contained approximately 2% lpf phase ON cells. Differences in the lpf phase ON content of cultures passaged in broth and on plates were not caused by an outgrowth of lpf phase ON or lpf phase OFF cells, since deletion of lpf biosynthesis genes did not alter the phase ON/OFF ratio attained after passage. Instead, growth in LB broth resulted in a eightfold increase in the phase OFF-to-ON transition frequency and a decrease of the lpf phase ON-to-OFF transition frequency by a factor of 150 compared to growth on LB agar plates. After infection of na?ve CBA/J mice with an lpf phase ON culture of serotype Typhimurium, the proportion of lpf phase ON cells continuously decreased over time, regardless of whether the strain carried intact fimbrial biosynthesis genes. These data suggest that elaboration of fimbriae does not have a major influence on the population heterogeneity produced by phase variation of the lpf operon in na?ve mice.     

Immunofluorescence study of fimbrial phase variation in Escherichia coli KS71

An immunofluorescence assay was developed to study fimbrial phase variation in a pyelonephritogenic Escherichia coli strain, KS71. By using fluorochrome-labeled antibodies specific for either P, type-1C, or type-1 fimbriae of strain KS71, it was shown that in a broth culture of strain KS71 the fimbrial types mostly occurred on different cells. Only 9% of the cells carried more than one fimbrial type. The KS71 cell population was fractionated into subpopulations expressing only one of the fimbrial types or lacking fimbriae. Immunofluorescence assay of the subpopulations revealed a rapid phase variation in fimbrial synthesis. Kinetic analyses of a nonfimbriated cell population suggested that a change from one fimbrial phase to another was not totally random.     

RosE represses Std fimbrial expression in Salmonella enterica serotype Typhimurium

The Salmonella enterica serotype Typhimurium ( S. typhimurium ) genome contains a large repertoire of putative fimbrial operons that remain poorly characterized because they are not expressed in vitro . In this study, insertions that induced expression of the putative stdABCD fimbrial operon were identified from a random bank of transposon mutants by screening with immuno-magnetic particles for ligand expression (SIMPLE). Transposon insertions upstream of csgC and lrhA or within dam , setB and STM4463 (renamed rosE ) resulted in expression of StdA and its assembly into fimbrial filaments on the cell surface. RosE is a novel negative regulator of Std fimbrial expression as indicated by its repression of a std :: lacZ reporter construct and by binding of the purified protein to a DNA region upstream of the stdA start codon. Expression of Std fimbriae in the rosE mutant resulted in increased attachment of S. typhimurium to human colonic epithelial cell lines (T-84 and CaCo-2). A rosE mutant exhibited a reduced ability to compete with virulent S. typhimurium for colonization of murine organs, while no defect was observed when both competing strains carried a stdAB deletion. These data suggest that a tight control of Std fimbrial expression mediated by RosE is required during host pathogen interaction.     

Purification and Characterization of Type 1 Fimbriae of Salmonella typhi

Type 1 fimbriae have been purified from a Salmonella typhi strain of clinical origin. Purified fimbriae retained their ability to bind to erythrocytes in a mannose-inhibitable fashion and, in doing so, behaved preferentially as a monovalent adhesin. SDS-PAGE analysis of the fimbrial preparation showed the presence of a 20-kDa major polypeptide component (fimbrillin) and of additional larger polypeptides present in smaller amounts. The amino-terminal sequence of fimbrillin was determined and turned out to be very similar but not identical to that of type 1 fimbrillins of other Salmonella serovars. A Western blot analysis of the purified fimbrial preparation using an antiserum raised against native fimbriae suggested that fimbrial proteins did not carry any major sequential epitope and that, in native fimbriae, conformational epitopes, possibly generated between different subunits, might provide for the major immunogenic epitopes. Analysis of different S. typhi clinical isolates using the anti-fimbrial antiserum showed an overall immunological similarity of these structures within this serovar.     

Immunogenicity of Vibrio cholerae O1 Fimbriae in Animal and Human Cholera

Parenteral immunization with either formalin-fixed whole cells of the fimbriate Bgd17 strain or purified fimbriae protected against Vibrio cholerae O1 infection in rabbits, independent of biotype and serotype. Parenteral immunization of adult rabbits with purified fimbriae prior to V. cholerae O1 challenge resulted in a reduction of 2 to 3 orders of magnitude in the number of bacteria recovered from the small intestines of immunized rabbits in comparison to non-immunized controls. IgG and IgA antibodies against fimbrillin of V. cholerae O1 were detected in the convalescent sera of patients with cholera; however, little fimbrial antigen was detected in the commercially available cholera vaccines when examined by polyclonal and monoclonal antibodies against fimbriae. These data suggest that fimbrial hemagglutinin is a major adhesin of V. cholerae O1 and that parenteral immunization with fimbriae generates a specific immune response in the gut that may serve as one means of mitigating subsequent V. cholerae O1 gut infection.