Interaction of Haemophilus influenzae with human erythrocytes and oropharyngeal epithelial cells is mediated by a common fimbrial epitope

Non-Typeable Haemophilus influenzae Invade Choroid Plexus Epithelial Cells in a Polar Fashion

Non-typeable Haemophilus influenzae (NTHI) is a pathogen of the human respiratory tract causing the majority of invasive H. influenzae infections. Severe invasive infections such as septicemia and meningitis occur rarely, but the lack of a protecting vaccine and the increasing antibiotic resistance of NTHI impede treatment and emphasize its relevance as a potential meningitis causing pathogen. Meningitis results from pathogens crossing blood-brain barriers and invading the immune privileged central nervous system (CNS). In this study, we addressed the potential of NTHI to enter the brain by invading cells of the choroid plexus (CP) prior to meningeal inflammation to enlighten NTHI pathophysiological mechanisms. A cell culture model of human CP epithelial cells, which form the blood-cerebrospinal fluid barrier (BCSFB) in vivo, was used to analyze adhesion and invasion by immunofluorescence and electron microscopy. NTHI invade CP cells in vitro in a polar fashion from the blood-facing side. Furthermore, NTHI invasion rates are increased compared to encapsulated HiB and HiF strains. Fimbriae occurrence attenuated adhesion and invasion. Thus, our findings underline the role of the BCSFB as a potential entry port for NTHI into the brain and provide strong evidence for a function of the CP during NTHI invasion into the CNS during the course of meningitis.

Capsule and fimbriae modulate the invasion of Haemophilus influenzae in a human blood-cerebrospinal fluid barrier model

The Gram-negative bacterium Haemophilus influenzae (H. influenzae) can commensally colonize the upper respiratory tract, but also cause life threatening disease including epiglottitis, sepsis and meningitis. The H. influenzae capsule protects the bacteria against both phagocytosis and opsonization. Encapsulated H. influenzae strains are classified into serotypes ranging from a to f dependent on their distinct polysaccharide capsule. Due to the implementation of vaccination the incidence of invasive H. influenzae type b (Hib) infections has strongly decreased and infections with other capsulated types, including H. influenzae type f (Hif), are emerging. The pathogenesis of H. influenzae meningitis is not clarified. To enter the central nervous system (CNS) the bacteria generally have to cross either the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BSCFB). Using a cell culture model of the BCSFB based on human choroid plexus papilloma (HIBCPP) cells and different H. influenzae strains we investigated whether Hib and Hif invade the cells, and if invasion differs between encapsulated vs. capsular-deficient and fimbriated vs. non-fimbriated variants. We find that Hib can adhere to and invade into HIBCPP cells. Invasion occurs in a strongly polar fashion, since the bacteria enter the cells preferentially from the basolateral "blood "side. Fimbriae and capsule attenuate invasion into choroid plexus (CP) epithelial cells, and capsulation can influence the bacterial distribution pattern. Finally, analysis of clinical Hib and Hif isolates confirms the detected invasive properties of H. influenzae. Our data point to roles of capsule and fimbriae during invasion of CP epithelial cells.

Occurrence of the Fimbria GenehifAin Clinical Isolates of NonencapsulatedHaemophilus influenzae

The adherence of Haemophilus influenzae to epithelial cells plays a crucial role in infections. However, little is known about the occurrence of fimbriae. In this study, we examined the distribution of the fimbria gene (hifA) by PCR among 167 H. influenzae strains isolated from patients with respiratory infections. Almost all (163; 98%) of the isolates were nonencapsulated strains. The carriage rate of hifA by the nonencapsulated strains was 18.4%. Electron microscopy showed that fimbriae were abundantly present on the cell surface of hifA-positive strains tested. Only four (2.4%) isolates were encapsulated, all of which were type b and did not possess hifA. The present work suggests that fimbriae may play a considerable role as adhesins in nonencapsulated H. influenzae strains.

Gr-1highPolymorphonuclear Leukocytes and NK Cells Act via IL-15 to Clear IntracellularHaemophilus influenzaein Experimental Murine Peritonitis and Pneumonia

Polymorphonuclear leukocytes (PMNs) can be divided into Gr-1(high) and Gr-1(low) subpopulations, but the differences in the functions of these cells in the host are unknown. This study investigated the roles of these two cell populations in the clearance of an intracellular pathogen (Haemophilus influenzae) causing murine peritonitis and pneumonia. Microarray analysis and quantitative real-time PCR analysis of proteose peptone-elicited peritoneal murine PMNs showed that IL-15 mRNA levels were significantly higher in Gr-1(high) PMNs than in Gr-1(low) PMNs. In addition, IL-15 was produced only by Gr-1-positive PMNs, especially Gr-1(high) PMNs. IL-15 was required for efficient clearance of experimental murine H. influenzae pneumonia, as 4 days postinfection lungs from IL-15 knockout mice contained 50- to 100-fold more bacteria than did wild-type mouse lungs. Gr-1 PMN-depleted C57BL/6 mice were more susceptible to H. influenzae pneumonia than were Gr-1 PMN replete C57BL/6 mice or C57BL/6 nude mice, demonstrating that Gr-1 PMNs are important in the clearance of intracellular bacteria. IL-15-activated NK cells killed H. influenzae in PMNs. Flow cytometry confirmed the expression of CD69 on the cell membrane of IL-15-activated NK cells. Our results show that Gr-1(high) PMNs produce more IL-15 than Gr-1(low) PMNs, and that IL-15-activated NK cells protect against early infection by H. influenzae.

