Characterization of FimH adhesins expressed by Salmonella enterica serovar Gallinarum biovars Gallinarum and Pullorum: reconstitution of mannose-binding properties by single amino acid substitution

Glycan-mediated adhesion mechanisms in antibiotic-resistant bacteria

Bacterial adhesins play a central role in host-pathogen interactions, with many specifically targeting glycans to mediate bacterial colonization, influence infection dynamics, and evade host immune responses. In this review, we focus on bacterial pathogens identified by the World Health Organization as critical threats to public health and in urgent need of new treatments. We summarize glycoconjugate targets identified in the literature across 19 bacterial genera and species. This comprehensive review provides a foundation for the development of innovative therapeutic strategies to effectively combat these pathogens.

It takes two to attach - endo-1,3-β-d-glucanase as a potential receptor of mannose-independent, FimH-dependent Salmonella Typhimurium binding to spinach leaves

Currently, fresh, unprocessed food has become a relevant element of the chain of transmission of enteropathogenic infections. To survive on a plant surface and further spread the infections, pathogens like Salmonella have to attach stably to the leaf surface. Adhesion, driven by various virulence factors, including the most abundant fim operon encoding type 1 fimbriae, is usually an initial step of infection, preventing physical removal of the pathogen. Adhesion properties of Salmonella's type 1 fimbriae and its FimH adhesin were investigated intensively in the past. However, there is a lack of knowledge regarding its role in interaction with plant cells. Understanding the mechanisms and structures involved in such interaction may facilitate efforts to decrease the risk of contamination and increase fresh food safety. Here, we applied Salmonella genome site-directed mutagenesis, adhesion assays, protein-protein interactions, and biophysics methods based on surface plasmon resonance to unravel the role of FimH adhesin in interaction with spinach leaves. We show that FimH is at least partially responsible for Salmonella binding to spinach leaves, and this interaction occurs in a mannose-independent manner. Importantly, we identified a potential FimH receptor as endo-1,3-β-d-Glucanase and found that this interaction is strong and specific, with a dissociation constant in the nanomolar range. This research advances our comprehension of Salmonella's interactions with plant surfaces, offering insights that can aid in minimizing contamination risks and improving the safety of fresh, unprocessed foods.

A Review of the Mechanisms of Bacterial Colonization of the Mammal Gut

A healthy animal intestine hosts a diverse population of bacteria in a symbiotic relationship. These bacteria utilize nutrients in the host's intestinal environment for growth and reproduction. In return, they assist the host in digesting and metabolizing nutrients, fortifying the intestinal barrier, defending against potential pathogens, and maintaining gut health. Bacterial colonization is a crucial aspect of this interaction between bacteria and the intestine and involves the attachment of bacteria to intestinal mucus or epithelial cells through nonspecific or specific interactions. This process primarily relies on adhesins. The binding of bacterial adhesins to host receptors is a prerequisite for the long-term colonization of bacteria and serves as the foundation for the pathogenicity of pathogenic bacteria. Intervening in the adhesion and colonization of bacteria in animal intestines may offer an effective approach to treating gastrointestinal diseases and preventing pathogenic infections. Therefore, this paper reviews the situation and mechanisms of bacterial colonization, the colonization characteristics of various bacteria, and the factors influencing bacterial colonization. The aim of this study was to serve as a reference for further research on bacteria-gut interactions and improving animal gut health.

Unraveling the role of type 1 fimbriae in Salmonella pathogenesis: insights from a comparative analysis of Salmonella Enteritidis and Salmonella Gallinarum

Significant differences in pathogenicity between Salmonella Enteritidis and Salmonella Gallinarum exist despite the fact that S. Gallinarum is a direct descendant of S. Enteritidis. It was hypothesized that such various properties may be in part the result of differences in structure and functions of type 1 fimbriae (T1Fs). In S. Enteritidis, T1Fs bind to oligomannosidic structures carried by host cell glycoproteins and are called mannose-sensitive T1Fs (MST1F). In S. Gallinarum, T1Fs lost ability to bind such carbohydrate chains, and were named mannose-resistant MRT1Fs (MRT1F). Therefore, the present study was undertaken to evaluate the role of MST1Fs and MRT1Fs in the adhesion, invasion, intracellular survival and cytotoxicity of S. Enteritidis and S. Gallinarum toward chicken intestinal CHIC8-E11cells and macrophage-like HD11 cells. Using mutant strains: S. Enteritidis fimH::kan and S. Gallinarum fimH::kan devoid of T1Fs and in vitro assays the following observations were made. MST1Fs have a significant impact on the chicken cell invasion by S. Enteritidis as MST1F-mediated adhesion facilitates direct and stable contact of bacteria with host cells, in contrast to MRT1Fs expressed by S. Gallinarum. MST1Fs as well as MRT1Fs did not affected intracellular viability of S. Enteritidis and S. Gallinarum. However, absolute numbers of intracellular viable wild-type S. Enteritidis were significantly higher than S. Enteritidis fimH::kan mutant and wild-type S. Gallinarum and S. Gallinarum fimH::kan mutant. These differences, reflecting the numbers of adherent and invading bacteria, underline the importance of MST1Fs in the pathogenicity of S. Enteritidis infections. The cytotoxicity of wild-type S. Enteritidis and its mutant devoid of MST1Fs to HD11 cells was essentially the same, despite the fact that the number of viable intracellular bacteria was significantly lower in the mutated strain. Using HD11 cells with similar number of intracellular wild-type S. Enteritidis and S. Enteritidis fimH::kan mutant, it was found that the lack of MST1Fs did not affect directly the cytotoxicity, suggesting that the increase in cytotoxicity of S. Enteritidis devoid of MST1Fs may be associated with crosstalk between T1Fs and other virulence factors.

Pre-Growth Culture Conditions Affect Type 1 Fimbriae-Dependent Adhesion of Salmonella

Among various fimbrial structures used by Salmonella enterica to colonize host tissues, type 1 fimbriae (T1F) are among the most extensively studied. Although some experiments have shown the importance of T1F in the initial stages of Salmonella infection, their exact role in the infection process is not fully known. We suggested that different outcomes of T1F investigations were due to the use of different pre-infection growth conditions for the induction of the T1F. We utilized qPCR, flow cytometry, and a wide range of adhesion assays to investigate Salmonella Choleraesuis and Salmonella Typhimurium adhesion in the context of T1F expression. We demonstrated that T1F expression was highly dependent on the pre-infection growth conditions. These growth conditions yielded T1F+ and T1F- populations of Salmonella and, therefore, could be a factor influencing Salmonella-host cell interactions. We supported this conclusion by showing that increased levels of T1F expression directly correlated with higher levels of Salmonella adherence to the intestinal epithelial IPEC-J2 cell line.

