Blocking of fimbria-mediated adherence of Haemophilus influenzae by sialyl gangliosides

Notable Aspects of Glycan-Protein Interactions

This mini review highlights several interesting aspects of glycan-mediated interactions that are common between cells, bacteria, and viruses. Glycans are ubiquitously found on all living cells, and in the extracellular milieu of multicellular organisms. They are known to mediate initial binding and recognition events of both immune cells and pathogens with their target cells or tissues. The host target tissues are hidden under a layer of secreted glycosylated decoy targets. In addition, pathogens can utilize and display host glycans to prevent identification as foreign by the host’s immune system (molecular mimicry). Both the host and pathogens continually evolve. The host evolves to prevent infection and the pathogens evolve to evade host defenses. Many pathogens express both glycan-binding proteins and glycosidases. Interestingly, these proteins are often located at the tip of elongated protrusions in bacteria, or in the leading edge of the cell. Glycan-protein interactions have low affinity and, as a result, multivalent interactions are often required to achieve biologically relevant binding. These enable dynamic forms of adhesion mechanisms, reviewed here, and include rolling (cells), stick and roll (bacteria) or surfacing (viruses).

The Haemophilus influenzae Sap transporter mediates bacterium-epithelial cell homeostasis

Nontypeable Haemophilus influenzae (NTHI) is a commensal inhabitant of the human nasopharynx and a causative agent of otitis media and other diseases of the upper and lower human airway. During colonization within the host, NTHI must acquire essential nutrients and evade immune attack. We previously demonstrated that the NTHI Sap transporter, an inner membrane protein complex, mediates resistance to antimicrobial peptides and is required for heme homeostasis. We hypothesized that Sap transporter functions are critical for NTHI interaction with the host epithelium and establishment of colonization. Thus, we cocultured the parent or the sapA mutant on polarized epithelial cells grown at an air-liquid interface, as a physiological model of NTHI colonization, to determine the contribution of the Sap transporter to bacterium-host cell interactions. Although SapA-deficient NTHI was less adherent to epithelial cells, we observed a significant increase in invasive bacteria compared to the parent strain. Upon internalization, the sapA mutant appeared free in the cytoplasm, whereas the parent strain was primarily found in endosomes, indicating differential subcellular trafficking. Additionally, we observed reduced inflammatory cytokine production by the epithelium in response to the sapA mutant strain compared to the parental strain. Furthermore, chinchilla middle ears challenged with the sapA mutant demonstrated a decrease in disease severity compared to ears challenged with the parental strain. Collectively, our data suggest that NTHI senses host environmental cues via Sap transporter function to mediate interaction with host epithelial cells. Epithelial cell invasion and modulation of host inflammatory cytokine responses may promote NTHI colonization and access to essential nutrients.

Receptor mimicry as novel therapeutic treatment for biothreat agents

The specter of intentional release of pathogenic microbes and their toxins is a real threat. This article reviews the literature on adhesins of biothreat agents, their interactions with oligosaccharides and the potential for anti-adhesion compounds as an alternative to conventional therapeutics. The minimal binding structure of ricin has been well characterised and offers the best candidate for successful anti-adhesion therapy based on the Galβ1-4GlcNAc structure. The botulinum toxin serotypes A-F bind to a low number of gangliosides (GT1b, GQ1b, GD1a and GD1b) hence it should be possible to determine the minimal structure for binding. The minimal disaccharide sequence of GalNAcβ1-4Gal found in the gangliosides asialo-GM1 and asialo-GM2 is required for adhesion for many respiratory pathogens. Although a number of adhesins have been identified in bacterial biothreat agents such as Yersinia pestis, Bacillus anthracis, Francisella tularensis, Brucella species and Burkholderia pseudomallei, specific information regarding their in vivo expression during pneumonic infection is lacking. Limited oligosaccharide inhibition studies indicate the potential of GalNAcβ1-4Gal, GalNAcβ-3Gal and the hydrophobic compound, para-nitrophenol as starting points for the rational design of generic anti-adhesion compounds. A cocktail of multivalent oligosaccharides based on the minimal binding structures of identified adhesins would offer the best candidates for anti-adhesion therapy.

Virulence phenotypes of low-passage clinical isolates of nontypeable Haemophilus influenzae assessed using the chinchilla laniger model of otitis media

Background

The nontypeable Haemophilus influenzae (NTHi) are associated with a spectrum of respiratory mucosal infections including: acute otitis media (AOM); chronic otitis media with effusion (COME); otorrhea; locally invasive diseases such as mastoiditis; as well as a range of systemic disease states, suggesting a wide range of virulence phenotypes. Genomic studies have demonstrated that each clinical strain contains a unique genic distribution from a population-based supragenome, the distributed genome hypothesis. These diverse clinical and genotypic findings suggest that each NTHi strain possesses a unique set of virulence factors that contributes to the course of the disease.

Results

The local and systemic virulence patterns of ten genomically characterized low-passage clinical NTHi strains (PittAA – PittJJ) obtained from children with COME or otorrhea were stratified using the chinchilla model of otitis media (OM). Each isolate was used to bilaterally inoculate six animals and thereafter clinical assessments were carried out daily for 8 days by blinded observers. There was no statistical difference in the time it took for any of the 10 NTHi strains to induce otologic (local) disease with respect to any or all of the other strains, however the differences in time to maximal local disease and the severity of local disease were both significant between the strains. Parameters of systemic disease indicated that the strains were not all equivalent: time to development of the systemic disease, maximal systemic scores and mortality were all statistically different among the strains. PittGG induced 100% mortality while PittBB, PittCC, and PittEE produced no mortality. Overall Pitt GG, PittII, and Pitt FF produced the most rapid and most severe local and systemic disease. A post hoc determination of the clinical origins of the 10 NTHi strains revealed that these three strains were of otorrheic origin, whereas the other 7 were from patients with COME.

Conclusion

Collectively these data suggest that the chinchilla OM model is useful for discriminating between otorrheic and COME NTHi strains as to their disease-producing potential in humans, and combined with whole genome analyses, point the way towards identifying classes of virulence genes.

Sialidase fusion protein as a novel broad-spectrum inhibitor of influenza virus infection

Influenza is a highly infectious disease characterized by recurrent annual epidemics and unpredictable major worldwide pandemics. Rapid spread of the highly pathogenic avian H5N1 strain and escalating human infections by the virus have set off the alarm for a global pandemic. To provide an urgently needed alternative treatment modality for influenza, we have generated a recombinant fusion protein composed of a sialidase catalytic domain derived from Actinomyces viscosus fused with a cell surface-anchoring sequence. The sialidase fusion protein is to be applied topically as an inhalant to remove the influenza viral receptors, sialic acids, from the airway epithelium. We demonstrate that a sialidase fusion construct, DAS181, effectively cleaves sialic acid receptors used by both human and avian influenza viruses. The treatment provides long-lasting effect and is nontoxic to the cells. DAS181 demonstrated potent antiviral and cell protective efficacies against a panel of laboratory strains and clinical isolates of IFV A and IFV B, with virus replication inhibition 50% effective concentrations in the range of 0.04 to 0.9 nM. Mouse and ferret studies confirmed significant in vivo efficacy of the sialidase fusion in both prophylactic and treatment modes.