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.

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.

Comparative evaluation of conjugate vaccines in theHaemophilus influenzaeinfection model

We used a murine model of Haemophilus influenzae type b (Hib) infection to analyze the immunologic response to two commercially available PRP conjugate vaccines (HbOC, PRP-T). The mortality rate in mice infected with a large dose of the bacteria after vaccination with HbOC or PRP-T at two and three doses was significantly lower than in non-vaccinated mice and mice vaccinated by one dose. Furthermore, for infections caused by a small bacterial dose, the mortality rate in mice vaccinated with one, two, or three doses was significantly lower than in non-vaccinated mice. The induction level of anti-PRP antibodies, especially IgG, in serum of mice vaccinated by two or three doses was higher than in those vaccinated with a single dose. Our results indicate that the dose of vaccine influences its efficacy in protecting against Hib infection. Our results also showed a lack of difference between two different PRP conjugate vaccines.

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.

Nucleotide sequences of genes coding for fimbrial proteins in a cryptic genospecies of Haemophilus spp. isolated from neonatal and genital tract infections

Nineteen isolates belonging to a cryptic genospecies of Haemophilus (referred to here as genital strains) isolated from genital tract infections (6 strains) and from neonatal infections (13 strains) were studied for fimbrial genes. Sixteen strains exhibit peritrichous fimbriae observed by electron microscopy. By PCR with primers corresponding to the extreme ends of the Haemophilus influenzae type b (Hib) hifA and hifD genes and Southern blotting, a hifA-like gene (named ghfA) and a hifD-like gene (named ghfD) were identified in 6 of the 19 strains. Five of these six strains were from the genital tracts of adults, and one was from a neonate. For each gene, the nucleotide sequence was identical for the six strains. A hifE-like gene (named ghfE) was amplified from only one of the 19 genital strains of Haemophilus, but the ghfE probe gave a signal in Southern hybridization with the five other strains positive for ghfA and ghfD. Therefore, these strains may carry a ghfE-like gene. The Hib fimbrial gene cluster is located between the purE and pepN genes as previously described. For the 13 genital Haemophilus strains that lack fimbrial genes, this region corresponds to a noncoding sequence. Another major fimbrial gene designated the fimbrin gene was previously identified in a nontypeable H. influenzae strain. A fimbrin-like gene was identified for all of our 19 genital strains. This gene is similar to the ompP5 gene of many Haemophilus strains. Therefore, other, unidentified genes may explain the piliation observed in electron microscopy on genital Haemophilus strains which do not possess LKP-like fimbrial genes. Fimbrial genes were significantly associated with strains isolated from the genital tract. They may confer on the strain the ability to survive in the genital tract.

Microbiology of bacterial respiratory infections

The upper respiratory tract may become susceptible to bacterial infection as a result of health conditions such as allergies and viral infections, as well as the effects of smoking and airborne environmental pollutants. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the most common bacterial pathogens in upper and lower respiratory tract infections. Streptococcus pyogenes is the predominant bacterial pathogen in pharyngitis and tonsillitis. Bacterial pathogens adhere to mucous membranes and colonization ensues. In an otherwise healthy individual the host immune system responds to the invading bacteria resulting in edema and swelling. If antimicrobial treatment does not eradicate the invading organisms and successfully interrupt the progress of the infection, the patient may develop recurrent or chronic disease. S. pneumoniae and other pathogens once susceptible to penicillin and other antibiotics are now becoming resistant. Bacterial resistance has developed and disseminated because of the widespread use of antibiotics. Major mechanisms of bacterial resistance to antimicrobials in upper respiratory tract infections include enzymatic inhibition, membrane impermeability, alteration of target enzymes, active pumping out of antibiotic and alteration of the ribosomal target.

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.