Adhesive mechanism of different Salmonella fimbrial adhesins

Salmonellosis is a serious threat to human and animal health. Salmonella adhesion to the host cell is an initial and most crucial step in the pathogenesis of salmonellosis. Many factors are involved in the adhesion process of Salmonella infection. Fimbriae are one of the most important factors in the adhesion of Salmonella. The Salmonella fimbriae are assembled in three types of assembly pathways: chaperon-usher, nucleation-precipitation, and type IV fimbriae. These assembly pathways lead to multiple types of fimbriae. Salmonella fimbriae bind to host cell receptors to initiate adhesion. So far, many receptors have been identified, such as Toll-like receptors. However, several receptors that may be involved in the adhesive mechanism of Salmonella fimbriae are still un-identified. This review aimed to summarize the types of Salmonella fimbriae produced by different assembly pathways and their role in adhesion. It also enlisted previously discovered receptors involved in adhesion. This review might help readers to develop a comprehensive understanding of Salmonella fimbriae, their role in adhesion, and recently developed strategies to counter Salmonella infection.

A novel host-adapted strain of Salmonella Typhimurium causes renal disease in olive ridley turtles (Lepidochelys olivacea) in the Pacific

Salmonella spp. are frequently shed by wildlife including turtles, but S. enterica subsp. enterica serovar Typhimurium or lesions associated with Salmonella are rare in turtles. Between 1996 and 2016, we necropsied 127 apparently healthy pelagic olive ridley turtles (Lepidochelys olivacea) that died from drowning bycatch in fisheries and 44 live or freshly dead stranded turtles from the west coast of North and Central America and Hawaii. Seven percent (9/127) of pelagic and 47% (21/44) of stranded turtles had renal granulomas associated with S. Typhimurium. Stranded animals were 12 times more likely than pelagic animals to have Salmonella-induced nephritis suggesting that Salmonella may have been a contributing cause of stranding. S. Typhimurium was the only Salmonella serovar detected in L. olivacea, and phylogenetic analysis from whole genome sequencing showed that the isolates from L. olivacea formed a single clade distinct from other S. Typhimurium. Molecular clock analysis revealed that this novel clade may have originated as recently as a few decades ago. The phylogenetic lineage leading to this group is enriched for non-synonymous changes within the genomic area of Salmonella pathogenicity island 1 suggesting that these genes are important for host adaptation.

Everything You Always Wanted to Know About Salmonella Type 1 Fimbriae, but Were Afraid to Ask

Initial attachment to host intestinal mucosa after oral infection is one of the most important stages during bacterial pathogenesis. Adhesive structures, widely present on the bacterial surface, are mainly responsible for the first contact with host cells and of host-pathogen interactions. Among dozens of different bacterial adhesins, type 1 fimbriae (T1F) are one of the most common adhesive organelles in the members of the Enterobacteriaceae family, including Salmonella spp., and are important virulence factors. Those long, thin structures, composed mainly of FimA proteins, are responsible for recognizing and binding high-mannose oligosaccharides, which are carried by various glycoproteins and expressed at the host cell surface, via FimH adhesin, which is presented at the top of T1F. In this review, we discuss investigations into the functions of T1F, from the earliest work published in 1958 to operon organization, organelle structure, T1F biogenesis, and the various functions of T1F in Salmonella-host interactions. We give special attention to regulation of T1F expression and their role in binding of Salmonella to cells, cell lines, organ explants, and other surfaces with emphasis on biofilm formation and discuss T1F role as virulence factors based on work using animal models. We also discuss the importance of allelic variation in fimH to Salmonella pathogenesis, as well as role of FimH in Salmonella host specificity.

Bovine colostrum-driven modulation of intestinal epithelial cells for increased commensal colonisation

Nutritional intake may influence the intestinal epithelial glycome and in turn the available attachment sites for bacteria. In this study, we tested the hypothesis that bovine colostrum may influence the intestinal cell surface and in turn the attachment of commensal organisms. Human HT-29 intestinal cells were exposed to a bovine colostrum fraction (BCF) rich in free oligosaccharides. The adherence of several commensal bacteria, comprising mainly bifidobacteria, to the intestinal cells was significantly enhanced (up to 52-fold) for all strains tested which spanned species that are found across the human lifespan. Importantly, the changes to the HT-29 cell surface did not support enhanced adhesion of the enteric pathogens tested. The gene expression profile of the HT-29 cells following treatment with the BCF was evaluated by microarray analysis. Many so called "glyco-genes" (glycosyltransferases and genes involved in the complex biosynthetic pathways of glycans) were found to be differentially regulated suggesting modulation of the enzymatic addition of sugars to glycoconjugate proteins. The microarray data was further validated by means of real-time PCR. The current findings provide an insight into how commensal microorganisms colonise the human gut and highlight the potential of colostrum and milk components as functional ingredients that can potentially increase commensal numbers in individuals with lower counts of health-promoting bacteria.

Fimbriae and related receptors for Salmonella Enteritidis

Infection with Salmonella Enteritidis (SE) is one of the main causes for food- and water-borne diseases, and is a major concern to public health for both humans and animals worldwide. Some fimbrial antigens expressed by SE strains have been described and characterized, containing SEF14, SEF17, SEF21, long polar fimbriae and plasmid-encoded fimbriae, they play a role in bacterial survival in the host or external environment. However, their functions remain to be well elucidated, with the initial attachment and binding for fimbriae-mediated SE infections only minimally understood. Meanwhile, host-pathogen interactions provide insights into receptor modulation of the host innate immune system. Therefore, to well understand the pathogenicity of SE bacteria and to comprehend the host response to infection, the host cell-SE interactions need to be characterized. This review describes SE fimbriae receptors with an emphasis on the interaction between the receptor and SE fimbriae.

