Antimicrobial susceptibility, serotype distribution, virulence profile and molecular typing of piliated clinical isolates of pneumococci from east coast, Peninsular Malaysia

Pilus has been recently associated with pneumococcal pathogenesis in humans. The information regarding piliated isolates in Malaysia is scarce, especially in the less developed states on the east coast of Peninsular Malaysia. Therefore, we studied the characteristics of pneumococci, including the piliated isolates, in relation to antimicrobial susceptibility, serotypes, and genotypes at a major tertiary hospital on the east coast of Peninsular Malaysia. A total of 100 clinical isolates collected between September 2017 and December 2019 were subjected to serotyping, antimicrobial susceptibility test, and detection of pneumococcal virulence and pilus genes. Multilocus sequence typing (MLST) and phylogenetic analysis were performed only for piliated strains. The most frequent serotypes were 14 (17%), 6A/B (16%), 23F (12%), 19A (11%), and 19F (11%). The majority of isolates were resistant to erythromycin (42%), tetracycline (37%), and trimethoprim-sulfamethoxazole (24%). Piliated isolates occurred in a proportion of 19%; 47.3% of them were multidrug-resistant (MDR) and a majority had serotype 19F. This study showed ST236 was the most predominant sequence type (ST) among piliated isolates, which was related to PMEN clone Taiwan19F-14 (CC271). In the phylogenetic analysis, the piliated isolates were grouped into three major clades supported with 100% bootstrap values. Most piliated isolates belonged to internationally disseminated clones of S. pneumoniae, but pneumococcal conjugate vaccines (PCVs) have the potential to control them.

Species-Specific Recognition of Sulfolobales Mediated by UV-Inducible Pili and S-Layer Glycosylation Patterns

The UV-inducible pili system of Sulfolobales (Ups) mediates the formation of species-specific cellular aggregates. Within these aggregates, cells exchange DNA to repair DNA double-strand breaks via homologous recombination. Substitution of the Sulfolobus acidocaldarius pilin subunits UpsA and UpsB with their homologs from Sulfolobus tokodaii showed that these subunits facilitate species-specific aggregation. A region of low conservation within the UpsA homologs is primarily important for this specificity. Aggregation assays in the presence of different sugars showed the importance of N-glycosylation in the recognition process. In addition, the N-glycan decorating the S-layer of S. tokodaii is different from the one of S. acidocaldarius Therefore, each Sulfolobus species seems to have developed a unique UpsA binding pocket and unique N-glycan composition to ensure aggregation and, consequently, also DNA exchange with cells from only the same species, which is essential for DNA repair by homologous recombination.IMPORTANCE Type IV pili can be found on the cell surface of many archaea and bacteria where they play important roles in different processes. The UV-inducible pili system of Sulfolobales (Ups) pili from the crenarchaeal Sulfolobales species are essential in establishing species-specific mating partners, thereby assisting in genome stability. With this work, we show that different Sulfolobus species have specific regions in their Ups pili subunits, which allow them to interact only with cells from the same species. Additionally, different Sulfolobus species have unique surface-layer N-glycosylation patterns. We propose that the unique features of each species allow the recognition of specific mating partners. This knowledge for the first time gives insights into the molecular basis of archaeal self-recognition.

Application of MLST and pilus gene sequence comparisons to investigate the population structures of Actinomyces naeslundii and Actinomyces oris

Actinomyces naeslundii and Actinomyces oris are members of the oral biofilm. Their identification using 16S rRNA sequencing is problematic and better achieved by comparison of metG partial sequences. A. oris is more abundant and more frequently isolated than A. naeslundii. We used a multi-locus sequence typing approach to investigate the genotypic diversity of these species and assigned A. naeslundii (n = 37) and A. oris (n = 68) isolates to 32 and 68 sequence types (ST), respectively. Neighbor-joining and ClonalFrame dendrograms derived from the concatenated partial sequences of 7 house-keeping genes identified at least 4 significant subclusters within A. oris and 3 within A. naeslundii. The strain collection we had investigated was an under-representation of the total population since at least 3 STs composed of single strains may represent discrete clusters of strains not well represented in the collection. The integrity of these sub-clusters was supported by the sequence analysis of fimP and fimA, genes coding for the type 1 and 2 fimbriae, respectively. An A. naeslundii subcluster was identified with both fimA and fimP genes and these strains were able to bind to MUC7 and statherin while all other A. naeslundii strains possessed only fimA and did not bind to statherin. An A. oris subcluster harboured a fimA gene similar to that of Actinomyces odontolyticus but no detectable fimP failed to bind significantly to either MUC7 or statherin. These data are evidence of extensive genotypic and phenotypic diversity within the species A. oris and A. naeslundii but the status of the subclusters identified here will require genome comparisons before their phylogenic position can be unequivocally established.

Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers

Uropathogenic Escherichia coli (UPEC) express various kinds of organelles, so-called pili or fimbriae, that mediate adhesion to host tissue in the urinary tract through specific receptor-adhesin interactions. The biomechanical properties of these pili have been considered important for the ability of bacteria to withstand shear forces from rinsing urine flows. Force-measuring optical tweezers have been used to characterize individual organelles of F1C type expressed by UPEC bacteria with respect to such properties. Qualitatively, the force-versus-elongation response was found to be similar to that of other types of helix-like pili expressed by UPEC, i.e., type 1, P, and S, with force-induced elongation in three regions, one of which represents the important uncoiling mechanism of the helix-like quaternary structure. Quantitatively, the steady-state uncoiling force was assessed as 26.4 ±1.4 pN, which is similar to those of other pili (which range from 21 pN for S(I) to 30 pN for type 1). The corner velocity for dynamic response (1,400 nm/s) was found to be larger than those of the other pili (400-700 nm/s for S and P pili, and 6 nm/s for type 1). The kinetics were found to be faster, with a thermal opening rate of 17 Hz, a few times higher than S and P pili, and three orders of magnitude higher than type 1. These data suggest that F1C pili are, like P and S pili, evolutionarily selected to primarily withstand the conditions expressed in the upper urinary tract.

Type-IV pili spectroscopic markers: applications in the quantification of piliation levels in Moraxella bovis cells by a FT-IR ANN-based model

Type-IV pili are cell surface organelles found in a wide variety of Gram-negative bacteria. They have traditionally been detected by electron microscopy and ELISA techniques. However, these methodologies are not appropriate for the rapid discrimination and quantification of piliated and nonpiliated cells in industrial or field conditions. Here, the analysis of FT-IR spectra of piliated, nonpiliated and sheared Moraxella bovis cells, together with purified pili suspensions spectra, allowed the identification of 3 IR regions associated to spectroscopic markers of Type-IV pili: 1750-1600, 1450-1350 and 1280-950 cm(-1). Such IR-specific markers were found for piliated cells grown in different culture systems (liquid or solid media), independently of the strain or pili serotype. They were also sensitive to pili expression levels. Therefore, on the bases of these specific spectral features, an FT-IR ANN-based model was developed to classify piliation levels in 5 distinct groups. An overall classification rate of almost 90% demonstrates the strong potential of the ANN system developed to monitor M. bovis cultures in vaccine production.