Vaccination against middle-ear bacterial and viral pathogens

Considerable evidence suggests that otitis media (OM) can be prevented by systemic immunization. Building on the highly effective H. influenzae type b (Hib) conjugate vaccine technology, pneumococcal conjugate vaccines are being developed to circumvent T-independence of these antigens and provide durable immunity at a very young age. Several pneumococcal conjugate vaccines are currently in clinical testing. Potential vaccine antigens of nontypable H. influenzae (NTHi) include OMP, HMW, pili, and fimbriae. Several OMPs show extensive homology among strains, but surface, determinants of others are highly variable so that antibodies to surface epitopes of one strain will not bind to surface epitopes of another. Several M. catarrhalis OMP and HMW antigens have vaccine potential, but no functional correlates of protection have been identified, and there is no clear evidence that antibody to M. catarrhalis is associated with OM protection. Attenuated viral vaccines also hold promise of preventing childhood OM. Two clinical trials with killed influenza vaccines have shown a significant reduction in OM among vaccine recipients compared to control children during periods of high influenza disease activity in the community. Passive immunoprophylaxis also has potential for preventing OM. Human bacterial polysaccharide immune globulin was protective for pneumococcal OM in children and in the chinchilla OM model. High-dose respiratory syncytial virus-enriched immunoglobulin reduced the incidence and severity of RSV lower respiratory tract infection in high-risk children. Passive immunoprophylaxis may also be effective in children with specific immune deficiencies, such as IgG2 deficiency, and patients who fail to respond to vaccines.

Identification of two minor subunits in the pilus of Haemophilus influenzae

Haemophilus influenzae type b (Hib) organisms produce pili, which mediate attachment to human cells and are multimeric structures composed of a 24-kDa subunit called pilin or HifA. Although pili from other organisms contain additional proteins accessory to pilin, no structural components other than pilin have been identified in Hib pili. Previous analysis of a Hib pilus gene cluster, however, suggested that two genes, hifD and hifE, may encode additional pilus subunits. To determine if hifD and hifE encode pilus components, the genes were overexpressed in Escherichia coli and the resulting proteins were purified and used to raise polyclonal antisera. Antisera raised against C-terminal HifD and HifE fragments reacted with H. influenzae HifD and HifE proteins, respectively, on Western immunoblots. Western immunoblot analysis of immunoprecipitated Hib pili demonstrated that HifD and HifE copurified with pili. In enzyme-linked immunosorbent assays, antisera raised against a recombinant HifE protein that contained most of the mature protein reacted more to piliated Hib than to nonpiliated Hib or to a mutant containing a hifE gene insertion. Immunoelectron microscopy confirmed that the HifE antiserum bound to pili and demonstrated that the antiserum bound predominantly to the pilus tips. These data indicate that HifD and HifE are pilus subunits. Adherence inhibition studies demonstrated that the HifE antiserum completely blocked pilus-mediated hemagglutination, suggesting that HifE mediates pilus adherence.

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.

Paracytosis of Haemophilus influenzae through cell layers of NCI-H292 lung epithelial cells

Haemophilus influenzae penetrates the respiratory epithelium during carriage and invasive disease, including respiratory tract infections. We developed an in vitro model system consisting of lung epithelial NCI-H292 cells on permeable supports to study the passage of H. influenzae through lung epithelial cell layers. The NCI-H292 cells formed tight layers with a Ca(2+)-dependent transepithelial resistance of around 40 omega.cm2. H. influenzae passed through the cell layers without affecting the viability of the cells and [3H]inulin penetration. The passage time was independent of the inoculum of H. influenzae in the apical compartment and was not influenced by the presence of capsule or fimbriae on H. influenzae or by the ability of the bacteria to adhere to the epithelial cells. However, highly adherent strains showed greater paracytosis. Different strains passed through the cell layer independently. The passage time was shorter for rapidly growing strains than for slowly growing strains (10 to 18 h and 30 h, respectively). Microscopic examination revealed the presence of clusters of H. influenzae bacteria between the epithelial cells, indicating that bacterial passage was due to paracytosis. After the addition of chloramphenicol, no bacteria were cultured from the basolateral side, and no bacterial clusters between the epithelial cells were seen, suggesting that de novo bacterial protein synthesis was needed for the bacteria to reach the intercellular space. We conclude that H. influenzae passes through viable cell layers of the human lung epithelial cell line NCI-H292 by paracytosis, requiring bacterial protein synthesis.

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.

Binding of Haemophilus influenzae to purified mucins from the human respiratory tract

Mucins are high-molecular-weight glycoproteins and major constituents of the mucus layer which covers the airway surface. We have studied the interactions between bacteria, mucins, and epithelial cells from the human respiratory tract. Nontypeable strains of Haemophilus influenzae were found to bind to purified airway mucins in suspension and on solid phase. Mucins in suspension inhibited the attachment of these strains to nasopharyngeal epithelial cells, while mucin coating of the cells enhanced their binding. In contrast, strains of Streptococcus pneumoniae and encapsulated and other nontypeable H. influenzae strains failed to interact with mucins. These H. influenzae strains used other strategies for adherence to epithelial cells. The type b strain 770235 attached via fimbriae but also expressed a subcapsular adhesin that was detected in a capsule- and fimbria-defective mutant. Mucin pretreatment of these bacteria did not inhibit adherence, but mucin pretreatment of epithelial cells inhibited adherence, probably by shielding of the receptors for these adhesins. Non-mucin-binding nontypeable and encapsulated H. influenzae strains would, therefore, adhere only after disruption of the mucus layer and exposure of cellular receptors. Differences in tissue toxicity and invasiveness among H. influenzae strains may also be influenced by the mucin interactions of the strains.