Adhesion of Salmonella to Pancreatic Secretory Granule Membrane Major Glycoprotein GP2 of Human and Porcine Origin Depends on FimH Sequence Variation

Bacterial host tropism is a primary determinant of the range of host organisms they can infect. Salmonella serotypes are differentiated into host-restricted and host-adapted specialists, and host-unrestricted generalists. In order to elucidate the underlying molecular mechanisms of host specificity in Salmonella infection, we investigated the role of the intestinal host cell receptor zymogen granule membrane glycoprotein 2 (GP2), which is recognized by FimH adhesin of type 1 fimbriae found in Enterobacteriaceae. We compared four human and two porcine GP2 isoforms. Isoforms were expressed in Sf9 cells as well as in one human (HEp-2) and one porcine (IPEC-J2) cell line. FimH genes of 128 Salmonella isolates were sequenced and the 10 identified FimH variants were compared regarding adhesion (static adhesion assay) and infection (cell line assay) using an isogenic model. We expressed and characterized two functional porcine GP2 isoforms differing in their amino acid sequence to human isoforms by approximately 25%. By comparing all isoforms in the static adhesion assay, FimH variants were assigned to high, low or no-binding phenotypes. This FimH variant-dependent binding was neither specific for one GP2 isoform nor for GP2 in general. However, cell line infection assays revealed fundamental differences: using HEp-2 cells, infection was also FimH variant-specific but mainly independent of human GP2. In contrast, this FimH variant dependency was not obvious using IPEC-J2 cells. Here, we propose an alternative GP2 adhesion/infection mechanism whereby porcine GP2 is not a receptor that determined host-specificity of Salmonella. Salmonella specialists as well as generalists demonstrated similar binding to GP2. Future studies should focus on spatial distribution of GP2 isoforms in the human and porcine intestine, especially comparing health and disease.

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

The Typhi colonization factor (Tcf) is encoded by multiple non-typhoidal Salmonella serovars but exhibits a varying expression profile and interchanging contribution to intestinal colonization

Salmonella enterica serovars Typhi and Paratyphi A are human-restricted pathogens and the leading causative agents of enteric fever. The Typhi colonization factor (Tcf) is a chaperone-usher fimbria, thought to play a role in the host-specificity of typhoidal serovars. Here we show that the tcf cluster (tcfABCD tinR tioA) is present in at least 25 non-typhoidal Salmonella (NTS) serovars and demonstrate its native expression in clinically-important serovars including Schwarzengrund, 9,12:l,v:-, Choleraesuis, Bredeney, Heidelberg, Montevideo, Virchow and Infantis. Although the genetic organization of the tcf cluster is well conserved, the N-terminal half of the fimbrial adhesin, TcfD is highly diverse, suggesting different binding properties of distinct tcfD variants. Comparison of tcfA expression in typhoidal and NTS serovars demonstrated unexpected differences in its expression profiles, with the highest transcription levels in S. Typhi, S. Choleraesuis and S. Infantis. In the latter, tcf is induced in rich broth and under microaerobic conditions, characterizing the intestines of warm blooded animals. Furthermore, Tcf is negatively regulated by the ancestral leucine-responsive transcriptional regulator (Lrp). Using the colitis mouse model, we demonstrate that during mice infection tcfA is expressed at higher levels by S. Infantis than S. Schwarzengrund or S. Heidelberg. Moreover, while Tcf is dispensable for S. Schwarzengrund and S. Heidelberg mouse colonization, Tcf is involved in cecum and colon colonization by S. Infantis. Taken together, our results establish that Tcf is broadly encoded by multiple NTS serovars, but presents variable expression profiles and contributes differently to their virulence.

The Possible Influence of Non-synonymous Point Mutations within the FimA Adhesin of Non-typhoidal Salmonella (NTS) Isolates in the Process of Host Adaptation

Non-typhoidal Salmonella (NTS) remains a global pathogen that affects a wide range of animal species. We analyzed a large number of NTS isolates of different host origins, including Salmonella Heidelberg (n = 80, avian), S. Dublin (50, bovine), S. Typhimurium var 5- (n = 40, porcine), S. 4,5,12,:i:- (n = 40, porcine), S. Cerro (n = 16, bovine), and S. Montevideo (n = 14, bovine), using virulence profiling of the bcfC, mgtC, ssaC, invE, pefA, stn, sopB, and siiE virulence-associated genes, a biofilm production assay, pulsed field gel electrophoresis, and the full-length sequencing of the fimA (adhesin) and iroN (receptor) genes. We determined a key amino acid substitution, A169 (i.e., threonine changed to alanine at position 169), in the FimA protein that changed ligand affinity of FimA toward N-acetyl-D-glucosamine. This finding clearly indicates the important role of non-synonymous single nucleotide polymorphism (nsSNPs) in adhesin functionality that may impact the host tropism of NTS. This nsSNP was found in S. Heidelberg and S. Cerro isolates. Although this was not the case for the IroN receptor, the phylogeny of this receptor and different host origins of NTS isolates were positively correlated, suggesting existence of specific host immune selective pressures on this unique receptor in S. enterica. We found that pefA, a gene encoding major fimbrial subunit, was the most-segregative virulence factor. It was associated with S. Heidelberg, S. Typhimurium var 5- and S. 4,5,12,:i:- but not with the rest of NTS strains. Further, we observed a significantly higher frequency of non-biofilm producers among NTS strains that do not carry pefA (42.5%) compared to S. Heidelberg (2.5%) and S. Typhimurium var 5- (7.5%) and S. 4,5,12,:i:- (0%). This study provides new insights into the host adaptation of avian and mammalian NTS isolates that are based on the bacterial antigens FimA and IroN as well as the interrelationships between host adaptation, overall genetic relatedness, and virulence potential in these NTS isolates.

The plasmid-encoded Ipf and Klf fimbriae display different expression and varying roles in the virulence of Salmonella enterica serovar Infantis in mouse vs. avian hosts

Salmonella enterica serovar Infantis is one of the prevalent Salmonella serovars worldwide. Different emergent clones of S. Infantis were shown to acquire the pESI virulence-resistance megaplasmid affecting its ecology and pathogenicity. Here, we studied two previously uncharacterized pESI-encoded chaperone-usher fimbriae, named Ipf and Klf. While Ipf homologs are rare and were found only in S. enterica subspecies diarizonae and subspecies VII, Klf is related to the known K88-Fae fimbria and klf clusters were identified in seven S. enterica subspecies I serovars, harboring interchanging alleles of the fimbria major subunit, KlfG. Regulation studies showed that the klf genes expression is negatively and positively controlled by the pESI-encoded regulators KlfL and KlfB, respectively, and are activated by the ancestral leucine-responsive regulator (Lrp). ipf genes are negatively regulated by Fur and activated by OmpR. Furthermore, induced expression of both klf and ipf clusters occurs under microaerobic conditions and at 41°C compared to 37°C, in-vitro. Consistent with these results, we demonstrate higher expression of ipf and klf in chicks compared to mice, characterized by physiological temperature of 41.2°C and 37°C, respectively. Interestingly, while Klf was dispensable for S. Infantis colonization in the mouse, Ipf was required for maximal colonization in the murine ileum. In contrast to these phenotypes in mice, both Klf and Ipf contributed to a restrained infection in chicks, where the absence of these fimbriae has led to moderately higher bacterial burden in the avian host. Taken together, these data suggest that physiological differences between host species, such as the body temperature, can confer differences in fimbriome expression, affecting Salmonella colonization and other host-pathogen interplays.