Specific involvement of pilus type 2a in biofilm formation in group B Streptococcus

Streptococcus agalactiae is the primary colonizer of the anogenital mucosa of up to 30% of healthy women and can infect newborns during delivery and cause severe sepsis and meningitis. Persistent colonization usually involves the formation of biofilm and increasing evidences indicate that in pathogenic streptococci biofilm formation is mediated by pili. Recently, we have characterized pili distribution and conservation in 289 GBS clinical isolates and we have shown that GBS has three pilus types, 1, 2a and 2b encoded by three corresponding pilus islands, and that each strain carries one or two islands. Here we have investigated the capacity of these strains to form biofilms. We have found that most of the biofilm-formers carry pilus 2a, and using insertion and deletion mutants we have confirmed that pilus type 2a, but not pilus types 1 and 2b, confers biofilm-forming phenotype. We also show that deletion of the major ancillary protein of type 2a did not impair biofilm formation while the inactivation of the other ancillary protein and of the backbone protein completely abolished this phenotype. Furthermore, antibodies raised against pilus components inhibited bacterial adherence to solid surfaces, offering new strategies to prevent GBS infection by targeting bacteria during their initial attachment to host epithelial cells.

Identification of Edwardsiella ictaluri and E. tarda by species-specific polymerase chain reaction targeted to the upstream region of the fimbrial gene

Phylogenetic analysis of nine strains of Edwardsiella ictaluri and eight strains of E. tarda (six typical motile strains and two atypical nonmotile strains) isolated from diseased fish was performed using the upstream region of the fimbrial gene cluster. Strains of E. ictaluri and E. tarda were significantly clustered into separate groups. Moreover, atypical E. tarda strains were clustered into a different group from the other strains. Three polymerase chain reaction (PCR) primer sets for differential detection of E. ictaluri as well as typical and atypical E. tarda were developed from the respective characteristic sequences. Strains of E. ictaluri, typical E. tarda, and atypical E. tarda were specifically detected by PCR using each primer set. No amplifications were observed after the use of these three primer sets with 25 other bacterial species, including fish pathogens. In addition, the three primer sets were able to detect the DNA of each target species from fish kidney and liver artificially infected with E. ictaluri or E. tarda.

Type III secretion system-associated pilus of Pseudomonas syringae as an epitope display tool

Type III secretion system-associated pili found in several plant pathogenic bacteria are required for injection of virulence proteins from bacteria into the plant cells. The possibility to use the type III secretion pilus of Pseudomonas syringae as an epitope display tool was studied. The advantage of the type III secretion pilus, compared with conventional fimbrial epitope display tools, is that the pilin subunits of the type III secretion pilus can auto-assemble into intact pili in vitro. Various peptides were inserted into the type III secretion pilin subunit, and secretion, assembly and surface properties of the modified pili were monitored. It was concluded that the outwards-projecting N-terminal region of the pilin can bear even 43 amino acids insertion. The three-dimensional structure of the epitope, however, can restrict the use of the pilus as an epitope display tool: a beta-hairpin structure was poorly tolerated.

Characterization of adhesin variants in Indian isolates of enteroaggregativeEscherichia coli

Enteroaggregative Escherichia coli (EAEC) are causative agents of diarrhea, being characterized by aggregative adherence to cultured epithelial cells. In this study, phenotypic properties of EAEC were analyzed with respect to AA, hemagglutination, clump and biofilm formation, all of which are mediated by aggregative adherence fimbriae (AAF). The strains were also screened for AAF types, AAF adhesin variants and Dr adhesin by PCR. Of the three known AAF types, AAF/I and AAF/II adhesin variants were identified. An association between the AAF/adhesin genotypes and the subtypes/scores of phenotypic properties was sought and it was observed that strains harboring same adhesins displayed different subtypes/scores and vice versa.

Aptamers that preferentially bind type IVB pili and inhibit human monocytic-cell invasion by Salmonella enterica serovar typhi

Salmonella enterica serovar Typhi is an important pathogen exclusively for humans and causes typhoid or enteric fever. It has been shown that type IVB pili, encoded by the S. enterica serovar Typhi pil operon located in Salmonella pathogenicity island 7, are important in the pathogenic process. In this study, by using both an adhesion-invasion assay and fluorescence quantitative PCR analysis, we demonstrated that the entry of type IVB piliated S. enterica serovar Typhi A21-6 (pil(+) Km(r)) into human THP-1 monocytic cells was greater than that of a nonpiliated S. enterica serovar Typhi pilS::Km(r) (pil mutant) strain. We have applied a systematic evolution of ligands by exponential enrichment approach to select oligonucleotides (aptamers) as ligands that specifically bind to type IVB pili. Using this approach, we identified a high-affinity single-stranded RNA aptamer (S-PS(8.4)) as a type IVB pilus-specific ligand and further found that the selected aptamer (S-PS(8.4)) could significantly inhibit the entry of the piliated strain (but not that of the nonpiliated strain) into human THP-1 cells. The binding affinities between aptamers and pre-PilS (structural protein of type IVB pili) were determined by nitrocellulose filter-binding assays, and the K(d) value was determined to be 8.56 nM for the S-PS(8.4) aptamer alone. As an example of an aptamer against type IVB pili of S. enterica serovar Typhi, the aptamer S-PS(8.4) can serve as a tool for analysis of bacterial type IVB pilus-host cell interactions and may yield information for the development of putative new drugs against S. enterica serovar Typhi bacterial infections, useful both in prevention of infection and in therapeutic treatment.

The Distinct Binding Specificities Exhibited by Enterobacterial Type 1 Fimbriae Are Determined by Their Fimbrial Shafts

Type 1 fimbriae of enterobacteria are heteropolymeric organelles of adhesion composed of FimH, a mannose-binding lectin, and a shaft composed primarily of FimA. We compared the binding activities of recombinant clones expressing type 1 fimbriae from Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium for gut and uroepithelial cells and for various soluble mannosylated proteins. Each fimbria was characterized by its capacity to bind particular epithelial cells and to aggregate mannoproteins. However, when each respective FimH subunit was cloned and expressed in the absence of its shaft as a fusion protein with MalE, each FimH bound a wide range of mannose-containing compounds. In addition, we found that expression of FimH on a heterologous fimbrial shaft, e.g. K. pneumoniae FimH on the E. coli fimbrial shaft or vice versa, altered the binding specificity of FimH such that it closely resembled that of the native heterologous type 1 fimbriae. Furthermore, attachment to and invasion of bladder epithelial cells, which were mediated much better by native E. coli type 1 fimbriae compared with native K. pneumoniae type 1 fimbriae, were found to be dependent on the background of the fimbrial shaft (E. coli versus K. pneumoniae) rather than the background of the FimH expressed. Thus, the distinct binding specificities of different enterobacterial type 1 fimbriae cannot be ascribed solely to the primary structure of their respective FimH subunits, but are also modulated by the fimbrial shaft on which each FimH subunit is presented, possibly through conformational constraints imposed on FimH by the fimbrial shaft. The capacity of type 1 fimbrial shafts to modulate the tissue tropism of different enterobacterial species represents a novel function for these highly organized structures.