Evidence that surface fibrils expressed by Haemophilus influenzae type b promote attachment to human epithelial cells

Haemophilus influenzae type b is a Gram-negative bacillus that initiates infection by colonizing the upper respiratory tract. Previous studies have established that H. influenzae haemagglutinating pili possess adhesive properties and influence the process of colonization. Additional studies suggest the presence of a second H. influenzae adhesin distinct from haemagglutinating pili. In the present study, we examined a non-piliated H. influenzae type b strain by transmission electron microscopy and visualized occasional short, thin, surface fibrils. Subsequently, we isolated a spontaneous mutant that lacked surface fibrils and was deficient in adherence to cultured human epithelial cells. Using a cloning strategy that exploited this mutant, we isolated a fragment of DNA that promotes in vitro adherence to human epithelial cells when expressed in laboratory strains of Escherichia coli. Mutagenesis of this fragment in a series of H. influenzae type b strains resulted in loss of expression of surface fibrils and a marked decrease in attachment. Furthermore, restoration of surface fibril expression was associated with reacquisition of wild-type levels of adherence. Our results are consistent with the conclusion that H. influenzae type b surface fibrils have adhesive capacity. We speculate that these organelles facilitate colonization of the human respiratory tract.

A Haemophilus influenzae IgA protease-like protein promotes intimate interaction with human epithelial cells

Haemophilus influenzae represents a common cause of human disease and an important source of morbidity and mortality. Disease caused by this organism begins with colonization of the upper respiratory tract. Several studies indicate that H. influenzae is capable of binding to and entering cultured human cells, properties which are potentially of relevance to the process of colonization. In the present study, we isolated an H. influenzae gene designated hap, which is associated with the capacity for in vitro attachment and entry. Analysis of the derived amino acid sequence of hap demonstrated significant homology with the serine-type IgA1 proteases expressed by H. influenzae and Neisseria gonorrhoeae. It is notable that the hap product shares the catalytic domain of the IgA1 proteases and appears to be processed and secreted in an analogous manner. We speculate that the hap gene product is an important determinant of colonization, perhaps enabling the organism to evade the local immune response and thereby persist within the respiratory tract.

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.

Quantitative flow cytometric analysis of opsonophagocytosis and killing of nonencapsulated Haemophilus influenzae by human polymorphonuclear leukocytes

Since nonencapsulated Haemophilus influenzae persists in the lower respiratory tracts of patients with chronic bronchitis despite the presence of specific antibodies, complement, and polymorphonuclear leukocytes (PMNs), opsonophagocytosis of H. influenzae was analyzed. Nonencapsulated H. influenzae isolated from the sputa of chronic bronchitis patients was labeled with fluorescein isothiocyanate and incubated with human PMNs in the presence of complement and antibodies for 30 min at 37 degrees C. Candida albicans was added to each sample as an internal standard, and the reduction of the number of bacteria was determined by flow cytometry. Fluorescence quenching with ethidium bromide was used to discriminate between intracellular and extracellular bacteria. Opsonophagocytosis of viable H. influenzae d1 was 17% +/- 29% in the presence of complement and human pooled sera containing high titers of strain-specific antibodies. Opsonophagocytosis of six other H. influenzae strains was also poor. Under the same conditions, opsonophagocytosis of Staphylococcus aureus was 90% +/- 5%, and opsonophagocytosis of C. albicans was 55% +/- 23%. About half of the number of H. influenzae bacteria associated with PMNs was internalized. Opsonophagocytosis of heat-killed H. influenzae d1 (41% +/- 20%) was higher than that of viable bacteria of the same strain (P < 0.05). This result suggests that the accessibility of epitopes on H. influenzae for opsonizing antibodies is better on killed than on viable bacteria. We conclude that viable nonencapsulated H. influenzae is poorly opsonophagocytized in the presence of strain-specific antibodies and complement.

Opsonic antibodies to outer membrane protein P2 of nonencapsulated Haemophilus influenza are strain specific

The ability of monoclonal antibodies (MAbs) specific for variable and conserved epitopes of outer membrane protein (OMP) P2 (b,c) of nonencapsulated Haemophilus influenza to promote opsonophagocytosis of this bacterium by human polymorphonuclear leucocytes (PMNs) was determined by flow cytometry. MAbs rendering PMNs fluorescent because of association with fluorescein isothiocyanate-labelled bacteria were defined as stimulating opsonophagocytosis. Opsonophagocytosis was dependent on the presence of both antibodies and complement. Of the 14 MAbs directed to the variable parts of OMP P2 (L. van Alphen, P. Eijk, L. Geelen-van den Broek, and J. Dankert, Infect. Immun. 59:247-252, 1991), 9 stimulated opsonophagocytosis. Four of the five nonopsonophagocytic MAbs that were immunoglobulin G1 were unable to cause complement activation. The MAbs promoting opsonophagocytosis included MAbs specific for one or more OMP P2 antigenic variants of H. influenzae strains isolated from patients with chronic bronchitis during persistent infection. MAbs cross-reacting in enzyme-linked immunosorbent assays with nonrelated H. influenzae did not promote opsonophagocytosis of strains from other patients. Opsonophagocytosis was not observed in the presence of three MAbs reacting with OMP P2 epitopes common in H. influenzae. These results indicate that OMP P2-dependent opsonophagocytosis of nonencapsulated H. influenzae is strictly strain specific.