The Novel Type 1 Fimbriae FimH Receptor Calreticulin Plays a Role in Salmonella Host Specificity

It was suggested that minor differences in the structure of FimH are most likely associated with differences in its adhesion specificities and may determine the tropism of various Salmonella serovars to different species and tissues. We have recently shown that FimH adhesins from host-adapted serovars, e.g., Salmonella Choleraesuis (SCh), bind to other glycoprotein receptors compared to FimH from host-unrestricted Salmonella Enteritidis (SE). Here we identify porcine calreticulin expressed by swine intestinal cells as a host-specific receptor for SCh FimH adhesin, suggesting that such an interaction may contribute to SCh host specificity. Calreticulin was identified by 2D electrophoresis and mass spectrometry as a glycoprotein that was bound specifically by recombinant SCh FimH protein, but not by FimH from SE. The functionality of calreticulin as a specific receptor of SCh FimH adhesin was further confirmed by adhesion and invasion of mutated strains of SCh carrying different variants of FimH proteins to IPEC-J2 cells with overexpression and silenced expression of calreticulin. It was found that SCh carrying the active variant of FimH adhered and invaded IPEC-J2 cells with calreticulin overexpression at significantly higher numbers than those of SCh expressing the non-active variant or SE variant of FimH. Moreover, binding of SCh carrying the active variant of FimH to IPEC-J2 with silenced calreticulin expression was significantly weaker. Furthermore, we observed that SCh infection induces translocation of calreticulin to cell membrane. All of the aforementioned results lead to the general conclusion that Salmonella host specificity requires not only special mechanisms and proteins expressed by the pathogen but also specifically recognized receptors expressed by a specific host.

Salmonella Typhimurium Enzymatically Landscapes the Host Intestinal Epithelial Cell (IEC) Surface Glycome to Increase Invasion

Although gut host-pathogen interactions are glycan-mediated processes, few details are known about the participating structures. Here we employ high-resolution mass spectrometric profiling to comprehensively identify and quantitatively measure the exact modifications of native intestinal epithelial cell surface N-glycans induced by S. typhimurium infection. Sixty minutes postinfection, select sialylated structures showed decreases in terms of total number and abundances. To assess the effect of cell surface mannosylation, we selectively rerouted glycan expression on the host using the alpha-mannosidase inhibitor, kifunensine, toward overexpression of high mannose. Under these conditions, internalization of S. typhimurium significantly increased, demonstrating that bacteria show preference for particular structures. Finally, we developed a novel assay to measure membrane glycoprotein turnover rates, which revealed that glycan modifications occur by bacterial enzyme activity rather than by host-derived restructuring strategies. This study is the first to provide precise structural information on how host N-glycans are altered to support S. typhimurium invasion.

The Non-Fimbriate Phenotype Is Predominant among Salmonella enterica Serovar Choleraesuis from Swine and Those Non-Fimbriate Strains Possess Distinct Amino Acid Variations in FimH

Although most Salmonella serovars are able to infect a range of animal hosts, some have acquired the ability to cause systemic infections of specific hosts. For example, Salmonella enterica serovar Choleraesuis is primarily associated with systemic infection in swine. Adherence to host epithelial cells is considered a prerequisite for initial infection, and fimbrial appendages on the outer membrane of the bacteria are implicated in this process. Although type 1 fimbriae encoded by the fim gene cluster are commonly found in Salmonella serovars, it is not known whether S. Choleraesuis produces this fimbrial type and if and how fimbriae are involved in pathogenesis. In the present study, we demonstrated that only four out of 120 S. Choleraesuis isolates from pigs with salmonellosis produced type 1 fimbriae as assayed by the yeast agglutination test and electron microscopy. One of the 116 non-type 1 fimbria-producing isolates was transformed with plasmids carrying different fim genes from S. Typhimurium LB5010, a type 1 fimbria-producing strain. Our results indicate that non-type 1 fimbria-producing S. Choleraesuis required only an intact fimH to regain the ability to produce fimbrial appendages. Sequence comparison revealed six amino acid variations between the FimH of the non-type 1 fimbria-producing S. Choleraesuis isolates and those of the type 1 fimbria-producing S. Choleraesuis isolates. S. Choleraesuis that produced type 1 fimbriae contained FimH with an amino acid sequence identical to that of S. Typhimurium LB5010. Site-directed mutagenesis leading to the replacement of the non-conserved residues revealed that a change from glycine to valine at position of 63 (G63V) resulted in a non-type 1 fimbria-producing S. Choleraesuis being able to express type 1 fimbriae on its outer membrane. It is possible that this particular amino acid change prevents this polypeptide from proper interaction with other Fim subunits required for assembly of an intact type 1 fimbrial shaft in S. Choleraesuis; however, it remains to be determined if and how the absence of type 1 fimbriae production is related to the systemic infection of the swine host by S. Choleraesuis.

Allelic variation contributes to bacterial host specificity

Understanding the molecular parameters that regulate cross-species transmission and host adaptation of potential pathogens is crucial to control emerging infectious disease. Although microbial pathotype diversity is conventionally associated with gene gain or loss, the role of pathoadaptive nonsynonymous single-nucleotide polymorphisms (nsSNPs) has not been systematically evaluated. Here, our genome-wide analysis of core genes within Salmonella enterica serovar Typhimurium genomes reveals a high degree of allelic variation in surface-exposed molecules, including adhesins that promote host colonization. Subsequent multinomial logistic regression, MultiPhen and Random Forest analyses of known/suspected adhesins from 580 independent Typhimurium isolates identifies distinct host-specific nsSNP signatures. Moreover, population and functional analyses of host-associated nsSNPs for FimH, the type 1 fimbrial adhesin, highlights the role of key allelic residues in host-specific adherence in vitro. Together, our data provide the first concrete evidence that functional differences between allelic variants of bacterial proteins likely contribute to pathoadaption to diverse hosts.