Bacterial-associated cholera toxin and GM1 binding are required for transcytosis of classical biotype Vibrio cholerae through an in vitro M cell model system

To elucidate mechanisms involved in M cell uptake and transcytosis of Vibrio cholerae, we used an in vitro model of human M-like cells in a Caco-2 monolayer. Interspersed among the epithelial monolayer of Caco-2 cells we detect cells that display M-like features with or without prior lymphocyte treatment and we have established key parameters for V. cholerae transcytosis in this model. Cholera toxin (CT) mutants lacking the A subunit alone or both the A and B subunits were deficient for transcytosis. We explored this finding further and showed that expression of both subunits is required for binding by whole V. cholerae to immobilized CT receptor, the glycosphingolipid GM1. Confocal microscopy showed CT associated with transcytosing bacteria, and transcytosis was inhibited by pre-incubation with GM1 before infection. Finally, heat treatment of the bacterial cells caused a loss of binding to GM1 that was correlated with a significant decrease in uptake and transcytosis by the monolayer. Our data support a model in which the ability of bacteria to interact with GM1 in a CT-dependent fashion plays a critical role in transcytosis of V. cholerae by M cells.

NontypeableHaemophilus influenzae-binding gangliosides of human respiratory (HEp-2) cells have a requisite lacto/neolacto core structure

Nontypeable Haemophilus influenzae (NTHI) are a major cause of human infections. We previously demonstrated high affinity and high specificity binding of NTHI to minor gangliosides of human respiratory (HEp-2) cells and macrophages, but not to brain gangliosides. We further identified the NTHI-binding ganglioside of human macrophages as alpha2,3-sialylosylparagloboside (IV3NeuAc-nLcOse4Cer, nLM1), which possesses a neolacto core structure that is absent in brain gangliosides. This supported a hypothesis that lacto/neolacto core carbohydrates are critical for NTHI-ganglioside binding. To investigate, we determined the core carbohydrate structure of NTHI-binding gangliosides of HEp-2 cells, through multiple approaches, including specific enzymatic degradation, mass spectral analysis and gas-liquid chromatography. Our analyses denote the following critical structural attributes of NTHI-binding gangliosides: (1) a conserved lacto/neolacto core structure; (2) requisite sialylation, which may be either internal or external, with alpha2,3 (human macrophages) or alpha2,6 (HEp-2 cells) anomeric linkages; (3) internalized galactose residues. Mass spectral and gas chromatographic analyses confirm that NTHI-binding gangliosides of HEp-2 cells possess lacto/neolacto carbohydrate cores and identify the structure of the major peak as NeuAcalpha2-6Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-1Cer (alpha2,6-sialosylparagloboside, nLM1). Collectively, our studies denote NTHI-binding gangliosides as lacto/neolacto series structures.

A recombinant P4 protein of Haemophilus influenzae induces specific immune responses biologically active against nasopharyngeal colonization in mice after intranasal immunization

Outer membrane protein P4, together with P6, is highly conserved among all typeable and nontypeable strains of Haemophilus influenzae (H. influenzae). Thus, the protein is an attractive antigen for the inclusion in a vaccine against nontypeable H. influenzae (NTHi). However, the ability of P4 to induce antibodies protective against NTHi infections is still controversial. In this study, we investigated the specific mucosal immune responses against NTHi induced by intranasal immunization with the lipidated form of recombinant P4 protein (rP4) and non-fatty acylated recombinant P6 protein (rP6) with or without cholera toxin (CT) in BALB/c mice model. Intranasal immunization with either rP4+CT, a mixture of rP4 and rP6+CT, or rP4 and rP6 without CT elicited anti-rP4 specific IgG antibody in serum of mice. Intranasal immunization with either rP4+CT or a mixture of rP4, rP6+CT elicited anti-rP4 specific IgA antibody in nasopharyngeal washing (NPW), while intranasal immunization with rP4 and rP6 without CT did not induced anti-rP4 specific IgA antibody responses in NPWs. Sera from mice intranasally immunized with rP4+CT and a mixture of rP4, rP6+CT also showed bactericidal activity. Significant clearance of NTHi in nasopharynx was seen 3 days after the inoculation of live NTHi in mice intranasally immunized with rP4+CT. The current findings suggested that P4 would be a useful antigen as the component of the vaccine to induce protective immune responses against NTHi. The use of an intranasal vaccine composed of the different surface protein antigens is an attractive strategy for the development of a vaccine against NTHi.

Common oligosaccharide moieties inhibit the adherence of typical and atypical respiratory pathogens

Intervention in bacterial adhesion to host cells is a novel method of overcoming current problems associated with antibiotic resistance. Antibiotic-resistant strains of bacteria that cause respiratory tract infections are a problem in hospitals and could be used in bioterrorist attacks. A range of bacterial species was demonstrated to attach to an alveolar epithelial (A549) cell line. In all cases, cell surface oligosaccharides were important in attachment, demonstrated by reduced adhesion when A549 cells were pre-treated with tunicamycin. Bacillus anthracis and Yersinia pestis displayed a restricted tropism for oligosaccharides compared to the environmental, opportunistic pathogens, Pseudomonas aeruginosa, Burkholderia cenocepacia, Burkholderia pseudomallei and Legionella pneumophila. The compound with the greatest anti-adhesion activity was p-nitrophenol. Other generic attachment inhibitors included the polymeric saccharides (dextran and heparin), GalNAcbeta1-4Gal, GalNAcbeta1-3Gal, Galbeta1-4GlcNAc and Galbeta1-3GlcNAc. Burkholderia pseudomallei attachment was particularly susceptible to oligosaccharide inhibition. Combinations of such compounds may serve as a novel generic therapeutics for respiratory tract infections.