Evolutionary and functional relationships of colonization factor antigen i and other class 5 adhesive fimbriae of enterotoxigenic Escherichia coli

Colonization factor antigen I (CFA/I) is the archetype of eight genetically related fimbriae of enterotoxigenic Escherichia coli (ETEC) designated class 5 fimbriae. Assembled by the alternate chaperone pathway, these organelles comprise a rigid stalk of polymerized major subunits and an apparently tip-localized minor adhesive subunit. We examined the evolutionary relationships of class 5-specific structural proteins and correlated these with functional properties. We sequenced the gene clusters encoding coli surface antigen 4 (CS4), CS14, CS17, CS19, and putative colonization factor antigen O71 (PCFO71) and analyzed the deduced proteins and the published homologs of CFA/I, CS1, and CS2. Multiple alignment and phylogenetic analysis of the proteins encoded by each operon define three subclasses, 5a (CFA/I, CS4, and CS14), 5b (CS1, CS17, CS19, and PCFO71), and 5c (CS2). These share distant evolutionary relatedness to fimbrial systems of three other genera. Subclass divisions generally correlate with distinguishing in vitro adherence phenotypes of strains bearing the ETEC fimbriae. Phylogenetic comparisons of the individual structural proteins demonstrated greater intrasubclass conservation among the minor subunits than the major subunits. To correlate this with functional attributes, we made antibodies against CFA/I and CS17 whole fimbriae and maltose-binding protein fusions with the amino-terminal half of the corresponding minor subunits. Anti-minor subunit Fab preparations showed hemagglutination inhibition (HAI) of ETEC expressing homologous and intrasubclass heterologous colonization factors while anti-fimbrial Fab fractions showed HAI activity limited to colonization factor-homologous ETEC. These results were corroborated with similar results from the Caco-2 cell adherence assay. Our findings suggest that the minor subunits of class 5 fimbriae may be superior to whole fimbriae in inducing antiadhesive immunity.

Variations of Porphyromonas gingivalis fimbriae in relation to microbial pathogenesis

OBJECTIVES

Periodontal disease is an infectious disorder caused by a small subset of periodontal pathogens including Porphyromonas gingivalis. Accumulated evidences show that the expression of P. gingivalis heterogenic virulence properties is dependent on its clonal diversity. P. gingivalis expresses two distinct fimbria molecules, major and minor fimbriae, on its cell surfaces, both of which seem to be involved in the development of periodontitis. In this short review, variations of fimbriae in relation to microbial pathogenesis are discussed.

MATERIALS AND METHODS

Our recent findings are summarized to elucidate the relationship between clonal variation of fimbriae and bacterial pathogenicity of various strains.

RESULTS

Major fimbriae were classified into six types (I to V and Ib) based on the diversity of fimA genes encoding FimA (a subunit of major fimbriae). A majority of periodontitis patients were found to carry type II fimA organisms, followed by type IV, and type II fimA organisms were significantly occurred with more severe forms of periodontitis. Studies of clones with type II fimA have revealed significantly greater adhesive and invasive capabilities to epithelial cells than other fimA type clones. Minor fimbriae induced interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) cytokine expression in macrophages and were suggested to be a causative factor of alveolar bone resorption in animal models. The clonal diversity of minor fimbriae is unclear, however, distinct minor fimbria molecules were found in different strains.

CONCLUSION

The fimbria variations may have an influence on the development of periodontal disease.

The type IVB pili of Salmonella enterica serovar Typhi bind to the cystic fibrosis transmembrane conductance regulator

Salmonella enterica serovar Typhi expresses type IVB pili. We show that the prePilS protein (the soluble precursor form of the structural pilin) interacts with a 15-mer peptide representing the first extracellular domain of the cystic fibrosis transmembrane conductance regulator (CFTR), a recognized human epithelial cell receptor for serovar Typhi (G. B. Pier et al., Nature 393:79-82, 1998). This indicates that after mediating bacterial self-association (C. Morris et al., Infect. Immun. 71:1141-1146, 2003), the pili then act to attach the bacterial clumps to CFTR in the membrane of gut epithelial cells. These sequential type IVB pilus-mediated events cannot be performed by (for example) S. enterica serovar Typhimurium, which may explain why only serovar Typhi causes epidemics of enteric fever in humans.

Exploring the 3D molecular architecture of Escherichia coli type 1 pili

An integrated approach combining information gained by Fourier transformation, linear Markham superposition (real space) and mass-per-length measurement by scanning transmission electron microscopy was used to analyze the helical structure of the rod-like type 1 pili expressed by uropathogenic Escherichia coli strain W3110. The 3D reconstruction calculated from the experimental data showed the pili to be 6.9nm wide, right-handed helical tubes with a 19.31(+/-0.34)nm long helical repeat comprising 27 FimA monomers associated head-to-tail in eight turns of the genetic one-start helix. Adjacent turns of the genetic helix are connected via three binding sites making the pilus rod rather stiff. In situ immuno-electron microscopy experiments showed the minor subunit (FimH) mediating pilus adhesion to bladder epithelial cells to be the distal protein of the pilus tip, which had a spring-like appearance at higher magnification. The subunits FimG and FimF connect FimH to the FimA rod, the sequential orientation being FimA-FimF-FimG-FimH. The electron density map calculated at 18A resolution from an atomic model of the pilus rod (built using the pilin domain FimH together with the G1 strand of FimC as a template for FimA and applying the optimal helical parameters determined to the head-to-tail interaction model for pilus assembly) was practically identical with that of the actual 3D reconstruction.

Cytokine production induced by a 67-kDa fimbrial protein from Porphyromonas gingivalis

Fimbriae have been reported to play an important role in the adherence of Porphyromonas gingivalis to oral surfaces and possibly in triggering host responses. P. gingivalis ATCC 33277 has two distinctly different fimbriae expressed on the cell surface. The 67-kDa fimbriae differ in size and antigenicity from the earlier reported FimA, a major 41-kDa fimbrial component of P. gingivalis. Expression of the 67-kDa fimbriae on the cell surface of a fimA mutant was investigated by electron microscopy. The 67-kDa fimbrial protein was purified from the fimA mutant by sonication, precipitation, and chromatography on a DEAE Sepharose CL-6B column. The N-terminal amino acid sequence of the 67-kDa fimbrillin was distinct from that of the 41-kDa fimbrillin. Moreover, we have found that the 67-kDa fimbrial protein from P. gingivalis ATCC 33277 induced IL-1alpha, IL-beta, IL-6 and TNFalpha cytokine expression in mouse peritoneal macrophages. These results suggest that P. gingivalis 67-kDa fimbriae may play a part in the inflammatory response during the development of periodontal diseases.