One of the key aspects for controlling infectious diseases is understanding how pathogens cross host species. Here the authors conduct a genome-wide analysis of Salmonella and show a high degree of variation, enabling host-adapted colonization among Salmonella intestinal and systemic serovars.

Fimbriae: Classification and Biochemistry

Proteinaceous, nonflagellar surface appendages constitute a variety of structures, including those known variably as fimbriae or pili. Constructed by distinct assembly pathways resulting in diverse morphologies, fimbriae have been described to mediate functions including adhesion, motility, and DNA transfer. As these structures can represent major diversifying elements among Escherichia and Salmonella isolates, multiple fimbrial classification schemes have been proposed and a number of mechanistic insights into fimbrial assembly and function have been made. Herein we describe the classifications and biochemistry of fimbriae assembled by the chaperone/usher, curli, and type IV pathways.

Two specific amino acid variations in colonization factor CS6 subtypes of enterotoxigenic Escherichia coli results in differential binding and pathogenicity

CS6 is the predominant colonization factor of enterotoxigenic Escherichia coli (ETEC). We report the existence of multiple CS6 subtypes caused by natural point mutations in cssA and cssB, the structural genes for CS6. The subtype AIBI was mostly associated with ETEC isolated from diarrhoeal cases, whereas AIIBII was mostly found in asymptomatic controls. Here we explore the rationale behind this association. ETEC isolates expressing AIIBII showed weaker adherence to intestinal epithelial cells compared with ETEC expressing AIBI. AIIBII expression on the ETEC cell surface was threefold less than AIBI. We found that alanine at position 37 in CssAII, in conjunction with asparagine at position 97 in CssBII, was responsible for the decreased levels of AIIBII on the bacterial surface. In addition, purified AIIBII showed fourfold less mucin binding compared with AIBI. The asparagine at position 97 in CssBII was also accountable for the decreased mucin binding by AIIBII. Reduced fluid accumulation and colonization occurred during infection with ETEC expressing AIIBII in animal models. Together these results indicate that the differential adherence between AIBI and AIIBII was a cumulative effect of decreased surface-level expression and mucin binding of AIIBII due to two specific amino acid variations. As a consequence, ETEC expressing these two subtypes displayed differential pathogenicity. We speculate that this might explain the subjective association of AIBI with ETEC from diarrhoeal cases and AIIBII with asymptomatic controls.

Identification of Isolated Salmonella enterica Serotype gallinarum Biotype Pullorum and Gallinarum by PCR-RFLP

Background:

Salmonella spp. is the major bacterial pathogen in poultry and is responsible for significant economic losses of the poultry industry in many parts of the world. Among Salmonella spp., Salmonellagallinarum and Salmonella.pullorum are the most common causative agents of chicken salmonellosis resulting in high mortality and morbidity.

Objectives:

The aim of this study was to identify S. gallinarum and S. pullorum by using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

Materials and Methods:

In this study, 13 samples of Salmonella, isolated from local poultry, were obtained from Razi Type Culture Collection (RTCC). For the PCR-RFLP method based on the fliC gene, extracted DNA was used as a template for amplifying of the fliC gene (197bp) using specific primers. PCR products were subjected to digestion using Hinp1I restriction endonuclease.

Results:

For the PCR, 197 bp fliC fragment was amplified from all 13 isolates. Ten out of 13 were S.gallinarum and the other three were S. pullorum. As part of the PCR-RFLP, two fragments were obtained (82 bp and 115 bp) for all S.gallinarum, whereas no digestion was observed in S. pullorum, and 197 bp fragment was seen.

Conclusions:

PCR-RFLP with fliC gene and Hinp1I endonuclease were successfully applied to differentiate the two biotypes. The results suggested that this technique could be effective in detecting S. gallinarum and S. pullorum.

Allelic variation in Salmonella: an underappreciated driver of adaptation and virulence

Salmonella enterica causes substantial morbidity and mortality in humans and animals. Infection and intestinal colonization by S. enterica require virulence factors that mediate bacterial binding and invasion of enterocytes and innate immune cells. Some S. enterica colonization factors and their alleles are host restricted, suggesting a potential role in regulation of host specificity. Recent data also suggest that colonization factors promote horizontal gene transfer of antimicrobial resistance genes by increasing the local density of Salmonella in colonized intestines. Although a profusion of genes are involved in Salmonella pathogenesis, the relative importance of their allelic variation has only been studied intensely in the type 1 fimbrial adhesin FimH. Although other Salmonella virulence factors demonstrate allelic variation, their association with specific metadata (e.g., host species, disease or carrier state, time and geographic place of isolation, antibiotic resistance profile, etc.) remains to be interrogated. To date, genome-wide association studies (GWAS) in bacteriology have been limited by the paucity of relevant metadata. In addition, due to the many variables amid metadata categories, a very large number of strains must be assessed to attain statistically significant results. However, targeted approaches in which genes of interest (e.g., virulence factors) are specifically sequenced alleviates the time-consuming and costly statistical GWAS analysis and increases statistical power, as larger numbers of strains can be screened for non-synonymous single nucleotide polymorphisms (SNPs) that are associated with available metadata. Congruence of specific allelic variants with specific metadata from strains that have a relevant clinical and epidemiological history will help to prioritize functional wet-lab and animal studies aimed at determining cause-effect relationships. Such an approach should be applicable to other pathogens that are being collected in well-curated repositories.