Prevalence of the hifBC, hmw1A, hmw2A, hmwC, and hia Genes in Haemophilus influenzae Isolates

Adherence of Haemophilus influenzae to respiratory epithelial cells is the first step in the pathogenesis of H. influenzae infection and is facilitated by the action of several adhesins located on the surface of the bacteria. In this study, prevalences of hifBC, which represent the pilus gene cluster; hmw1A, hmw2A, and hmwC, which represent high-molecular-weight (HMW) adhesin genes; and hia, which represents H. influenzae adhesin (Hia) genes were determined among clinical isolates of encapsulated type b (Hib) and nonencapsulated (NTHi) H. influenzae. hifBC genes were detected in 109 of 170 (64%) Hib strains and in 46 of 162 (28%) NTHi isolates (P = 0.0001) and were more prevalent among the invasive type b strains than invasive NTHi strains (P = 0.00003). Furthermore, hifBC genes were significantly more prevalent (P = 0.0398) among NTHi throat isolates than NTHi middle ear isolates. hmw1A, hmw2A, hmwC, and hia genes were not detected in Hib strains. Among NTHi isolates, the prevalence of hmw1A was 51%, the prevalence of hmw2A was 23%, the prevalence of hmwC was 48%, and the prevalence of hia was 33%. The hmw genes were significantly more prevalent among middle ear than throat isolates, while hia did not segregate with a respiratory tract site. These results show the variability of the presence of adhesin genes among clinical H. influenzae isolates and suggest that hemagglutinating pili may play a larger role in H. influenzae nasopharyngeal colonization than in acute otitis media whereas the HMW adhesins may be virulence factors for acute otitis media.

Prevalence and distribution of adhesins in invasive non-type b encapsulated Haemophilus influenzae

Adhesion to the respiratory epithelium plays an important role in Haemophilus influenzae infection. The distribution of H. influenzae adhesins in type b and nontypeable strains has been characterized, but little is known about the prevalence of these factors in non-type b encapsulated strains. We analyzed 53 invasive type a, type e, and type f strains for the presence of hap, hia, hmw, and hif genes; Hap, Hia, and HMW1/2 adhesins; and hemagglutinating pili. The hap gene was ubiquitous, and homologs of hmw and hia were present in 7 of 53 (13.2%) and 45 of 53 (84.9%) strains, respectively. Hap was detected in 28 of 45 (62.2%) hap(+) strains, HMW1/2 was detected in 5 of 7 (71.4%) hmw(+) strains, and Hia was detected in 31 of 45 (68.8%) hia(+) strains. The hif gene cluster was present in 26 of 53 strains (49.1%), and 21 of 26 hif(+) strains (80.8%) agglutinated (HA) red blood cells. Nine isolates exhibited HA but lacked the hif gene cluster. The distribution of adhesin genes correlated with the genetic relatedness of the strains. Strains belonging to one type a clonotype and the major type e clonotype possessed hia but lacked the hif cluster. Strains belonging to the second type a clonotype possessed both hia and hif genes. All type f strains belonging to the major type f clonotype possessed hia and lacked hifB. Although the specific complement of adhesin genes in non-type b encapsulated H. influenzae varies, most invasive strains express Hap and Hia, suggesting these adhesins may be especially important to the virulence of these organisms.

Molecular and cellular determinants of non-typeable Haemophilus influenzae adherence and invasion

Non-typeable Haemophilus influenzae is a common cause of human disease and initiates infection by colonizing the upper respiratory tract. Based on information from histopathologic specimens and in vitro studies with human cells and tissues in culture, non-typeable H. influenzae is capable of efficient adherence and appreciable invasion, properties that facilitate the process of colonization. A number of adhesive factors exist, each recognizing a distinct host cell structure and influencing cellular binding specificity. In addition, at least three invasion pathways exist, including one resembling macropinocytosis, a second mediated via the PAF receptor and a third involving beta-glucan receptors. Organisms are also capable of disrupting cell-cell junctions and passing between cells to the subepithelial space.

Analysis of pilus adhesins from Haemophilus influenzae biotype IV strains

A subset of nontypeable Haemophilus influenzae (NTHI) biotype IV isolates from the human genital tract or from infected newborn infants forms a cryptic genospecies characterized by, among other features, the presence of peritrichous pili. The objective of this study was to determine the similarity of these pili to hemagglutinating, HifA- and HifE-containing pili expressed by respiratory H. influenzae isolates. For this analysis, the presence of hifA and hifE and their gene products in NTHI biotype IV strains was assessed, the binding of H. influenzae biotype IV strains to human epithelial cells was characterized, possible genital tissue tropism of these isolates was explored, and the role of HifA- and HifE-possessing pili in the adhesion of NTHI biotype IV strains to human epithelial cells was determined. None of the six biotype IV NTHI isolates tested agglutinated human red blood cells, nor could they be enriched for hemagglutinating variants. Although hifA, which encodes the major structural subunit of hemagglutinating pili, and hifE, which encodes the tip adhesin of hemagglutinating pili, were detected by PCR from six and five, respectively, of the six biotype IV strains tested, neither HifA nor HifE (the gene products of hifA and hifE) were detected in any of these strains by Western blot analysis using antisera that recognize HifA and HifE of respiratory strains. Transmission electron microscopy showed no surface pili on the two biotype IV H. influenzae isolates examined; strain 4162 containing an insertional mutation in hifA also showed no surface pili, whereas strain 1595 containing an insertional mutation in hifB showed pilus-like structures that were shorter and thicker than hemagglutinating pili of the respiratory strains AAr176 and M43. In enzyme-linked immunosorbent assays, biotype IV strains adhered to 16HBE14o(-) and HEp-2 cells of respiratory origin as well as to ME180 and HeLa cells of genital origin. This adherence was not pilus specific, however, as GM-1, a known pilus receptor analog, did not inhibit binding of biotype IV strains to ME180, HEp-2, or HeLa cells, and GM-1 inhibition of binding to 16HBE14o(-) cells did not correlate with the presence of hifE. While both nonpiliated variants and hifA and hifB (encoding the pilus chaperone) mutants of respiratory strain AAr176 showed reduced binding (64 to 87% of that of piliated AAr176) to 16HBE14o(-) and ME180 cells, hifA and hifB mutants of the biotype IV strains showed minimal reduction in binding to these cell lines (91 to 98% of that of wild-type strains). Thus, although biotype IV H. influenzae isolates of the cryptic genospecies possess the genes that code for HifA- and HifE-containing hemagglutinating pili, epithelial cell adherence exhibited by these strains is not mediated by expression of hemagglutinating pili.

The variable P5 proteins of typeable and non-typeable Haemophilus influenzae target human CEACAM1

Haemophilus influenzae, a commensal of the human respiratory mucosa, is an important cause of localized and systemic infections. We have recently shown that numerous strains of capsulate (typeable) and acapsulate (non-typeable) H. influenzae target the carcinoembryonic antigen (CEA) family of cell adhesion molecules (CEACAMs). Moreover, the ligands appeared to be antigenically variable and, when using viable typeable bacteria, their adhesive functions were inhibited by the presence of capsule. In this report, we show that the antigenically variable outer membrane protein, P5, expressed by typeable and non-typeable H. influenzae targets human CEACAM1. Variants and mutants lacking the expression of P5 of all strains tested were unable to target purified soluble receptors. A non-typeable strain that did not interact with CEACAM1 was made adherent to both the soluble receptors and CEACAM1-transfected Chinese hamster ovary cells by transformation with the P5 gene derived from the adherent typeable strain Rd. However, several H. influenzae mutants lacking P5 expression continued to bind the cell-bound CEACAM1 receptors. These observations suggest that (i) CEACAM1 alone can support P5 interactions and (ii) some strains contain additional ligands with the property to target CEACAM1 but require the receptor in the cellular context. The identification of a common ligand in diverse strains of H. influenzae and the presence of multiple ligands for the same receptor suggests that targeting of members of the CEACAM family of receptors may be of primary significance in colonization and pathogenesis of H. influenzae strains.