Different type 1 fimbrial genes and tropisms of commensal and potentially pathogenic Actinomyces spp. with different salivary acidic proline-rich protein and statherin ligand specificities

Actinomyces spp. exhibit type 1 fimbria-mediated adhesion to salivary acidic proline-rich proteins (PRPs) and statherin ligands. Actinomyces spp. with different animal and tissue origins belong to three major adhesion types as relates to ligand specificity and type 1 fimbria genes. (i) In preferential acidic-PRP binding, strains of Actinomyces naeslundii genospecies 1 and 2 from human and monkey mouths displayed at least three ligand specificities characterized by preferential acidic-PRP binding. Slot blot DNA hybridization showed seven highly conserved type 1 fimbria genes (orf1- to -6 and fimP) in genospecies 1 and 2 strains, except that orf5 and orf3 were divergent in genospecies 1. (ii) In preferential statherin binding, oral Actinomyces viscosus strains of rat and hamster origin (and strain 19246 from a human case of actinomycosis) bound statherin preferentially. DNA hybridization and characterization of the type 1 fimbria genes from strain 19246 revealed a homologous gene cluster of four open reading frames (orfA to -C and fimP). Bioinformatics suggested sortase (orfB, orf4, and part of orf5), prepilin peptidase (orfC and orf6), fimbria subunit (fimP), and usher- and autotransporter-like (orfA and orf1 to -3) functions. Those gene regions corresponding to orf3 and orf5 were divergent, those corresponding to orf2, orf1, and fimP were moderately conserved, and those corresponding to orf4 and orf6 were highly conserved. Restriction fragment length polymorphism analyses using a fimP probe separated human and monkey and rat and hamster strains into phylogenetically different groups. (iii) In statherin-specific binding, strains of A. naeslundii genospecies 1 from septic and other human infections displayed a low-avidity binding to statherin. Only the orf4 and orf6 gene regions were highly conserved. Finally, rat saliva devoid of statherin bound bacterial strains avidly irrespective of ligand specificity, and specific antisera detected either type 1, type 2, or both types of fimbria on the investigated Actinomyces strains.

A novel interaction between type IV pili of Neisseria gonorrhoeae and the human complement regulator C4B-binding protein

C4b-binding protein (C4BP) is an important plasma inhibitor of the classical pathway of complement activation. Several bacterial pathogens bind C4BP, which may contribute to their virulence. In the present report we demonstrate that isolated type IV pili from Neisseria gonorrhoeae bind human C4BP in a dose-dependent and saturable manner. C4BP consists of seven identical alpha-chains and one beta-chain linked together with disulfide bridges. We found that pili bind to the alpha-chain of C4BP, which is composed of eight homologous complement control protein (CCP) domains. From the results of an inhibition assay with C4b and a competition assay in which we tested mutants of C4BP lacking individual CCPs, we concluded that the binding area for pili is localized to CCP1 and CCP2 of the alpha-chain. The binding between pili and C4BP was abolished at 0.25 M NaCl, implying that it is based mostly on ionic interactions, similarly to what have been observed for C4b-C4BP binding. Furthermore, the N-terminal part of PilC, a structural component of pili, appeared to be responsible for binding of C4BP. Membrane cofactor protein, previously shown to be a receptor for pathogenic N. gonorrhoeae on the surface of epithelial cells, competed with C4BP for binding to pili only at high concentrations, suggesting that different parts of pili are involved in these two interactions. Accordingly, high concentrations of C4BP were required to inhibit binding of N. gonorrhoeae to Chang conjunctiva cells, and no inhibition of binding was observed with cervical epithelial cells.

Identification of type 4 fimbriae in Actinobacillus pleuropneumoniae

Type 4 fimbriae have been identified on the cell surface of Actinobacillus pleuropneumoniae by electron microscopy and N-terminal sequencing analysis. A. pleuropneumoniae type 4 fimbrial subunit protein, purified from cell cultures and from outer membrane preparations, reacted with polyclonal antibody raised against type 4 fimbriae of Moraxella bovis on Western blots. N-terminal sequence analysis of the purified 17 kDa type 4 fimbrial subunit protein, named ApfA, revealed the first 12 amino acids to be identical to those of other type 4 fimbrial subunit proteins.

Identification of the F17 fimbrial subunit- and adhesin-encoding (f17A and f17G) gene variants in necrotoxigenic Escherichia coli from cattle, pigs and humans

Putative colonization factors of the F17 family of fimbrial adhesins have been identified in necrotoxigenic Escherichia coli Type 1 and Type 2 (NTEC1 and NTEC2) from calves, pigs, and humans. The f17A and f17G gene variants, coding respectively for the major subunit and for the adhesin of the F17 fimbriae, were typed in 70 E. coli carrying f17-related sequences (15 NTEC1, 51 NTEC2, and four non-NTEC) by colony hybridisation with gene probes derived from the different f17A gene variants (a, b, c, and d) and by PCRs specific for each f17A and f17G (I and II) gene variants. Typing of f17A genes was not possible by colony hybridisation, as most 70 E. coli were positive with more than one gene probe. On the other hand, the PCRs allowed the typing of the f17A gene in 37 E. coli and of the f17G gene in all 70 E. coli. The f17Ab gene variant was detected in 13 NTEC2; the f17Ac, in all 15 NTEC1, six NTEC2 and two non-NTEC; and the f17Ad, in one non-NTEC. Seven additional NTEC2 were positive with the PCRs for two variants: f17Ab and f17Ac in three of them; f17Ac and f17Ad in four of them. Either these seven NTEC2 harbour two variants or the variant present can be detected by two PCRs. The remaining 25 NTEC2 and one non-NTEC tested negative with the PCRs for the four f17A gene variants, suggesting the existence of other variant(s). In contrast, all 70 E. coli were positive with the PCR for the f17GII gene variant and none with the PCR for the f17GI gene variant. The f17-related sequences were present on the CNF2/Vir plasmids in 27 out of the 46 NTEC2 from which plasmid DNA could be extracted: all but one of those positive for the f17Ab gene variant and various proportions of those positive for other variants. In contrast, no plasmid carried f17-related sequences in NTEC1 and non-NTEC.

The F4 fimbrial antigen of Escherichia coli and its receptors

F4 or K88 fimbriae are long filamentous polymeric surface proteins of enterotoxigenic Escherichia coli (ETEC), consisting of so-called major (FaeG) and minor (FaeF, FaeH, FaeC, and probably FaeI) subunits. Several serotypes of F4 have been described, namely F4ab, F4ac, and F4ad. The F4 fimbriae allow the microorganisms to adhere to F4-specific receptors present on brush borders of villous enterocytes and consequently to colonize the small intestine. Such ETEC infections are responsible for diarrhea and mortality in neonatal and recently weaned pigs. In this review emphasis is put on the morphology, genetic configuration, and biosynthesis of F4 fimbriae. Furthermore, the localization of the different a, b, c, and d epitopes, and the localization of the receptor binding site on the FaeG major subunit of F4 get ample attention. Subsequently, the F4-specific receptors are discussed. When the three variants of F4 (F4ab, F4ac, and F4ad) are considered, six porcine phenotypes can be distinguished with regard to the brush border adhesiveness: phenotype A binds all three variants, phenotype B binds F4ab and F4ac, phenotype C binds F4ab and F4ad, phenotype D binds F4ad, phenotype E binds none of the variants, and phenotype F binds F4ab. The following receptor model is described: receptor bcd is found in phenotype A pigs, receptor bc is found in phenotype A and B pigs, receptor d is found in phenotype C and D pigs, and receptor b is found in phenotype F pigs. Furthermore, the characterization of the different receptors is described in which the bcd receptor is proposed as collection of glycoproteins with molecular masses ranging from 45 to 70 kDa, the bc receptor as two glycoproteins with molecular masses of 210 an 240 kDa, respectively, the b receptor as a glycoprotein of 74 kDa, and the d receptor as a glycosphingolipid with unknown molecular mass. Finally, the importance of F4 fimbriae and their receptors in the study of mucosal immunity in pigs is discussed.