Adherence to human cells of a cryptic Haemophilus genospecies responsible for genital and neonatal infections

Haemophilus strains usually identified as Haemophilus influenzae biotype IV belonging to a cryptic genospecies are responsible for genital and neonatal infections. As a first approach to identifying the bacterial factors involved in the pathogenesis of these unusual diseases, we studied the piliation, adherence, and invasion properties of 17 strains assigned to this cryptic genospecies. Twelve strains spontaneously displayed abundant peritrichous piliation, and two strains expressed peritrichous pili after enrichment procedures. For virtually all strains, piliation correlated with adhesion to cultured HeLa cells of genital origin and to a lesser extent with adhesion to HEp-2 cells of laryngeal origin. A variation in the adherence properties of the various strains was observed: all piliated strains except one adhered to 50 to 100% of HeLa cells, with a mean number of bacteria per cell varying from 4 to 50. Adherence was not dependent on the state of growth for most strains, was more pronounced with HeLa cells than with HEp-2 cells for 10 of the 12 highly adherent strains, was time and inoculum dependent, and was not followed by significant invasion of cells. Most of the strains belonging to this unusual Haemophilus clone possess adhesins that do not recognize erythrocyte receptors, since agglutination of human erythrocytes was observed with only 3 of the 14 piliated strains.

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.

Construction of chimaeric genes for mapping a surface-exposed epitope on the pilus of non-typable Haemophilus influenzae strain M37

A murine monoclonal antibody (mAb), designated 3H12, reacts with a surface-exposed conformational epitope on the pilus of non-typable Haemophilus influenzae strain M37. This antibody does not recognize the related pilus from H. influenzae type b, strain MinnA. Although mAb 3H12 does not recognize strain M37 pilin on Western blots, mAb 3H12 recognizes the recombinant M37 pilin protein expressed by Escherichia coli. In order to map the epitope recognized by mAb 3H12, we constructed a series of chimaeric genes. The chimaeric genes were expressed in E. coli and the chimaeric proteins characterized with respect to their reactivity with mAb 3H12. Residues between 37 and 100 of the M37 pilin protein are essential for the expression of the mAb 3H12 epitope. Residues in the carboxyl half of the M37 protein enhance the reactivity of mAb 3H12 when expressed in the presence of residues 37-100. Construction of chimaeric genes may provide a general methodology for mapping of conformational epitopes expressed by one of a related pair of proteins.

Fimbriae and membranes on Haemophilus parasuis

In the electron microscope an additional layer (glycocalix) of the cell wall and fimbriae on Haemophilus parasuis were shown in thin sections of the infected CAM which have their origin on the CM of the Haemophilus parasuis-cells. No fimbriation was seen after conventional cultivation.

The other mediator for adherence of Haemophilus influenzae organisms without involvement of fimbriae

The number of the nontypeable Haemophilus influenzae (HiN) organisms that adhered to the primary mouse fetal lung cells was significantly more than type b Haemophilus influenzae (Hib) organisms. The average number of HiN organisms adherent to host cells was 2,291/100 host cells (range, 1,654-3,182), but that of Hib was markedly reduced to 147/100 host cells (range, 102-238). In this case, P value was less than 0.05 by using a paired Student t-test. The sonicated extract from HiN TMS11 organisms inhibited adherence of H. influenzae TMS11 organisms to monolayer at 76.3% and it inhibited adherence of Hib TMS24 organisms at 92.3%. This result indicates that a mediator existing on the surface of HiN organisms may be the same as that on type b organisms. The number of detected organisms in broncho and lung tissues 3 days after intranasal infection with HiN strains was significantly greater than that in infection with Hib strains. Therefore, in vitro adhesive capacity of H. influenzae organisms was correlative to infectivity by intranasal injection.

Comparison and analysis of the nucleotide sequences of pilin genes from Haemophilus influenzae type b strains Eagan and M43