The pathogenesis of nontypable Haemophilus influenzae otitis media

Nontypable Haemophilus influenzae is a common cause of otitis media and initiates infection by colonizing the upper respiratory tract. In this article, I review our current understanding of the molecular determinants of H. influenzae colonization and discuss the relationship between colonization and otitis media.

Characterization of non-type B Haemophilus influenzae strains isolated from patients with invasive disease. The HI Study Group

Forty-one non-type b Haemophilus influenzae isolates from cases of invasive disease were characterized. By PCR capsular genotyping, 33 nonencapsulated strains, 4 type f isolates, and 4 b(-) strains were identified. By pulsed-field gel electrophoresis, the nonencapsulated isolates exhibited great genetic heterogenicity, whereas the type f and the b(-) strains seemed to have a clonal spread. Occurrence of the hifA gene was found by PCR in 18% of the nonencapsulated, 50% of the b(-), and all of the type f strains. Hemagglutinating fimbriae were generally expressed by nonencapsulated isolates when fimbrial gene hifA was present. Two nonencapsulated isolates not susceptible to ampicillin were detected; no strains were positive for beta-lactamase production.

Interaction of fimbriae of Haemophilus influenzae type B with heparin-binding extracellular matrix proteins

The interaction of the fimbriae of Haemophilus influenzae type b (Hib) with two heparin-binding extracellular matrix proteins, human fibronectin (Fn) and heparin-binding growth-associated molecule (HB-GAM) from mouse, were studied. The fimbriated Hib strain 770235 fim+, as well as the recombinant strain E. coli HB101(pMH140), which expressed Hib fimbriae, adhered strongly to Fn and HB-GAM immobilized on glass. Purified Hib fimbriae bound to Fn and HB-GAM, and within the Fn molecule, the binding was localized to the N-terminal 30,000-molecular-weight (30K) and 40K fragments, which contain heparin-binding domains I and II, respectively. Fimbrial binding to Fn, HB-GAM, and the 30K and the 40K fragments was inhibited by high concentrations of heparin. The results show that fimbriae of Hib interact with heparin-binding extracellular matrix proteins. The nonfimbriated Hib strain 770235 fim- exhibited a low level of adherence to Fn but did not react with HB-GAM, indicating that Hib strains also possess a fimbria-independent mechanism to interact with Fn.

Pilus-mediated adherence of Haemophilus influenzae to human respiratory mucins

Haemophilus influenzae, especially the nontypeable strains, are among the most common pathogens encountered in patients with chronic lung disease and otitis media. We and others have demonstrated that respiratory isolates of nontypeable H. influenzae bind to human mucins, but the mechanism of binding is not entirely clear. We have therefore examined the role of pili in the adherence of both type b and nontypeable H. influenzae to human respiratory mucins. We used isogenic H. influenzae strains with a mutation in the structural gene for pilin (hifA), a laboratory H. influenzae strain transformed with a type b pilus gene cluster (from strain C54), antibodies raised against H. influenzae HifA, and Escherichia coli strains carrying a cloned type b pilus gene cluster (from strain AM30) in these studies. All bacteria lacking HifA or the pilus gene cluster had decreased adherence of piliated H. influenzae to mucins, and Fab fragments of anti-HifA antibodies inhibited the adherence. E. coli strains carrying the cloned type b pilus gene cluster were six to seven times more adhesive than strains carrying the vector. The role of other putative adhesins was not examined and thus cannot be excluded, but these studies support a role for pili in the binding of H. influenzae to human respiratory mucins.

Haemophilus influenzae stimulates ICAM-1 expression on respiratory epithelial cells

Epithelial cells interact directly with bacteria in the environment and play a critical role in airway defense against microbial pathogens. In this study, we examined the response of respiratory epithelial cells to infection with nontypable Haemophilus influenzae. Using an in vitro cell culture model, we found that epithelial cell monolayers released significant quantities of IL-8 and expressed increased levels of ICAM-1 mRNA and surface protein in response to H. influenzae. In contrast, levels of IL-1beta, TNF-alpha, and MHC class I were not significantly affected, suggesting preferential activation of a specific subset of epithelial genes directed toward defense against bacteria. Induction of ICAM-1 required direct bacterial interaction with the epithelial cell surface and was not reproduced by purified H. influenzae lipooligosaccharide. Consistent with a functional role for this response, induction of ICAM-1 by H. influenzae mediated increased neutrophil adherence to the epithelial cell surface. Furthermore, in an in vivo murine model of airway infection with H. influenzae, increased epithelial cell ICAM-1 expression coincided with increased chemokine levels and neutrophil recruitment in the airway. These results indicate that ICAM-1 expression on human respiratory epithelial cells is induced by epithelial cell interaction with H. influenzae and suggest that an ICAM-1-dependent mechanism can mediate neutrophil adherence to these cells independent of inflammatory mediator release by other cell types. Direct induction of specific epithelial cell genes (such as ICAM-1 and IL-8) by bacterial infection may allow for rapid and efficient innate defense in the airway.

Evidence for donor strand complementation in the biogenesis of Haemophilus influenzae haemagglutinating pili

Haemophilus influenzae haemagglutinating pili are surface appendages that promote attachment to host cells and facilitate respiratory tract colonization, an essential step in the pathogenesis of disease. In contrast to other well-characterized forms of pili, H. influenzae haemagglutinating pili are two-stranded helical structures. Nevertheless, haemagglutinating pili are assembled by a pathway that involves a periplasmic chaperone and an outer membrane usher, analogous to the prototype pathway involved in the biogenesis of Escherichia coli P pili. In this study, we performed site-directed mutagenesis of the H. influenzae HifB chaperone and HifA major pilus subunit at positions homologous to sites important for chaperone-subunit interactions and subunit oligomerization in P pili. Mutations at putative subunit binding pocket residues in HifB or at the penultimate tyrosine in HifA abolished formation of HifB-HifA periplasmic complexes, whereas mutations at the -14 glycine in HifA had no effect on HifB-HifA interactions but abrogated HifA oligomerization. To define further the constraints of the interaction between HifA and HifB, we examined the interchangeability of pilus gene cluster components from H. influenzae type b strain Eagan (hifA-hifEEag) and the related H. influenzae biogroup aegyptius strain F3031 (hifA-hifEF3031). Functional pili were assembled both with HifAEag and the strain F3031 gene cluster and with HifAF3031 and the strain Eagan gene cluster, underscoring the flexibility of the H. influenzae chaperone/usher pathway in incorporating HifA subunits with significant sequence diversity. To gain additional insight into the interactive surfaces of HifA and HifB, we aligned HifA sequences from 20 different strains and then modelled the HifA structure based on the recently crystallized PapD-PapK complex. Analysis of the resulting structure revealed high levels of sequence conservation in regions predicted to interact with HifB, and maximal sequence diversity in regions potentially exposed on the surface of assembled pili. These results suggest broad applicability of structure-function relationships identified in studies of P pili, including the concepts of donor strand complementation and donor strand exchange. In addition, they provide insight into the structure of HifA and suggest a basis for antigenic variation in H. influenzae haemagglutinating pili.