FimH adhesin from host unrestricted Salmonella Enteritidis binds to different glycoprotein ligands expressed by enterocytes from sheep, pig and cattle than FimH adhesins from host restricted Salmonella Abortus-ovis, Salmonella Choleraesuis and Salmonella Dublin

Adhesion to gut tissues and colonization of the alimentary tract, two important stages in the pathogenesis of Salmonella, are mediated by FimH adhesin of type 1 fimbriae. It was suggested that minor differences in the structure of FimH are most likely associated with differences in adhesion specificities, and may determine the tropism of various Salmonella serovars to different species and tissues. We investigated this hypothesis by comparing the binding properties of FimH proteins from three Salmonella enterica serovars with limited (Choleraesuis, Dublin) or restricted (Abortusovis) host ranges to FimH from broad host range S. Enteritidis and mannose inactive FimH from S. Gallinarum. Although all active variants of FimH protein were able to bind mannose-rich glycoproteins (RNase B, HRP and Man-BSA) with comparable affinity measured by surface plasmon resonance, there were significant differences in the binding profiles of the FimH proteins from host restricted serovars and host unrestricted serovar Enteritidis, to glycoproteins from enterocyte cell lines established in vitro and derived from sheep, pig and cattle. When low-binding FimH adhesin from S. Enteritidis was subjected to Western blot analysis, it bound to surface membrane protein of about 130 kDa, and high-binding FimH adhesins from S. Abortusovis, S. Choleraesuis and S. Dublin bound to surface membrane protein of about 55 kDa present in each cell line. Differential binding of FimH proteins from host-restricted and broad-host-range Salmonella to intestinal receptors was confirmed using mutant FimH adhesins obtained by site-directed mutagenesis. It was found that the low-binding variant of FimH from S. Choleraesuis with mutation Leu57Pro lost the ability to bind protein band of 55 kDa, but instead interacted with glycoprotein of about 130 kDa. On the other hand, the high-binding variant of FimH adhesin from S. Enteritids with mutation Asn101Ser did not bind to its receptor of 130 kDa, but instead it interacted with glycoprotein ligand of 55 kDa. These results suggest that FimH adhesins of type 1 fimbriae are one of the factors responsible for different host-specificities of these Salmonella serovars.

Diversification of the Salmonella fimbriae: a model of macro- and microevolution

Bacteria of the genus Salmonella comprise a large and evolutionary related population of zoonotic pathogens that can infect mammals, including humans and domestic animals, birds, reptiles and amphibians. Salmonella carries a plethora of virulence genes, including fimbrial adhesins, some of them known to participate in mammalian or avian host colonization. Each type of fimbria has its structural subunit and biogenesis genes encoded by one fimbrial gene cluster (FGC). The accumulation of new genomic information offered a timely opportunity to better evaluate the number and types of FGCs in the Salmonella pangenome, to test the use of current classifications based on phylogeny, and to infer potential correlations between FGC evolution in various Salmonella serovars and host niches. This study focused on the FGCs of the currently deciphered 90 genomes and 60 plasmids of Salmonella. The analysis highlighted a fimbriome consisting of 35 different FGCs, of which 16 were new, each strain carrying between 5 and 14 FGCs. The Salmonella fimbriome was extremely diverse with FGC representatives in 8 out of 9 previously categorized fimbrial clades and subclades. Phylogenetic analysis of Salmonella suggested macroevolutionary shifts detectable by extensive FGC deletion and acquisition. In addition, microevolutionary drifts were best depicted by the high level of allelic variation in predicted or known adhesins, such as the type 1 fimbrial adhesin FimH for which 67 different natural alleles were identified in S. enterica subsp. I. Together with strain-specific collections of FGCs, allelic variation among adhesins attested to the pathoadaptive evolution of Salmonella towards specific hosts and tissues, potentially modulating host range, strain virulence, disease progression, and transmission efficiency. Further understanding of how each Salmonella strain utilizes its panel of FGCs and specific adhesin alleles for survival and infection will support the development of new approaches for the control of Salmonellosis.

Evolution of Salmonella enterica virulence via point mutations in the fimbrial adhesin

Whereas the majority of pathogenic Salmonella serovars are capable of infecting many different animal species, typically producing a self-limited gastroenteritis, serovars with narrow host-specificity exhibit increased virulence and their infections frequently result in fatal systemic diseases. In our study, a genetic and functional analysis of the mannose-specific type 1 fimbrial adhesin FimH from a variety of serovars of Salmonella enterica revealed that specific mutant variants of FimH are common in host-adapted (systemically invasive) serovars. We have found that while the low-binding shear-dependent phenotype of the adhesin is preserved in broad host-range (usually systemically non-invasive) Salmonella, the majority of host-adapted serovars express FimH variants with one of two alternative phenotypes: a significantly increased binding to mannose (as in S. Typhi, S. Paratyphi C, S. Dublin and some isolates of S. Choleraesuis), or complete loss of the mannose-binding activity (as in S. Paratyphi B, S. Choleraesuis and S. Gallinarum). The functional diversification of FimH in host-adapted Salmonella results from recently acquired structural mutations. Many of the mutations are of a convergent nature indicative of strong positive selection. The high-binding phenotype of FimH that leads to increased bacterial adhesiveness to and invasiveness of epithelial cells and macrophages usually precedes acquisition of the non-binding phenotype. Collectively these observations suggest that activation or inactivation of mannose-specific adhesive properties in different systemically invasive serovars of Salmonella reflects their dynamic trajectories of adaptation to a life style in specific hosts. In conclusion, our study demonstrates that point mutations are the target of positive selection and, in addition to horizontal gene transfer and genome degradation events, can contribute to the differential pathoadaptive evolution of Salmonella.

Decreased colonization of chicks by Salmonella enterica serovar Gallinarum expressing mannose-sensitive FimH adhesin from Salmonella enterica serovar Enteritidis

To investigate the role of non-hemagglutinating type 1 fimbriae in the pathogenesis of Salmonella Gallinarum, the isogenic mutant elaborating type 1 fimbriae with mannose-sensitive (MS) variant of the FimH adhesin from Salmonella Enteritidis and the mutant strain with no FimH expression were constructed. Their binding to chicken leukocytes in vitro and invasiveness in 1-day-old chicks were studied. Our results demonstrated that S. Gallinarum type 1 fimbriae with an endogenous variant of the FimH adhesin mediated mannose-resistant (MR) binding to avian leukocytes and did not bind to human epithelial cells. However, after allelic replacement of the FimH, mutated fimbriae with S. Enteritidis variant of the FimH adhesin bound to both cell types in a mannose-dependent manner. In chick model, S. Gallinarum expressing wild-type FimH variant colonized cecal tonsils and bursa of Fabricius more effectively and invaded the spleen and liver in greater numbers than S. Gallinarum fimH knockout strain or mutant expressing MS FimH variant from S. Enteritidis. The invasive potential of the latter was greatly reduced in chicks since no viable bacteria expressing MS variant of the adhesin could be recovered from intestinal lymphoid tissues or liver over a 6 days course of infection. Together, these results demonstrate that the S. Gallinarum type 1 fimbriae with the endogenous MR variant of the FimH protein increase systemic dissemination of S. Gallinarum and colonization of internal organs in chicks indicating the importance of these adhesive structures in the virulence of S. Gallinarum.