Previous studies have demonstrated antigenic differences among the pili expressed by various strains of Haemophilus influenzae type b (Hib). In order to understand the molecular basis for these differences, the structural gene for pilin was cloned from Hib strain Eagan (p+) and the nucleotide sequence was compared to those of strains M43 (p+) and 770235 b0f+, which had been previously determined. The pilin gene of Hib strain Eagan (p+) had a 648-bp open reading frame that encoded a 20-amino-acid leader sequence followed by the 196 amino acids found in mature pilin. The translated sequence was three amino acids larger than pilins of strains M43 (p+) and 770235 b0f+ and was 78% identical and 95% homologous when conservative amino acid substitutions were considered. Differences between the amino acid sequences were not localized to any one region but rather were distributed throughout the proteins. Comparison of protein hydrophilicity profiles showed several hydrophilic regions with sequences that were conserved between strain Eagan (p+) and pilins of other Hib strains, and these regions represent potentially conserved antigenic domains. Southern blot analyses using an intragenic probe from the pilin gene of strain Eagan (p+) showed that the pilin gene was conserved among all type b and nontypeable strains of H. influenzae examined, and only a single copy was present in these strains. Homologous genes were not present in the phylogenetically related species Pasteurella multocida, Pasteurella haemolytica, and Actinobacillus pleuropneumoniae. These data indicate that the pilin gene was highly conserved among different strains of H. influenzae and that small differences in the pilin amino acid sequences account for the observed antigenic differences of assembled pili from these strains.

Interactions of Haemophilus influenzae with cultured human endothelial cells

The interactions of capsulate (b+) and capsule-deficient (b-) Haemophilus influenzae type b with endothelial cells were studied in vitro using human umbilical vein endothelial cells (Huvecs). Association was determined by estimation of colony forming units (cfu) as well as the binding of 3H-thymidine-labelled bacteria. Bacteria associated with Huvecs rapidly and in a dose-dependent manner. The presence of capsule on bacteria resulted in a decrease in the rate of cell-association. Internationalisation of bacteria by Huvecs was quantitated after elimination of extracellular bacteria with gentamicin. It was found that larger numbers of b- bacteria were internalised compared to b+ bacteria. Incubation in the presence of metabolic inhibitors had little effect on the association of bacteria to Huvecs whereas internalisation was dependent on the integrity of host cellular functions. Electron microscopic studies confirmed phagocytic ingestion of both b+ and b- variants and suggested that the majority of the internalised bacteria remained viable within endothelial cell vacuoles. Haemophilus influenzae were translocated within vacuoles both from the apical to basal and the basal to apical direction.

Effect of fusafungine on adherence of Haemophilus influenzae type b to human epithelial cells in vitro

Haemophilus influenzae, a normal host of the nasopharynx of humans, may become a pathogen. The first step of infection is adherence to epithelial cells of the nasopharynx through glycopeptidic adhesins, or pili. Adherence to human epithelial cells in continuous lines, HeLa and Hep2, of 8 piliated strains of Haemophilus influenzae isolated from human infections of the respiratory tract was studied in vitro in the presence of fusafungine, a local bacteriostatic antibiotic. When the bacteria were grown in the presence of 0.5 x the MIC, fusafungine afforded 45-75% of adherence inhibition, but this inhibitory effect did not parallel the MICs. In contrast, no significant effect could be observed either when epithelial cells were exposed to 0.5 x the MIC before use in the adherence assay, or when this assay was performed in the presence of 0.5 x the MIC of fusafungine. The partial adherence inhibition observed suggests that fusafungine interacts with the bacterial binding sites but that other mechanisms may contribute to the inhibitory process. This effect of fusafungine should prevent but not eradicate colonization of the nasopharyngeal mucosa by Haemophilus influenzae and may account for the therapeutic efficacy reported in infections of the respiratory tract due to Haemophilus influenzae.

Immunochemical characterization of variable epitopes of outer membrane protein P2 of nontypeable Haemophilus influenzae

Monoclonal antibodies (MAbs) were elicited to the nontypeable Haemophilus influenzae variants d1 to d4, which differ in the outer membrane protein P2 to analyze the immunological properties of the variable parts of this protein. Five MAbs reacted in a whole-cell enzyme-linked immunosorbent assay (ELISA) only with the homologous strain and in some cases with its variants, but not with 69 unrelated nonencapsulated H. influenzae isolates; nine MAbs also reacted with some other H. influenzae isolates, and four MAbs showed broad cross-reactivity. All of the MAbs reacted with purified protein P2 in ELISAs and immunoblotting. The five MAbs which reacted with the homologous strain d3 and not with the variants d1, d2, and d4 promoted complement-dependent bactericidal activity against strain d3. These and four other MAbs reacted with the intact bacteria of strain d3 in immunogold electron microscopy, indicating that they were directed against surface-exposed epitopes of outer membrane protein P2. A mutant of strain d3 was isolated as a survivor from bacterial killing by complement and MAb 30DA5. This mutant had an altered P2 protein on sodium dodecyl sulfate-polyacrylamide gels and had lost its reactivity with all of the five H. influenzae d3-specific MAbs but not with the other MAbs. From these results, we conclude that the variable parts of outer membrane protein P2 of nonencapsulated H. influenzae from the sputum of patients with chronic obstructive pulmonary disease are immunogenic and mostly surface exposed. Only strain-specific MAbs promoted complement-dependent killing of the bacteria, which was abolished in a spontaneous mutant with an altered P2 protein.