Molecular determinants of the pathogenesis of disease due to non-typable Haemophilus influenzae

Non-typable Haemophilus influenzae is a common commensal organism in the human upper respiratory tract and an important cause of localized respiratory tract disease. The pathogenesis of disease begins with bacterial colonization of the nasopharynx, a process that involves establishment on the mucosal surface and evasion of local immune mechanisms. Under the proper circumstances, the organism spreads contiguously to the middle ear, the sinuses, or the lungs, and then stimulates a brisk inflammatory response, producing symptomatic infection. In this review, we summarize our present understanding of the molecular determinants of this sequence of events. Continued investigation of the molecular mechanism of non-typable H. influenzae pathogenicity should facilitate development of novel approaches to the treatment and prevention of H. influenzae disease.

Adhesin expression in matched nasopharyngeal and middle ear isolates of nontypeable Haemophilus influenzae from children with acute otitis media

The HMW1 and HMW2 proteins, Hia, and hemagglutinating pili are important adherence factors in nontypeable Haemophilus influenzae. To gain insight into the relative importance of these adhesins in nasopharyngeal colonization and localized respiratory tract disease, we assessed their expression in matched nasopharyngeal and middle ear isolates of nontypeable H. influenzae from 17 children with acute otitis media. In all patients, including 11 with bilateral disease, the matched isolates were isogenic based on total protein profiles and genomic fingerprints. Of the nasopharyngeal isolates, 14 expressed only HMW1/HMW2-like proteins, 1 expressed only Hia, 1 expressed only pili, and 1 expressed both Hia and pili. Further analysis revealed concordance between nasopharyngeal isolates and the matched middle ear isolates for expression of the HMW1/HMW2-like proteins and Hia. In contrast, in the two children whose nasopharynges were colonized by piliated organisms, the corresponding middle ear isolates were nonpiliated and could not be enriched for piliation. Nevertheless, Southern analysis revealed that these two middle ear isolates contained all five hif genes required for pilus biogenesis and had no evidence of major genetic rearrangement. In summary, the vast majority of isolates of nontypeable H. influenzae associated with acute otitis media express HMW1/HMW2-like proteins, with expression present in both the nasopharynx and the middle ear. A smaller fraction of nasopharyngeal isolates express pili, while isogenic strains recovered from the middle ear are often refractory to enrichment for piliation. We speculate that the HMW adhesins and Hia are important at multiple steps in the pathogenesis of otitis media while pili contribute to early colonization and then become dispensable.

Attachment of nontypable Haemophilus influenzae to human pharyngeal epithelial cells mediated by a ganglioside receptor

Nontypable Haemophilus influenzae (NTHI) is one of the major pathogens of human respiratory infections and has the ability to attach to pharyngeal epithelial cells. We characterized the epithelial cell receptor to which NTHI bind. Neuraminidase pretreatment of pharyngeal epithelial cells resulted in a significant decrease in NTHI attachment, suggesting sialic acid as an important component of the receptor. The attachment was not decreased in NTHI pretreated with 1,000 microg/ml of fucose, N-acetyl-neuraminic acid, N-acetyl-glucosamine, N-acetyl-galactosamine, acetyl-salicylic acid and colominic acid. Only treatment with gangliosides D1a, D1b and D2 at a concentration of 12.5 microg/ml significantly decreased the attachment. On the other hand, treatment with gangliosides M1, M2, M3, D3, T1b and asialoganglioside M1 did not decrease the attachment of NTHI. Only ganglioside D2 inhibited the attachment significantly at a concentration of 12.5 ng/ml. Other isolates of NTHI showed a decrease in attachment after treatment with ganglioside D2. Treatment of cells with anti-human GD2 monoclonal antibody also decreased the attachment of NTHI in a dose-dependent manner. This study indicates that sialic acid glycoconjugate, GD2, is one of the receptors of NTHI on human pharyngeal epithelial cells.

Immunologic and structural relationships of the minor pilus subunits among Haemophilus influenzae isolates

Two proteins, HifD and HifE, have been identified as structural components of Haemophilus influenzae pili. Both are localized at the pilus tip, and HifE appears to mediate pilus adherence to host cells. In this study we examined the immunologic and structural diversity of these pilus subunits among type b H. influenzae (Hib) and nontypeable H. influenzae (NTHI) strains. Western immunoblot analysis revealed that antibodies directed against the C terminus of HifD and HifE from Hib strain Eagan bound to HifD and HifE proteins, respectively, of all piliated Hib and NTHI strains tested. Whole-cell enzyme-linked immunosorbent assays showed that antibodies specific for native HifD or HifE of strain Eagan also bound to all piliated Hib strains but did not bind to the piliated NTHI strains. Antibodies against HifE of strain Eagan inhibited the binding of Hib to human erythrocytes but did not inhibit the binding of NTHI strains. Restriction fragment length polymorphism (RFLP) analysis was used to determine strain-to-strain structural differences within hifD and hifE genes, either by PCR or by nucleotide sequence analysis. DNA and derived amino acid sequence analyses of HifD and HifE confirmed the uniqueness of the RFLP types. The hifD and hifE genes of all type b strains showed identical restriction patterns. Analysis of hifD and hifE genes from the NTHI strains, however, revealed seven unique RFLP patterns, suggesting that these genes encode proteins with diverse primary structures. These results indicate that HifD and HifE are immunologically and structurally similar among the Hib strains but vary among the NTHI strains.