Genotypic prevalence of F4 variants (ab, ac, and ad) in Escherichia coli isolated from diarrheic piglets in Korea

A total of 812 Escherichia coli strains isolated from diarrheic piglets were tested for the presence of the F4 (K88) variant (ab, ac and ad) gene by the polymerase chain reaction. Forty four (5.4%) of the 812 E. coli strains carried genes for F4. Among the 44 isolates known to carry genes for F4, 42 (96%) isolates contained genes for F4ac and 2 (4%) isolates contained genes for F4ab. None of the E. coli strains carried genes for F4ad. Our data show that F4ac is the predominant F4 variant associated with diarrhea in piglets in Korea.

A study of relationships among F17 a producing enterotoxigenic and non-enterotoxigenic Escherichia coli strains isolated from diarrheic calves

We investigated the clonal relationships among 41 enterotoxigenic (ETEC) or non-enterotoxigenic (NETEC) Escherichia coli strains producing the F17 a fimbriae isolated from diarrheic calves in France or Belgium in the early 1980s. Twenty-three of the 26 ETEC strains were highly clonally related, most of them with a O101:K32:H9-serotype. The NETEC strains were also divided in clonal subgroups, most of them with O101:H-serotype. The F17 a positive ETEC strains are no longer isolated from diarrheic calves in these countries. It is postulated that the use of a vaccine including O101, K32 and H9 antigens in addition to K99 (F5) explains the strongly reduced isolation of the O101:K32:H9, K99 (F5) E. coli clone.

Characterisation of a type IV pilus produced by Aeromonas caviae

A pilus produced by a clinical isolate of Aeromonas caviae (strain CA195) was purified and partially characterised. The Mr of the pilin was estimated to be 23 kDa by SDS-PAGE. Its N-terminal amino-acid sequence showed that it was closely related to 'bundle-forming' type IV pili purified from other Aeromonas spp. associated with gastro-enteritis and considered to be important intestinal colonisation factors. Bundle-forming pili, often with a polar location, were seen on the surface of strain CA195 which was highly adherent to HEp-2 cells. Removal of surface structures by mechanical means decreased adhesion (by > or = 50%) suggesting that these pili played some role in HEp-2 cell binding. This pilus type could prove an important marker for enteropathogenic A. caviae which appear to lack other putative virulence factors.

tRNA(Arg) (fimU) and expression of SEF14 and SEF21 in Salmonella enteritidis

A Tn10 insertion affecting SEF14 fimbrial synthesis in Salmonella enteritidis was located 13 bp upstream of a gene designated fimU. The 77-bp DNA sequence of fimU from S. enteritidis was identical to that of fimU encoding tRNA(Arg) (UCU) from Salmonella typhimurium and 96% identical to that of the Escherichia coli argU homolog. Furthermore, the open reading frame adjacent to and overlapping the 3' end of fimU was similar to the prophage DLP12 integrase gene. The fimU-encoded transcript comigrated with total cellular tRNA and was predicted to form a tRNA-like cloverleaf structure containing the arginine anticodon UCU. Thus, fimU encoded a tRNA(Arg) specific for the rare codon AGA. fimU mapped to the SEF21 fim operon located 15 C's from the sef14 gene cluster. Although fimU was located within the SEF21 fim gene cluster, the fimU Tn10 insertion mutant of S. enteritidis was found to be defective in SEF14 as well as SEF21 (type 1) fimbria production. SEF17 and SEF18 fimbria production was not affected. Complementation of this mutant with plasmid-borne fimU restored normal production of the fimbrins SefA and FimA as well as their respective fimbriae SEF14 and SEF21. This is the first description of tRNA simultaneously controlling the production of two distinct fimbriae.

Longus pilus of enterotoxigenic Escherichia coli and its relatedness to other type-4 pili--a minireview

Longus is a long pilus produced by human enterotoxigenic Escherichia coli (ETEC) which shares significant structural and biochemical features with class-B type-4 pili. These pili include the toxin-coregulated pilus (TCP) of Vibrio cholerae, the bundle-forming pilus (BFP) of enteropathogenic E. coli and both longus and the colonization factor antigen III (CFA/III) of ETEC. These pili are produced under defined growth conditions indicating that they are under the control of different regulatory elements. While TCP is chromosomally encoded, the remaining pili are encoded on large virulence plasmids. Longus and CFA/III are closely related pili although certain DNA and protein differences also exist between them. This may account for the differences in the regulation, surface presentation, antigenicity, and prevalence of these two pilins among ETEC. Neighboring lngA, a second open reading frame termed lngB was found which encodes a protein with significant homology to proteins which are part of a type-II secretory system such as XcpV, OutC, and PulO of Pseudomonas aeruginosa, Erwinia chrysanthemi, and Klebsiella pneumoniae, respectively. This suggests that lngB may be an accessory gene involved in biogenesis of longus.

Correlation of Pseudomonas aeruginosa virulence factors from clinical and environmental isolates with pathogenicity in the neutropenic mouse

The potential pathogenicity of a microorganism is a major concern for Health Canada evaluators, who will be processing new biotechnology products under the Canadian Environmental Protection Act. Potential pathogenicity is generally predicted by the results of animal pathogenicity studies. In an attempt to define surrogate data for an animal model, this study was initiated. Pseudomonas aeruginosa isolates from clinical and environmental sources were screened for their pilus type, serotype, lipopolysaccharide type, ability to evade host responses, and production of toxin A, exoenzyme S, elastase, phospholipase C, and total protease. The 50% lethal dose (LD50) of the same isolates was determined in the neutropenic mouse model of infection. An attempted correlation was drawn between each (or combinations) of the virulence determinants and the LD50. Stepwise linear regression showed that the presence of high levels of exoenzyme S in association with elastase or phospholipase C, or to a minor extent toxin A, was correlated with low numbers of bacteria required to elicit an LD50. No correlation between any of the other factors examined and virulence was detected. The data suggest that an in vitro high level of exoenzyme S production could be used as surrogate information for neutropenic mouse modelling; however, the levels of all of the extracellular enzymes should be considered when making such an assessment.

Bacterial attachment to uro-epithelial cells: mechanisms and consequences

Microbial attachment to mucosal surfaces is a first step in mucosal infection. Specific interactions between microbial surface ligands and host receptors influence the distribution of microbes in their sites of infection. Adhesion has often been regarded as a sufficient end point, explaining tissue tropism and bacterial persistence at mucosal sites. Adherence, however, is also a virulence factor through which microbes gain access to host tissues, upset the integrity of the mucosal barrier, and cause disease. The induction of mucosal inflammation is one aspect of this process. Bacterial attachment to mucosal surfaces activates the production of pro-inflammatory cytokines that cause both local and systemic inflammation. Epithelial cells are one source of these cytokines. The binding of fimbrial lectins to epithelial cell receptors triggers transmembrane signaling events that upregulate cytokine-specific mRNA and increase cytokine secretion. P fimbriae that bind the globoseries of glycolipids cause the release of ceramides and activation of the ceramide signaling pathway which contributes to the IL-6 response. Spread of cytokines and other pro-inflammatory mediators from the local site contributes to the symptoms and signs of infection.