Purification and characterization of an outer membrane protein adhesin from Haemophilus parainfluenzae HP-28

Outer membranes were isolated from Haemophilus parainfluenzae HP-28 by a mild extraction method followed by Sephadex G-150 gel filtration chromatography. The first peak (pool 1) recovered contained an activity which inhibited adherence of HP-28 cells to saliva-coated spheroidal hydroxyapatite. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of pool 1 revealed a dominant protein band of 34 kDa. The SDS-PAGE-purified 34-kDa protein was excised from the gel and used for antibody preparation in rabbits. The antiserum produced was analyzed by immunoblot and was shown to be monospecific for the 34-kDa protein. Anti-34-kDa protein antibody was purified from the rabbit antiserum by protein A-Sepharose 6MB affinity chromatography. This antibody was then cross-linked to protein A-Sepharose 6MB to construct a second affinity column. The 34-kDa proteins were purified from outer membranes by this affinity chromatography. The 34-kDa protein was homogeneous, as confirmed by SDS-PAGE, isoelectric focusing, and reverse-phase chromatography analyses. Fab and Fc fragments of the purified anti-34-kDa protein antibodies were prepared by papain digestion, followed by carboxymethyl cellulose chromatography. Fab fragments from the anti-34-kDa protein antibody and the affinity-purified 34-kDa protein both showed significant inhibition of parent H. parainfluenzae HP-28 cell adherence to experimental salivary pellicle and to Streptococcus sanguis SA-1.

Combined inheritance of epithelial and erythrocyte receptors for Haemophilus influenzae

Haemophilus influenzae type b expressing fimbriae showed no adherence to buccal epithelial cells and no agglutination of erythrocytes from three AnWj-negative siblings in one family. Hemagglutination of erythrocytes from 13 AnWj-positive members of the same family and from 24 controls was normal, and H. influenzae adhered well to buccal epithelial cells from them. These data indicate that the expression of epithelial and erythrocyte receptors for H. influenzae is inherited concomitantly. Combined with previous data (L. van Alphen, J. Poole, L. Geelen, and H. Zanen, Infect. Immun. 55:2355-2358, 1987), the results show that the receptor molecules on the surfaces of the epithelial cell and the erythrocyte are different but that the binding sites for the fimbriae of H. influenzae are similar.

Purification and characterization of a pilin specific for Brazilian purpuric fever-associated Haemophilus influenzae biogroup aegyptius (H. aegyptius) strains

Brazilian purpuric fever (BPF) is a recently described fatal pediatric disease caused by systemic infection with Haemophilus influenzae biogroup aegyptius. Previous studies have shown that all H. influenzae biogroup aegyptius strains isolated from BPF cases and case contacts share several unique phenotypic and genotypic characteristics that differentiate them from other H. influenzae biogroup aegyptius strains isolated from conjunctivitis cases in Brazil. One key characteristic of this BPF clone is reactivity in a BPF-specific monoclonal antibody enzyme-linked immunosorbent assay. We have purified and partially characterized a pilin, referred to as the 25-kilodalton (kDa) protein. Aggregates of this protein contain a heat-labile epitope which is recognized by a monoclonal antibody used in the BPF-specific enzyme-linked immunosorbent assay. The protein has a molecular weight of approximately 25,000, is insoluble in most detergents, and fractionates with outer membrane vesicles after LiCl extraction. Biochemical analysis of the 25-kDa protein shows it to have an amino acid composition similar but not identical to that of the H. influenzae type b pilin. The sequence of 20 N-terminal amino acids of the 25-kDa protein shows almost complete homology with the N terminus of the H. influenzae type b pilin and the types 1 and P pilins of Escherichia coli. Transmission electron microscopic analysis of the purified protein shows the presence of filamentous structures similar in morphology to those of H. influenzae pili. Reactivity between the 25-kDa protein and the BPF-specific monoclonal antibody is demonstrated by Western blotting (immunoblotting) and colloidal gold-enhanced immunoelectron microscopy. Hemadsorption analysis shows that expression of this protein is associated with increases in piliated cells and enhanced binding of these cells to human erythrocytes. These studies indicate that expression of the 25-kDa protein is a characteristic unique to the BPF clone and suggest that this protein plays a role in the pathogenesis of BPF.

In vivo and in vitro expression of outer membrane components of Haemophilus influenzae

The outer membrane protein composition of Haemophilus influenzae grown under a variety of culture conditions including growth in sputum and serum, and intraperitoneally in rats was analyzed. The pattern of the major outer membrane proteins, a, b,c, d, e and P6 remained very similar under all these conditions. Outer membrane proteins expressed during iron limitation were also expressed in bacteria growing in rats, in serum or in sputum. To determine the expression of the major outer membrane proteins and lipopolysaccharide in patient materials (sputum, cerebrospinal fluid, postmortem tissue) monoclonal antibodies specific for the outer membrane proteins a, b,c, d and P6 as well as lipopolysaccharide were used in immunoblotting. They showed the same reaction patterns with bacteria in the patient materials as with the bacteria isolated from these specimens. We conclude that the major outer membrane components expressed under in vitro conditions are also expressed in various clinical materials during infection.