Nontypeable Haemophilus influenzae: pathogenesis and prevention

In this paper, we describe the ability of nontypeable Haemophilus influenzae (NTHi) to coexist with the human host and the devastating results associated with disruption of the delicate state of balanced pathogenesis, resulting in both acute and chronic respiratory tract infections. It has been seen that the strains of NTHi causing disease show a marked genetic and phenotypic diversity but that changes in the lipooligosaccharide (LOS) and protein size and antigenicity in chronically infected individuals indicate that individual strains of NTHi can remain and adapt themselves to avoid expulsion from their infective niche. The lack of reliance of NTHi on a single mechanism of attachment and its ability to interact with the host with rapid responses to its environment confirmed the success of this organism as both a colonizer and a pathogen. In vitro experiments on cell and organ cultures, combined with otitis media and pulmonary models in chinchillas, rats, and mice, have allowed investigations into individual interactions between NTHi and the mammalian host. The host-organism interaction appears to be a two-way process, with NTHi using cell surface structures to directly interact with the mammalian host and using secreted proteins and LOS to change the mammalian host in order to pave the way for colonization and invasion. Many experiments have also noted that immune system evasion through antigenic variation, secretion of enzymes and epithelial cell invasion allowed NTHi to survive for longer periods despite a specific immune response being mounted to infection. Several outer membrane proteins and LOS derivatives are discussed in relation to their efficacy in preventing pulmonary infections and otitis media in animals. General host responses with respect to age, genetic makeup, and vaccine delivery routes are considered, and a mucosal vaccine strategy is suggested.

The fimbria gene cluster of nonencapsulated Haemophilus influenzae

The occurrence of fimbria gene clusters in nonencapsulated Haemophilus influenzae strains from chronic bronchitis patients (n = 58), patients with acute otitis media (n = 13), and healthy carriers (n = 12) was determined by DNA hybridization and PCR, based on sequences of fimbriate H. influenzae type b. Although an average of 18% of all nonencapsulated strains had a fimbria gene cluster consisting of hifA to hifE inserted in the chromosome between purE and pepN, differences in the frequency of fimbria cluster-positive strains were observed, depending on the source of isolates. The compositions of the fimbria gene clusters of seven strains from chronic bronchitis patients and one strain from an otitis media patient were analyzed in more detail. After enrichment for fimbria expression, the promoter of the gene cluster contained 10 TA repeats (n = 2), leading to optimal positioning between the -10 and -35 promoter regions. The promoter regions of five fimbria-negative strains were sequenced; four were found to have nine TA repeats, and one had only four TA repeats. The protein sequence of three ganglioside GM1-specific HifA adhesins consisted of conserved regions intermingled with regions of sequence diversity. hifA appeared to be flanked by intergenic regions that varied between strains and contained both direct and inverted DNA repeats. Since noncoding DNA between hifA and purE has not been found in H. influenzae type b, these DNA sequences are probably not essential for fimbria expression. An analysis of strains lacking the gene cluster revealed the presence of similar sequences in 13 of 15 strains from chronic bronchitis patients, 5 of 5 strains from otitis media patients, and 3 of 5 strains from healthy carriers. The lengths of these intergenic regions were the same for multiple isolates of strains obtained during persistent infections. The presence or absence and the composition of the fimbria gene cluster and other sequences between the flanking genes purE and pepN suggest that the fimbria gene cluster was originally contained on a mobile element.

Specific binding of Haemophilus influenzae to minor gangliosides of human respiratory epithelial cells

Gangliosides are sialylated glycosphingolipids that serve as receptors for various bacteria. To investigate endogenous gangliosides of human respiratory epithelial cells as potential receptors for Haemophilus influenzae, three strains, including nontypeable H. influenzae (NTHI) 1479, and isogenic fimbriated (f+) and nonfimbriated (f0) H. influenzae type b 770235, were 3H labeled and overlaid on two-dimensional thin-layer chromatography (TLC) plates containing either purified HEp-2 gangliosides or murine brain gangliosides. NTHI 1479 bound exclusively to two distinct minor ganglioside doublets, with mobilities near that of GM1. These minor gangliosides comprised only 14.2 and 9.4% of the total, respectively. NTHI 1479 also bound to a distinct ganglioside of human macrophages whose chromatographic mobilities closely resemble those of one of the NTHI-binding gangliosides of HEp-2 cells. H. influenzae type b 770235 f+ and f0 each bound to a different minor HEp-2 ganglioside doublet, with proportionately weaker affinity for a major ganglioside doublet. Remarkably, none of the three strains bound to any murine brain gangliosides. Moreover, when 80 to 90% of sialic acid residues were enzymatically removed from HEp-2 gangliosides, NTHI 1479 binding was proportionately impaired, compared with untreated controls. Our findings support a role for specific gangliosides of specific cells as receptors for H. influenzae strains. Our findings further demonstrate that individual minor gangliosides possess unique biological properties.

Brief heat shock treatment induces a long-lasting alteration in the glycolipid receptor binding specificity and growth rate of Haemophilus influenzae

After brief heat shock treatment, clinical strains of nontypeable Haemophilus influenzae show a long-lasting change in the binding specificity for glycolipids and a markedly increased growth rate in vitro. Non-heat-shocked H. influenzae specifically binds to phosphatidylethanolamine (PE), gangliotetraosylceramide (Gg4), and gangliotriosylceramide (Gg3) and binds minimally to sulfatoxygalactosylceramide (SGC; also called sulfatide). After a 5-min heat shock at 42 degrees C, strains of H. influenzae showed a marked increase in binding to SGC and acquired the ability to bind to sulfatoxygalactosylglycerol (SGG) in thin-layer chromatography overlays. Additionally, heat-shocked H. influenzae cells showed an increased growth rate (twofold). Increased sulfatide binding and growth rate were retained for approximately 60 generations, after which the heat-shocked organisms reverted to their original glycolipid binding pattern (i.e., PE, Gg3, and Gg4) and growth rate. Such organisms could then be reexposed to heat, and the heat shock phenotype would be reestablished. After exposure of the organisms to brief heat shock, Western blotting of a surface extract of H. influenzae with anti-bovine-brain hsp-70 monoclonal antibody showed an increase in two protein bands at 82 and 60 kDa. This antibody was a potent inhibitor of the binding of heat-shocked H. influenzae to SGC and SGG but had no effect on PE, Gg3, or Gg4 binding in vitro. In contrast, an antibody against an H. influenzae PE-Gg3-Gg4-binding adhesin that was recently identified (J. Busse, E. Hartmann, and C. A. Lingwood, J. Infect. Dis. 175:77-83, 1996) selectively inhibited the organism's binding to PE and Gg3. This indicates that cell surface hsp-70-related heat shock proteins can mediate H. influenzae attachment to sulfoglycolipids following heat shock. We suggest that such increased binding to sulfated glycolipids may be a response to fever following H. influenzae infection in humans.

Sialic acids in molecular and cellular interactions

Sialic acids (Sias) are terminal components of many glycoproteins and glycolipids especially of higher animals. In this exposed position they contribute significantly to the structural properties of these molecules, both in solution and on cell surfaces. Therefore, it is not surprising that Sias are important regulators of cellular and molecular interactions, in which they play a dual role. They can either mask recognition sites or serve as recognition determinants. Whereas the role of Sias in masking and in binding of pathogens to host cells has been documented over many years, their role in nonpathological cellular interaction has only been shown recently. The aim of this chapter is to summarize our knowledge about Sias in masking, for example, galactose residues, and to review the progress made during the past few years with respect to Sias as recognition determinants in the adhesion of pathogenic viruses, bacteria, and protozoa, and particularly as binding sites for endogenous cellular interaction molecules. Finally, perspectives for future research on these topics are discussed.