Identification, purification, and characterization of the type 4 fimbriae of Pasteurella multocida

The presence of fimbriae on Pasteurella multocida has been reported, but there have been no prior studies aimed at conclusively characterizing these structures. We now report on the identification and characterization of type 4 fimbriae on serogroup A, B, and D strains of P. multocida. Under microaerophilic conditions P. multocida showed an increased expression of the fimbriae, which were observed to form bundles. Fimbriae purified by high-performance reverse-phase liquid chromatography constituted a single 18-kDa subunit, the first 21 amino acids of which shared very high similarity with the N-terminal amino acid sequence of other type 4 fimbrial subunits. Antiserum against the P. multocida 18-kDa protein immunostained the type 4 fimbrial subunit of Moraxella bovis and Dichelobacter nodosus. Based on these observations we conclude that P. multocida possesses type 4 fimbriae and have designated the P. multocida fimbrial subunit PtfA.

The molecular genetics of type-4 fimbriae in Pseudomonas aeruginosa--a review

Type-4 fimbriae (or pili) are filaments found at the poles of a wide range of bacterial pathogens, including Neisseria gonorrhoeae, Moraxella bovis, Dichelobacter nodosus and Pseudomonas aeruginosa. They are composed of a small subunit which is highly conserved among different species and appear to mediate adhesion and translocation across epithelial surfaces via a phenomenon termed "twitching motility'. These fimbriae are key host colonisation factors and important protective antigens. We have analysed the genetics and biosynthesis of type-4 fimbriae in P. aeruginosa, which is an opportunistic pathogen of compromised individuals, including those suffering cystic fibrosis, AIDS or burns. A library of P. aeruginosa transposon mutants was constructed which exhibited loss of twitching motility, as determined by altered colony morphology. Analysis of these mutants, and of similar collections by other groups, have revealed that there are at least 22 genes involved in type-4 fimbrial assembly and function. A large number (pilA, B, C, D, E, M, N, O, P, Q, T, U, V and Z) appear to be involved in the biogenesis of the fimbriae and to represent a subset of a supersystem involved in the assembly of surface-associated protein complexes. Homologs of at least some of these genes have subsequently been identified in other type-4 fimbriate bacteria. In P. aeruginosa, the system is also regulated via two signal transduction pathways-a classic sensor-regulator system (encoded by pilS, pilR and rpoN) which controls transcription of the fimbrial subunit, presumably in response to host cues, and a chemotactic system (encoded by pilG, H, I, J, K and L) which may be involved in the directional or rate control of twitching motility in response to local environmental variables.

Colonization factors of human enterotoxigenic Escherichia coli (ETEC)

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of childhood and travellers' diarrhoea. The ability of ETEC to adhere to the intestinal epithelium of the host is an important virulence determinant, and adhesion is mediated by proteinaceous surface appendages called colonization factors.

Salmonella fimbriae: novel antigens in the detection and control of salmonella infections

Fimbriae are thin, proteinaceous surface organelles produced by members of the Enterobacteriaceae, including most salmonellas. A number of fimbrial antigens expressed by strains of Salmonella enteritidis and S. typhimurium have now been described and characterized. However, their functions are still poorly understood, although some evidence indicates they have a role in bacterial survival in the host or external environment. Diagnostic tests based on the detection of fimbriae or specific antibodies against them have recently been developed and applied successfully to the rapid and specific identification of S. enteritidis infections. The role of salmonella fimbriae in future generations of live vaccines either as protective antigens or as the carriers of heterologous antigens is also discussed.

Presence of F107, 2134P and Av24 fimbriae on strains of Escherichia coli isolated from Swedish piglets with diarrhoea

A total of 109 Escherichia coli isolates from piglets with diarrhoea, that had previously been shown to be enterotoxin producers, but negative for the adhesive fimbriae K88, K99, 987P and F41 were tested for the presence of more recently characterised fimbriae. Testing was done by immunodot assay with absorbed polyclonal antisera against Av24 and F107 fimbriae, and unabsorbed polyclonal antiserum and monoclonal antiserum against 2134P fimbriae. Strains were also tested by polymerase chain reaction for the presence of genes encoding the major subunit of F107 fimbriae. After elimination of possible non-specific reactions, antisera testing produced 10 strains positive with all 4 antisera, 1 strain that reacted with all antisera except F107, 2 strains that reacted with all antisera except the 2134P monoclonal, 3 strains that reacted with 2134P polyclonal and F107 and 2 that reacted with F107 only. The PCR testing confirmed the results of the antisera, but also produced an additional 14 positive strains, giving a total of 30% of the strains tested reacting positively by PCR. Furthermore, all 33 isolates positive by PCR came from pigs that were older than 1 week, which is 45% of the 72 isolates tested which came from older pigs.

Structurally variant classes of pilus appendage fibers coexpressed from Burkholderia (Pseudomonas) cepacia

One or more of five morphologically distinct classes of appendage pili were determined to be peritrichously expressed by Burkholderia (formerly Pseudomonas) cepacia isolated from disparate sources. B. cepacia-encoded cblA pilin gene hybridization-based analysis revealed that one associated class, cable (Cbl) adhesin type IIB. cepacia pili, correlates with epidemically transmitted strains from a single cystic fibrosis (CF) center. When only phenotypic assays were available, correlations between the source and the pilus type were nonetheless observed: filamentous (Fil) type IIIB. cepacia pili correlated with CF-associated nonepidemic isolates, spine (Spn) type IVB. cepacia pili correlated with clinical (non-CF) isolates, and spike (Spk) type VB. cepacia pili correlated with environmental isolates. Further, Cbl, Fil, or Spk pili typically appear as an internal framework for constitutively coexpressed, peritrichously arranged dense mats of fine, curly mesh (Msh) type IB. cepacia pili. Constitutive coexpression of dense mats of Msh type IB. cepacia pili in association with a labyrinth of either Cbl, Fil, or Spk pili suggests possible cooperative pilus interactions mediating adhesion-based colonization in the differing environments from which the strains were isolated. Despite such correlations, phylogenetic analyses indicate that with the exception of the epidemically transmitted clusters of isolates, the remaining B. cepacia strains from the other three sources exhibited an equal degree of genetic relatedness independent of origin. As previously found for Escherichia coli, this discrepancy could be accounted for by selection-driven, in vivo horizontal transfer events between distantly related members of the species B. cepacia, leading to the genetic acquisition of environmentally appropriate adhesion-based colonization pilus operons.

The PapG tip adhesin of P fimbriae protects Escherichia coli from neutrophil bactericidal activity

Compared with Escherichia coli ORN103, a nonfimbriated K-12 strain, P-fimbriated E. coli ORN103/pPAP5 was found to interact poorly with human neutrophils and resist their bactericidal activity in vitro. PapG, the Gal alpha(1-->4)Gal binding moiety located at the distal end of the P fimbrial filament, appeared to be responsible for this effect because an isogenic PapG- mutant, E. coli ORN103/pPAP24, exhibited binding interactions with neutrophils that were similar to nonfimbriated E. coli ORN103. Although no direct evidence is available, the poor adherence mediated by PapG could be related to its electrostatic properties because the isolated PapG protein had a pI of 5.2, which indicated that in the physiological pH range it possessed a net negative charge. Antibodies against PapG overcame the protective effect of PapG and markedly enhanced the interactions of P-fimbriated E. coli with neutrophils resulting in bacterial killing. When a P-fimbriated clinical E. coli strain or its isogenic PapG- derivative was injected into the peritoneal cavities of mice, a similar number of neutrophils was recruited to the site of injection. After 2 h, the number of P-fimbriated E. coli organisms that survived the neutrophil influx in the mouse peritoneum was approximately four times more than the number of surviving PapG- bacteria. This result demonstrates that the PapG protein, which is strategically located at the distal region of the P-fibrillum structure, protects E. coli from the bactericidal action of neutrophils.