Single nucleotide polypmorphisms of fimH associated with adherence and biofilm formation by serovars of Salmonella enterica

Type 1 fimbriae produced by serovars of Salmonella are characterized by their ability to agglutinate guinea pig erythrocytes in the absence of d-mannose but not in its presence. The FimH protein is the adhesin that mediates this reaction; it is distinct from the major fimbrial protei.n (FimA) that composes the fimbrial shaft. Avian-adapted serovars of Salmonella produce non-haemagglutinating fimbriae that have been reported to mediate adherence to avian cells. A single amino acid substitution is present in the FimH adhesin of these strains compared to that of a Typhimurium isolate. Also, previous studies have shown that single nucleotide polymorphisms in two strains of the Typhimurium fimH alter the binding specificity. We therefore investigated the allelic variation of fimH from a range of serotypes (both host-adapted and non-host-adapted) and isolates of Salmonella. Most FimH adhesins mediated the mannose-sensitive haemagglutination of guinea pig erythrocytes, but many did not facilitate adherence to HEp-2 cells. A small number of isolates also produced fimbriae but did not mediate adherence to either cell type. Transformants possessing cloned fimH genes exhibited a number of different substitutions within the predicted amino acid sequence of the FimH polypeptide. No identical FimH amino sequence was found between strains that adhere to erythrocytes and/or HEp-2 cells and those produced by non-adherent strains. FimH-mediated adherence to HEp-2 cells was invariably associated with the ability to form biofilms on mannosylated bovine serum albumin.

Allosteric catch bond properties of the FimH adhesin from Salmonella enterica serovar Typhimurium

Despite sharing the name and the ability to mediate mannose-sensitive adhesion, the type 1 fimbrial FimH adhesins of Salmonella Typhimurium and Escherichia coli share only 15% sequence identity. In the present study, we demonstrate that even with this limited identity in primary sequence, these two proteins share remarkable similarity of complex receptor binding and structural properties. In silico simulations suggest that, like E. coli FimH, Salmonella FimH has a two-domain tertiary structure topology, with a mannose-binding pocket located on the apex of a lectin domain. Structural analysis of mutations that enhance S. Typhimurium FimH binding to eukaryotic cells and mannose-BSA demonstrated that they are not located proximal to the predicted mannose-binding pocket but rather occur in the vicinity of the predicted interface between the lectin and pilin domains of the adhesin. This implies that the functional effect of such mutations is indirect and probably allosteric in nature. By analogy with E. coli FimH, we suggest that Salmonella FimH functions as an allosteric catch bond adhesin, where shear-induced separation of the lectin and pilin domains results in a shift from a low affinity to a high affinity binding conformation of the lectin domain. Indeed, we observed shear-enhanced binding of whole bacteria expressing S. Typhimurium type 1 fimbriae. In addition, we observed that anti-FimH antibodies activate rather than inhibit S. Typhimurium FimH mannose binding, consistent with the allosteric catch bond properties of this adhesin.

Adhesive mechanisms of Salmonella enterica

Salmonella enterica is an invasive, facultative intracellular pathogen of animal and man with the ability to colonize various niches in diverse host organisms. The pathogenesis of infections by S. enterica requires adhesion to various host cell surfaces, and a large number of adhesive structures can be found. Depending on the serotype of S. enterica, gene clusters for more than 10 different fimbrial adhesins were identified, with type I fimbriae such as Fim, Lpf (long polar fimbriae), Tafi (thin aggregative fimbriae) or the type IV pili of serotype Typhi. In addition, autotransporter adhesins such as ShdA, MisL and SadA and the type I secreted large repetitive adhesins SiiE and BapA have been identified. Although the functions of many of the various adhesins are not well understood, recent studies show the specific structural and functional properties of Salmonella adhesins and how they act in concert with other virulence determinants. In this chapter, we describe the molecular characteristics of Salmonella adhesins and link these features to their multiple functions in infection biology.

Identification of adhesin–receptor interactions driving bacterial translocation through M cells

Evaluation of: Hase K, Kawano K, Nochi T et al.: Uptake through glycoprotein 2 of FimH+ bacteria by M cells initiates mucosal immune response. Nature 462, 226–230 (2009). M cells are specialized epithelial cells that transport antigens into lymphoid follicles. The mechanisms by which molecules, particles and microorganisms are transported by M cells remains poorly understood. Here, Hase and colleagues move a significant step forward by performing an extensive functional characterization of the GP2 interaction with FimH adhesin of bacterial type 1 pili. They show that GP2 is selectively expressed in M cells and functions as an endocytic receptor for type I-piliated bacteria. Comparison of Salmonella infection of wild-type and GP2-deficient mice confirmed the relevance of the GP2–FimH interaction in triggering an antigen-specific immune response in mice. Although this work supports the idea that the GP2-dependent pathway might constitute a new target for oral vaccine delivery it is necessary to be cautious as the reported enhancement of immune responses associated with GP2 and FimH expression were relatively modest. Since variation in FimH has been reported to have a major impact on glycoprotein binding, it might be possible to improve the efficacy of a putative vaccine using recombinant bacteria expressing high-affinity FimH variants. Alternative adhesin/receptor interactions are also likely to play a role in bacterial sampling by M cells and might also be exploited to enhance vaccine delivery.

The high-adhesive properties of the FimH adhesin of Salmonella enterica serovar Enteritidis are determined by a single F118S substitution

The binding properties of low- and high-adhesive forms of FimH adhesins from Salmonella enterica serovars Enteritidis and Typhimurium (S. Enteritidis and S. Typhimurium) were studied using chimeric proteins containing an additional peptide that represents an N-terminal extension of the FimF protein. This modification, by taking advantage of a donor strand exchange mechanism, closes the hydrophobic groove in the fimbrial domain of the FimH adhesin. Such self-complemented adhesins (scFimH) did not form aggregates and were more stable (resistant to proteolytic cleavage) than native FimH. High-adhesive variants of scFimH proteins, with alanine at position 61 and serine at position 118, were obtained by site-directed mutagenesis of fimH genes from low-adhesive variants of S. Enteritidis and S. Typhimurium, with glycine at position 61 and phenylalanine at position 118. Direct kinetic analysis using surface plasmon resonance (SPR) and glycoproteins carrying high-mannose carbohydrate chains (RNase B, horseradish peroxidase and mannan-BSA) revealed the existence of high- and low-adhesive allelic variants, not only in S. Typhimurium but also in S. Enteritidis. Using two additional mutants of low-adhesive FimH protein from S. Enteritidis (Gly61Ala and Phe118Ser), SPR analysis pointed to Ser118 as the major determinant of the high-adhesive phenotype of type 1 fimbriae from S. Enteritidis. These studies demonstrated for the first time that the functional differences observed with whole fimbriated bacteria could be reproduced at the level of purified adhesin. They strongly suggest that the adhesive properties of type 1 fimbriae are determined only by structural differences in the FimH proteins and are not influenced by the fimbrial shaft on which the adhesin is located.