DNA repeats identify novel virulence genes in Haemophilus influenzae

The whole genome sequence (1.83 Mbp) of Haemophilus influenzae strain Rd was searched to identify tandem oligonucleotide repeat sequences. Loss or gain of one or more nucleotide repeats through a recombination-independent slippage mechanism is known to mediate phase variation of surface molecules of pathogenic bacteria, including H. influenzae. This facilitates evasion of host defenses and adaptation to the varying microenvironments of the host. We reasoned that iterative nucleotides could identify novel genes relevant to microbe-host interactions. Our search of the Rd genome sequence identified 9 novel loci with multiple (range 6-36, mean 22) tandem tetranucleotide repeats. All were found to be located within putative open reading frames and included homologues of hemoglobin-binding proteins of Neisseria, a glycosyltransferase (lgtC gene product) of Neisseria, and an adhesin of Yersinia. These tetranucleotide repeat sequences were also shown to be present in two other epidemiologically different H. influenzae type b strains, although the number and distribution of repeats was different. Further characterization of the lgtC gene showed that it was involved in phenotypic switching of a lipopolysaccharide epitope and that this variable expression was associated with changes in the number of tetranucleotide repeats. Mutation of lgtC resulted in attenuated virulence of H. influenzae in an infant rat model of invasive infection. These data indicate the rapidity, economy, and completeness with which whole genome sequences can be used to investigate the biology of pathogenic bacteria.

Molecular determinants of the interaction between Haemophilus influenzae and human cells

Haemophilus influenzae is a human-specific pathogen that must colonize the human upper respiratory tract to avoid extinction. On occasion, organisms penetrate the epithelial barrier and cause bacteremic disease or spread within the respiratory tract to produce localized disease. Attachment to host epithelium is fundamental to the process of colonization and to the pathogenesis of disease. Accordingly, H. influenzae has evolved to express a number of factors that promote interaction with human epithelial cells. Our current understanding of H. influenzae type b and nontypable H. influenzae adhesins is reviewed in this report. In addition, models are proposed for the interrelationship of these molecules.

Adherence of nontypeable Haemophilus influenzae to respiratory epithelium of otitis-prone and normal children

Three hundred six children were enrolled at birth in a prospective study of otitis media and followed up for 2 years. Adherence of nontypeable Haemophilus influenzae to buccal epithelial cells was compared between otitis-prone children and age- and sex-matched normal controls at birth, 1 year, and 2 years. The mean +/- SD/median percent adherence was similar for the two groups at birth (1.6 +/- 2.3/1.0 versus 1.2 +/- 1.4/1.0; NS) and at 2 years (1.6 +/- 1.7/1.5 versus 2.1 +/- 2.1/1.5; NS). At 1 year of age the adherence rate for the otitis-prone group (2.4 +/- 2.6/1.0) was statistically greater than that for the control group (1.0 +/- 1.3/0.0; p < .02). Because this difference is probably clinically insignificant, other explanations must be sought for the increased colonization rates of nontypeable H influenzae observed in otitis-prone children.

Antibodies to Haemophilus influenzae type b polysaccharide affect bacterial adherence and multiplication

Since immunization of infants with conjugated Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) vaccines results in a reduction of colonization, we determined the inhibitory effect of anti-Hib PS on two steps in the colonization, i.e., adherence of H. influenzae to nasopharyngeal epithelium and bacterial growth. Monoclonal antibody (MAb) E117-5 specific for Hib PS inhibited at a concentration of at least 80 microg/ml in vitro the adherence of Hib strain 770235f+b+ to oropharyngeal epithelial cells by 50% (P <, 0.02), but this MAb and sera from children immunized with Hib PS conjugate vaccine (n = 10) were not inhibitory in final dilutions containing up to 20 microg of anti-Hib PS per ml. The growth of Hib strain 770235f+b+ did completely stop in the presence of 5 microg of anti-Hib PS MAb E117-5 per ml and human sera with an anti-Hib PS concentration of 2 microg/ml or more, in contrast to the growth of the nonencapsular variant strain 770235f+b0.

Role of pili in Haemophilus influenzae adherence to, and internalization by, respiratory cells

To determine the role of pili in mediating adherence of type b and nontypeable Haemophilus influenzae to several respiratory cell types, piliated bacteria, nonpiliated phase variants, and nonpiliated mutants possessing insertionally inactivated pilin genes were tested. Both piliated and nonpiliated strains adhered to HeLa cells, nasal epithelial cells, A549 cells (type II pneumocyte-like cells), and two types of tracheal epithelial cells. Nonpiliated organisms adhered better than piliated variants to cultured HEp-2 cells, whereas piliated organisms adhered better than nonpiliated variants to bronchial epithelial cells and to shed buccal epithelial cells. GM1, a pilus receptor analog, inhibited pilus- but not nonpilus-mediated adherence. Piliated and nonpiliated H. influenzae were equally internalized by A549 cells. Thus, pili mediate adherence to some, but not all, cells derived from human respiratory tissues; nonpilus mechanisms contribute to both adherence, and internalization, of both piliated and nonpiliated organisms.

Progress towards a vaccine for nontypable Haemophilus influenzae

Nontypable Haemophilus influenzae is a common cause of human disease and is associated with significant morbidity and considerable societal cost. At present, measures to prevent nontypable H. influenzae disease are limited to prophylactic antibiotics and, on occasion, exogenous antibody preparations. However, because these interventions are often inadequate, there is interest in developing an effective vaccine. Given the marked diversity among epidemiologically unrelated strains and the frequent strain specificity of the immune response to infection, efforts have focused on identifying bacterial antigens that are highly conserved and capable of stimulating protective antibody. With the recent identification of several such antigens, attention must now turn toward selecting the appropriate combination of these molecules and determining the optimal strategy for their presentation to the immune system. The ultimate goal is to induce broad-based and long-lasting protection.