Role of antibodies against biotype-specific Vibrio cholerae pili in protection against experimental classical and El Tor cholera

Vibrio cholerae O1, which exists as two biotypes, classical and El Tor, expresses fimbrial antigens called toxin-coregulated pili (TCP) and mannose-sensitive hemagglutinin (MSHA) pili, respectively. We have raised rabbit antisera and monoclonal antibodies against these fimbrial antigens and prepared Fab fragments which possess specific antibodies directed against the respective fimbrial antigens from these antisera. The protective effect of these antibody preparations was studied in the infant mouse cholera model. Antibodies against TCP were able to protect baby mice against challenge with V. cholerae O1 of the classical but not of the El Tor biotype. Similar but reverse biotype differences in protection against challenge with classical and El Tor vibrios were observed when antibodies against MSHA pili were used. The protective effect of V. cholerae O1 antilipopolysaccharide (anti-LPS) antibodies, both alone and in combination with antifimbrial antibodies, was also evaluated. We showed that antibodies to the LPS component also prevented infections with V. cholerae O1. Moreover, our results indicate that antibodies against TCP or MSHA pili and against LPS cooperate at least additively, and possible even synergistically, in protecting baby mice against challenge with group O1 vibrios. These results indicate that TCP and MSHA pili as well as LPS play an important role in the pathogenesis of experimental cholera. We could also demonstrate that antibacterial immunity preventing colonization is biotype specific. Our results might be used for the generation of new oral cholera vaccines including both TCP and MSHA fimbrial antigens.

Structure-function and biogenesis of the type IV pili

Type IV pili are adhesins expressed by a number of diverse gram-negative microorganisms. These pili are related through similarities in the primary amino acid sequences of the structural subunits, a conserved assembly machinery, and a similar mechanism of transcriptional regulation. Type IV pilus assembly is preceded by proteolytic processing and N-methylation of the pilin polypeptide. This process is carried out by a novel bifunctional enzyme PilD, first identified in Pseudomonas aeruginosa. Moreover, proteins homologous with type IV pilins have been shown to function in extracellular protein secretion in gram-negative bacteria and in transformation competence in gram-positive microorganisms. Like prepilin, these proteins are also processed and N-methylated by PilD. Transcription of the genes for type IV pilins is carried out by an RNA polymerase with a minor sigma factor, RpoN. In P. aeruginosa two other regulatory elements (PilS and PilR) are required for pilin expression. RpoN, but not PilS and PilR, is required for expression of a diverse set of bacterial genes. Therefore, regulation of synthesis and posttranslational modification and assembly of type IV pili serves as a useful model for a number of diverse biological processes in the bacterial cell.

Variable expression of P fimbriae in Escherichia coli urinary tract infection

Fresh urinary isolates were examined by immunofluorescence with polyclonal rabbit antibodies against type 1 and P fimbriae. This procedure showed P-fimbriate Escherichia coli in 22 of 24 samples from patients with asymptomatic bacteriuria, 24 of 26 samples from patients with cystitis, and 6 of 6 samples from patients with pyelonephritis. Type 1 fimbriae were expressed by less than 40% of isolates in all three groups. There was no relation between the presence of symptoms or the site of infection and fimbrial expression, of P or type 1, by bacteria adherent to freshly isolated uroepithelial cells.

In vivo expression and variation of Escherichia coli type 1 and P pili in the urine of adults with acute urinary tract infections

In vivo expression of pili by Escherichia coli in the urine of 41 adults with lower urinary tract infections was analyzed by immunostaining with polyclonal antiserum to type 1 and P pili. Type 1 pili were detected in 31 of 41 urine specimens, while P pili were detected in 6 of 18 specimens. The piliation status of bacterial populations in urine was heterogeneous, varying from predominantly piliated to a mixture of piliated and nonpiliated cells. Bacteria frequently adhered to exfoliated uroepithelial cells and leukocytes in urine. Expression of pili in vivo did not always correlate with the hemagglutination phenotype after growth in vitro. Strains isolated from different sites in the urogenital tract of two individuals showed phenotypic variation in the state of piliation. The results demonstrate that E. coli type 1 and P pili are expressed and are subject to variation in vivo during acute urinary tract infections in adults.

Analysis of the serum antibody responses to type 1 and type 2 fimbriae in mice immunized with Actinomyces viscosus T14V

The antibody responses of inbred mice immunized with Actinomyces viscosus T14V cells were analyzed using enzyme-linked immunoabsorbent assays (ELISAs) for measuring serum antibodies reactive with A. viscosus T14V cells and type 1 and type 2 fimbriae. In A/J mice immunized intraperitoneally on days 0 and 14, the serum antibody responses approached peak levels during d 19-35, and a dose of 10(8) cells/injection elicited optimal responses. Analysis of the responses of three genetically diverse strains of inbred mice indicated striking variations in the amounts of anti-type 1 (6.5-fold) and anti-type 2 (14.3-fold) antibodies elicited. The observed variations in the magnitude of the anti-fimbrial antibody responses are theoretically of sufficient magnitude to account for significant differences between mouse strains in their ability to inhibit adherence of A. viscosus T14V to saliva-coated hydroxyapatite and other bacteria. These studies provide a model with which the effects of variations in anti-fimbrial antibody responses on bacterial adherence may be analyzed.

Conservation of the D-mannose-adhesion protein among type 1 fimbriated members of the family Enterobacteriaceae

A variety of genera and species of the family Enterobacteriaceae bear surface fimbriae that enable them to bind to D-mannose residues on eukaryotic cells. Until recently, it was thought that the D-mannose binding site was located in the major structural subunit (FimA), of relative molecular mass (Mr) 17,000 (17 K), of these organelles in Escherichia coli. New evidence indicates that this binding site resides instead in a minor protein Mr 28-31 K (FimH) located at the tips and at long intervals along the length of the fimbriae, and is reminiscent of the minor tip adhesion proteins of pyelonephritis-associated pili (Pap) and S fimbriae. In contrast to the antigenic heterogeneity of the major FimA subunit, the antigenic structure of FimH is conserved among different strains of E. coli. Here, we report an even broader conservation of this minor adhesion protein extending to other genera and species of type 1 fimbriated Enterobacteriaceae. Our results may have implications for the development of broadly protective vaccines against Gram-negative bacillary infections in animals and perhaps in man.

Morphological differences in Neisseria meningitidis pili

Disease and carrier isolates of Neisseria meningitidis were examined for their ability to adhere to human buccal epithelial cells and human cell lines and to hemagglutinate human erythrocytes, properties thought to be associated with the presence of pili. Seventy percent (7 of 10) of carrier isolates were found to be highly adherent to human buccal epithelial cells and to agglutinate human A, B, O, Rh-, and Rh+ erythrocytes. In contrast, 60% of the disease isolates adhered poorly to human buccal epithelial cells and 80% failed to agglutinate human erythrocytes. No adherence of either disease or carrier isolates was observed when several human cell lines were tested. When the meningococcal strains were examined by electron microscopy, 7 of 10 disease isolates were found to possess large bundles of aggregated pili (alpha-type pili), while 7 of 10 carrier isolates were found to have numerous unaggregated pili (beta-type pili). A monoclonal antibody against meningococcal pili and one against gonococcal pili reacted with 6 of 10 piliated carrier isolates and 4 of 10 piliated disease isolates. These results suggest that meningococci, like gonococci, possess different types of pili which differ in morphological, antigenic, and binding properties. In addition, antigenic and morphological differences between pili from carrier and disease isolates were observed as well as differences in adherence and hemagglutinating properties.