Mannanoligosaccharide agglutination by Salmonella enterica strains isolated from carrier pigs

Type-1 fimbriae are associated with most Salmonella enterica serovars and are an essential factor for host colonization. Mannanoligosaccharides (MOS), a prebiotic that is agglutinated by type-1 fimbriae, are proposed for the control of enterobacteria colonization and may be an alternative to Salmonella control in pigs. The aim of this study was to evaluate the capability of porcine Salmonella strains to adhere to MOS in vitro. A total of 108 strains of Salmonella sp. isolated from carrier pigs were evaluated for the amplification of fimA and fimH genes, agglutination of MOS and hemagglutination. In all tested strains, amplicons of expected size were detected for both fimA and fimH gene. In the hemagglutination assays, 31 (28.7%) strains presented mannose-sensitive agglutination of erythrocytes, indicating that the strains were expressing type-1 fimbriae. Considering only strains expressing the type-1 fimbriae, 23 (74.2%) presented a strong agglutination of MOS, 3 (9.6%) a weak reaction and 5 (16.2%) none. The results indicate that Salmonella enterica strains expressing type-1 fimbriae can agglutinate effectively in vitro to MOS.

FimH alleles direct preferential binding of Salmonella to distinct mammalian cells or to avian cells

This study aimed to determine whether allelic variants of the FimH adhesin from Salmonella enterica confer differential bacterial binding to different types of mammalian cells [murine bone marrow-derived dendritic cells (DCs) and HEp-2 cells] and chicken leukocytes. Although the type 1 fimbriated S. enterica serovar Typhimurium strains AJB3 (SR-11 derivative) and SL1344 both aggregated yeast cells, only the former bound efficiently to DCs and HEp-2 cells. Type 1 fimbriae-mediated binding to DCs having previously been shown to require the FimH adhesin and to be inhibited by mannose, FimH sequences from strains SL1344 and AJB3 were compared and found to differ by only one residue, asparagine 158 in SL1344 being replaced by a tyrosine in AJB3. The importance of residue 158 for FimH-mediated binding was further confirmed in recombinant Escherichia coli expressing S. enterica type 1 fimbriae with a variety of substitutions engineered at this position. Additional studies with the 'non-adhesive' FimH of a type 2 fimbriated S. enterica serovar Gallinarum showed that this FimH did not mediate bacterial binding to murine DCs or HEp-2 cells. However, the type 2 FimH significantly improved bacterial adhesion to chicken leukocytes, in comparison to the type 1 FimH of strain AJB3, attributing for the first time a function to the type 2 fimbriae of S. enterica. Consequently, our data show that allelic variation of the S. enterica FimH adhesin directs not only host-cell-specific recognition, but also distinctive binding to mammalian or avian receptors. It is most relevant that this allele-specific binding profile parallels the host specificity of the respective FimH-expressing pathogen.

Evolution of the chaperone/usher assembly pathway: fimbrial classification goes Greek

Many Proteobacteria use the chaperone/usher pathway to assemble proteinaceous filaments on the bacterial surface. These filaments can curl into fimbrial or nonfimbrial surface structures (e.g., a capsule or spore coat). This article reviews the phylogeny of operons belonging to the chaperone/usher assembly class to explore the utility of establishing a scheme for subdividing them into clades of phylogenetically related gene clusters. Based on usher amino acid sequence comparisons, our analysis shows that the chaperone/usher assembly class is subdivided into six major phylogenetic clades, which we have termed alpha-, beta-, gamma-, kappa-, pi-, and sigma-fimbriae. Members of each clade share related operon structures and encode fimbrial subunits with similar protein domains. The proposed classification system offers a simple and convenient method for assigning newly discovered chaperone/usher systems to one of the six major phylogenetic groups.

Functional characterization of the FimH adhesin from Salmonella enterica serovar Enteritidis

Salmonella entericaserovar Enteritidis has emerged during the last 20 years as the major causative agent of food-borne gastroenteritis in humans and as the major infectious agent on poultry farms, replacingSalmonella entericaserovar Typhimurium as the dominant pathogenic serovar. Because adhesion to gut tissues and colonization of the alimentary tract, mediated in large part by the FimH adhesins located on type 1 fimbriae, is an important stage in the pathogenesis of both serovars, the binding properties of the FimH adhesins from these two enteropathogens were compared.SalmonellaEnteritidis FimH protein and theSalmonellaTyphimurium low-adhesive variant of this adhesin were expressed inEscherichia coliand the recombinant proteins were analysed for their ability to bind glycoproteins carrying different oligomannosidic structures and different types of eukaryotic cells. In static binding assays (ELISA and Western blotting) both FimH proteins bound equally well to all three tested glycoproteins (RNase B, horseradish peroxidase and mannan-BSA). In addition, no differences were found in the binding specificity of the FimH proteins and intact cells ofSalmonellaEnteritidis andSalmonellaTyphimurium to human colon carcinoma or bladder cancer cells. The presence of the same amino acid residues at positions 61 (glycine) and 118 (phenylalanine) and the similar binding properties of these two adhesins suggest that the newly described FimH protein ofSalmonellaEnteritidis represents the low-adhesive variant found inSalmonellaTyphimurium. To study the binding specificity ofSalmonellaEnteritidis FimH protein further, direct kinetic analysis using surface plasmon resonance was performed. With this method it was found thatSalmonellaEnteritidis FimH adhesin bound with the highestKdvalue to high-mannose typeN-glycans carried by RNase B; about 100 times lowerKdvalues were obtained in the interactions with mannan-BSA and horseradish peroxidase.