Attachment of Moraxella catarrhalis to pharyngeal epithelial cells is mediated by a glycosphingolipid receptor

Moraxella catarrhalis is one of the major pathogens of respiratory infections and has the ability to attach to the pharyngeal cells iva fimbriae. We characterized the epithelial cell receptor to which fimbriate M. catarrhalis binds. Neuraminidase pretreatment of pharyngeal epithelial cells resulted in a significant decrease of M. catarrhalis attachment, suggesting interaction with the sialic acid component. The attachment was not decreased in M. catarrhalis pretreated with 2 and 1 mg/ml of fucose, N-acetyl-neuraminic acid, N-acetyl-glucosamine, N-acetyl-galactosamine, acetyl-salicylic acid and colominic acid. However, M. catarrhalis treated with gangliosides M1, M2, D1a, D1b and T1a at a concentration of 2.5 micrograms/ml had significantly decreased the attachment compared to the control. In contrast treatment with gangliosides M3 and asialoganglioside M1 did not decrease the attachment of M. catarrhalis and thereby provided evidence for specificity of the inhibition. Concentration dependent effects of ganglioside M2 on the attachment were also observed. Other fimbriate isolates of M. catarrhalis showed decrease in attachment after treatment with ganglioside M2. However there was no effect on attachment when a nonfimbriate isolate was treated with ganglioside M2. This study indicates that the receptor of fimbriate M. catarrhalis on pharyngeal epithelial cells resides in the sequences of ganglioside M2.

Contribution of the major and minor subunits to fimbria-mediated adherence of Haemophilus influenzae to human epithelial cells and erythrocytes

Fimbriae are colonization factors of the human pathogen Haemophilus influenzae in that they mediate bacterial adherence to human eukaryotic cells. The contribution of the major (HifA) and putative minor (HifD and HifE) subunits of H. influenzae fimbriae to fimbria-specific adherence was studied by using mutants that were inactivated in distinct fimbrial genes. Both the major and minor subunits were required for adherence of H. influenzae to oropharyngeal epithelial cells and human erythrocytes carrying the AnWj antigen. Cloning of defined H. influenzae fimbrial genes in an Escherichia coli strain with type 1 fimbriae yielded recombinants expressing high amounts of HifA-containing H. influenzae fimbriae either with or without coexpression of both H. influenzae minor subunits. Both clones exhibited the specific adherence properties of H. influenzae fimbriae, implying that the minor H. influenzae subunits are dispensable for adherence and that the adhesive domain resides in the major subunit, HifA. In H. influenzae itself, the minor subunits probably affect adherence by raising the number of fimbriae above the minimal level required to establish adherence.

The HMW1 adhesin of nontypeable Haemophilus influenzae recognizes sialylated glycoprotein receptors on cultured human epithelial cells

Disease due to nontypeable Haemophilus influenzae begins with colonization of the upper respiratory tract mucosa. We recently reported that two surface-exposed high-molecular-weight proteins (HMW1 and HMW2) expressed by a prototypic strain of nontypeable H. influenzae mediate attachment to cultured epithelial cells. In the present study, we examined the nature of the epithelial cell receptor with which HMW1 interacts. Both proteinase K pretreatment and periodate oxidation of epithelial monolayers resulted in a marked decrease in HMW1-mediated binding, suggesting interaction with a glycoprotein structure. Treatment with peptide-N-glycosidase F produced a similar decrease in attachment and thereby provided further evidence for this conclusion. Desialylation of the epithelial cell surface also reduced binding, implying the presence of sialic acid in the receptor structure. Furthermore, lectins specific for terminal alpha 2-3-linked sialic acid were capable of inhibiting HMW1-mediated attachment. In summary, our results indicate that the HMW1 adhesin interacts with a glycoprotein receptor containing N-linked oligosaccharide chains with sialic acid in an alpha 2-3 configuration.

The fimbrial gene cluster of Haemophilus influenzae type b

Haemophilus influenzae infections are preceded by airway colonization, a process facilitated by fimbriae. Here, we identified the complete fimbrial gene cluster of H. influenzae type b. HifA forms the major subunit. HifB, a periplasmic chaperone, and HifC, an outer membrane usher, are typical assembly genes; their inactivation abolished fimbriae formation. HifD and HifE are putative minor subunits, both participating in fimbriae biogenesis. Inactivation of either one drastically reduced fimbriae expression. HifD represents a novel type of fimbrial subunit with lipoprotein characteristics, pointing to a membrane-associated function of HifD. Transcription of all fimbrial genes is coregulated through two clustered promoters. The flanking of the fimbrial gene cluster by repetitive extragenic palindromic sequences together with a partial duplication of an adjacent unrelated operon indicated that the cluster was once inserted in the H. influenzae genome as a mobile virulence unit.

Adaptive evolution of highly mutable loci in pathogenic bacteria

Bacteria have specific loci that are highly mutable. We argue that the coexistence within bacterial genomes of such 'contingency' genes with high mutation rates, and 'housekeeping' genes with low mutation rates, is the result of adaptive evolution, and facilitates the efficient exploration of phenotypic solutions to unpredictable aspects of the host environment while minimizing deleterious effects on fitness.

Phase variation of H. influenzae fimbriae: transcriptional control of two divergent genes through a variable combined promoter region

The expression of H. influenzae fimbriae is subject to reversible phase variation between three expression levels. This phenomenon is controlled at the transcriptional level of two divergently orientated genes, hifA and hifB, encoding the major fimbrial subunit and the fimbrial chaperone, respectively. The hifA and hifB promoter regions were found to be clustered through an almost complete divergent overlap with a variable DNA backbone of repetitive TA units. Variation in the number of units changes the normally strictly constrained spacing between the -35 and -10 sequences and controls the bidirectional transcription initiation, thus forming a novel mechanism directing multiple gene transcription.

Isolation, expression, and nucleotide sequencing of the pilin structural gene of the Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius

In this study we isolated the pilin gene from the Brazilian purpuric fever (BPF) clone of Haemophilus influenzae biogroup aegyptius, expressed the gene in Escherichia coli, and determined its nucleotide sequence. Comparison of the nucleotide sequence of the BPF pilin gene with the sequences of pilin genes from strains of H. influenzae sensu stricto demonstrated a high degree of identity. Consistent with this observation, hemagglutination inhibition studies performed with a series of glycoconjugates indicated that BPF pili and H. influenzae type b pili possess the same erythrocyte receptor specificity.

Changes in the structure of the cell surface carbohydrates of the chinchilla tubotympanum following Streptococcus pneumoniae-induced otitis media

Streptococcus pneumoniae (Spn) are among the most frequently isolated pathogens in acute otitis media (AOM) and in otitis media with effusion (OME). Recently, the specific receptor for Spn has been identified as the trisaccharide unit Gal beta 1-4 GlcNAc beta 1-3 Gal beta with GlcNAc beta 1-3 Gal beta as the principal binding site. During the colonization of mucosal surfaces, pneumococci produce a variety of enzymes. This study was conducted to identify any resulting changes in the cell surface carbohydrate structure due to the action of these enzymes during pneumococcal otitis media (OM) in chinchillas. Using a lectin histochemical method with seven different lectins (SNA, LFA, WGA, Succ WGA, BSL II, PNA, ECL), the labeling pattern revealed not only the removal of the terminal sialic acid, but also the exposure of N-acetyl-glucosamine. These results suggested that Spn-produced enzymes uncover part of their own receptor structure and thus may facilitate adherence and subsequent infection.