The use of biochemical markers, serotype and fimbriation in the detection of Escherichia coli clones

Biochemical reactions, O and K serotypes and presence of P-fimbriae were analysed in 116 Escherichia coli strains isolated in blood cultures from patients with bacteraemia and in 99 faecal strains isolated from healthy individuals. By using biochemical typing, the strains could be grouped into six main clusters with similarity index less than 0.8 (Gower, 1971) and altogether 16 subclusters with similarity index 0.82-0.89. The most discriminating tests between the clusters were fermentation of D-tagatose, saccharose, salicin and sorbose. No single biochemical property could differentiate bacteraemic isolates from faecal strains, although strains isolated from blood were significantly more often found in certain subclusters, whereas other subclusters contained mainly control strains. Bacteraemic strains possessed P-fimbriae more often, especially strains isolated from patients with E. coli in the urine concomitantly with bacteraemia. Equally, no single reaction could separate P-fimbriated from non-P-fimbriated strains. D-Tagatose was fermented more often by the P-fimbriated strains; on the other hand, melibiose and lactose fermentation tests were less often positive. Certain O serotypes (O1, O4, O6, O7, O18 and O25) were more common among bacteraemic isolates than controls. K serotypes such as K1, K5 and K52 were also more frequent among blood isolates. We conclude that a combination of biochemical tests, fimbriation and serotyping might be used to identify potentially pathogenic clusters of E. coli.

Differences in adhesiveness among type 1 fimbriate strains of Enterobacteriaceae revealed by an in vitro HEp2 cell adhesion model

Ten type 1 fimbriate strains of Enterobacteriaceae were examined in an in vitro adhesion assay with HEp2 epithelial cells. The range of HEp2 cell adhesiveness, which was characteristic for each strain, was affected by motility, type 1 fimbriation and production of mannose sensitive haemagglutinin. Nevertheless, not all type 1 fimbriate strains adhered well in this model. The findings are discussed with regard to the possibility that different type 1 fimbriate enterobacteria, though all are mannose sensitive, recognize different mannose-containing receptors present or available on the surfaces of the HEp2 cells.

Characterization of Escherichia coli wild-type strains by means of agglutination with antisera raised against cloned P-, S-, and MS-fimbriae antigens, hemagglutination, serotyping and hemolysin production

E. coli strains isolated from patients with urinary tract infections (UTI) very often possess mannose-sensitive (MS) and mannose-resistant (MR) adherence factors (fimbriae). According to their receptor specificity the mannose-resistant adhesins can be divided into several types, P, S, M and X. We have cloned the determinants of three groups of UTI E. coli adhesins, MS, P and S, and prepared specific antisera against the fimbriae antigens. 189 hemagglutination (HA+)-positive strains, 96 fecal isolates and 93 strains isolated from UTI have been tested with these specific antisera and further characterized by receptor specific HA, HA patterns and further of the "common O serogroups" 01, 02, 04, 06, 07, 08, 018, 025, 075, most prevalent in UTI, and hemolysin production. 68 (73%) of the UTI strains and 50 (52%) of the fecal isolates showed P-receptor specificity; 16 (17%) of the uropathogenic bacteria and 33 (34%) of the fecal strains exhibited S, M or X-fimbriae antigens. 24% of the P-hemagglutinating (P+) strains reacted with P (F8)-specific antiserum. In contrast, more than three quarter of the S+-strains were agglutinated by S-specific antiserum. HA-pattern VI and 018 antigen were found to be associated with P-fimbriae strains, whereas HA-pattern V and VII and the O antigens 02 (M-type), 06 and 018 (S-type) occurred most frequently in P--strains. A high percentage of P-fimbriated strains showed mannose-sensitive hemagglutination and hemolysin production.

Characteristics and function of thick and thin conjugative pili determined by transfer-derepressed plasmids of incompatibility groups I1, I2, I5, B, K and Z

Eleven transfer-derepressed plasmids from incompatibility groups I1, I5, B, K and Z were constructed using the dnaG3 mutant Escherichia coli strain BW86. All were found to determine thin flexible and thick rigid pili constitutively. Immune electron microscopy was used to relate thick and thin pilus serotypes with incompatibility grouping. Mutant plasmids that determined only thick pili constitutively transferred efficiently on an agar surface but not in a liquid, whereas plasmids with both kinds of pili transferred equally well in both environments. A mutant of the IncI2 plasmid R721 determined thin pili constitutively, and thick pili at a repressed level, as indicated by electron microscopy. Experiments with this indicated that thin pili were apparently not involved directly in conjugation but were only used to stabilize mating aggregates.

Carbohydrate-binding sites of the mannose-specific fimbrial lectins of enterobacteria

The combining sites of type 1 fimbrial lectins of various species of enterobacteria were studied by measuring the inhibitory activity of linear and branched oligosaccharides and several glycosides of D-mannose on the agglutination of yeast cells by the organisms. The results showed that all five strains of Escherichia coli tested possessed an elongated combining site best fitting a trisaccharide and including a hydrophobic region. Similar results were obtained with Klebsiella pneumoniae. Within the Salmonella genus, the combining sites of the six species tested were similar, but all differed significantly from those of the E. coli strains. The combining sites of Enterobacter cloacae and Enterobacter agglomerans were different from each other and from those of Salmonella sp. and E. coli. The results suggest that although classified under the general term "mannose-specific," bacterial lectins in the form of type 1 fimbriae on different genera exhibit differences in sugar specificities.

Streptococcus salivarius strains carry either fibrils or fimbriae on the cell surface

Strains of Streptococcus salivarius were screened by negative staining for the presence of surface structures. Two structural subgroups were found, carrying either fibrils or fimbriae, projecting from the cell surface. Eight strains carried a very dense peritrichous array of fibrils of two distinct lengths. Long fibrils had an average length of 175 nm, and short fibrils had an average length of 95 nm. Two strains carried only long fibrils, one strain carried only short fibrils, and another strain carried a lateral tuft of very prominent fibrils of two lengths, with a fibrillar fuzz covering the remainder of the cell surface. In all the strains in which they were present, the long fibrils were unaffected by protease or trypsin treatment. In contrast, the short fibrils were completely digested by protease and partially removed by trypsin. Neither long nor short fibrils were affected structurally by mild pepsin digestion or by lipase. The Lancefield extraction procedure removed both long and short fibrils. These twelve fibrillar strains were therefore divisible into four structural subgroups. Extracts of all the fibrillar strains reacted with group K antiserum. The second main structural subgroup consisted of nine strains of S. salivarius, all of which carried morphologically identical, flexible fimbriae arranged peritrichously over the cell surface. The fimbriae were structurally distinct from fibrils and measured 0.5 to 1.0 micron long and 3 to 4 nm wide, with an irregular outline and no obvious substructure. There was no obvious reduction in the number of fimbriae after protease or trypsin treatment. Extracts of the fimbriated strains did not react with the group K antiserum. The two serological and structural subgroups could also be distinguished by colony morphology.