Adherence of skin bacteria to human epithelial cells

Aerobic and anaerobic bacteria isolated from human axillae were tested for their capacity to adhere to buccal epithelial cells, immortalized human epithelial (HEp-2) cells, and undifferentiated and differentiated human epithelial cells. In general, both aerobic and anaerobic diphtheroids adhered better to differentiated human epithelial cells than to HEp-2 and undifferentiated human epithelial cells (P less than 0.05). Mannose, galactose, fucose, N-acetyl-D-glucosamine, and fibronectin were also assayed for their capacity to inhibit the adherence of diphtheroids to human epithelial cells. A great deal of variability was observed in the capacity of the latter compounds to inhibit the attachment of aerobic diphtheroids to undifferentiated and differentiated epithelial cells. Overall, mannose appeared to be best at inhibiting the adherence of the aerobic diphtheroids to undifferentiated human epithelial cells. Galactose, fucose, N-acetyl-D-glucosamine, and fibronectin showed a greater capacity to inhibit attachment of aerobic diphtheroids to differentiated than to undifferentiated human epithelial cells. The inhibition of adherence to differentiated human epithelial cells varied with the microorganism and the compound tested; however, the highest and most consistent inhibition of adherence (76.1 to 88.6%) was observed with a 5% solution of N-acetyl-D-glucosamine. The in vitro adherence and adherence inhibition assays presented here demonstrate that a number of adhesins and receptors are involved in the adherence of skin bacteria to human epithelial cells and receptors on human epithelial cells are apparently altered during differentiation.

Relationship of Haemophilus influenzae type b pilus structure and adherence to human erythrocytes

Six strains of Haemophilus influenzae type b, some expressing immunologically different pili, showed identical patterns of binding to erythrocytes that were characterized for 38 blood group antigens. All six strains appeared to bind to the Anton antigen, as they agglutinated all erythrocytes tested except cord erythrocytes and those characterized as Lu(a-b-), dominant type, including Anton-negative cells.

Antigenic drift of Haemophilus influenzae in patients with chronic obstructive pulmonary disease

Differences in the major outer membrane protein b,c (molecular weight, 39,000 to 41,000) of related Haemophilus influenzae strains isolated from the sputum of patients with chronic obstructive pulmonary disease were analyzed biochemically and immunologically. Protein b,c was isolated from a total of six related H. influenzae strains from two chronic obstructive pulmonary disease patients. After CNBr digestion of the proteins, the differences in size appeared in the larger of the two fragments. Trypsin and chymotrypsin digests of proteins from related H. influenzae strains showed that proteins differed by only a few peptides or were very similar, in contrast to the peptide maps of proteins from nonrelated strains. Peptide analysis of b,c proteins from related H. influenzae strains by high-performance liquid chromatography after Staphylococcus aureus V8 protease digestion and amino acid analysis of corresponding fractions revealed highly comparable patterns, indicating only minor differences in the amino acid sequences of these proteins. Immunization of rabbits with intact bacteria of four related H. influenzae strains resulted in a strong anti-protein b,c antibody response in all animals. In three of four rabbits, antibodies specific for the b,c protein of the strain used for immunization were elicited, indicating that the changed proteins contained specific immunodominant epitopes. Anti-protein b,c antibodies promoted strain-specific, complement-dependent, bactericidal activity. From these results, we conclude that H. influenzae shows antigenic drift in immunodominant epitopes, caused by small changes in amino acid composition of the b,c protein. Antibodies to these epitopes promote complement-dependent bactericidal activity.

Nonculture detection of Haemophilus influenzae in sputum with monoclonal antibodies specific for outer membrane lipoprotein P6

Isolation of Haemophilus influenzae from sputum is hampered by overgrowth by other microorganisms or by antibiotic treatment of the patient. To overcome this problem in the detection of H. influenzae, an in situ immunoperoxidase staining technique was developed with monoclonal antibody (MAb) 8BD9, immunoglobulin subclass G2a. MAb 8BD9 appeared to be directed to an epitope on the outer membrane lipoprotein P6 of H. influenzae. The species specificity of MAb 8BD9 was analyzed by staining isolates from different bacterial species. MAb 8BD9 reacted with all 300 H. influenzae strains tested and with H. aegyptius and H. haemolyticus. Twenty-six of 30 H. parainfluenzae strains, other Haemophilus species, and other bacterial species often isolated from sputum were not stained. The staining technique was compared with culture of 845 routinely obtained sputum samples from patients with respiratory tract infections. In 829 sputa (98.1%), the results of both techniques were in agreement; 173 were positive for H. influenzae, and 656 were negative. With 14 sputum samples, the staining method gave a positive result for H. influenzae, but the bacterium was not cultured. This could be ascribed to antibiotic treatment of the patient (n = 7), the presence of other MAb 8BD9-positive Haemophilus species in the sputum (n = 5), and overgrowth by swarming Proteus mirabilis or by Branhamella catarrhalis. In the immunoperoxidase- and Gram-stained smears of two sputum samples, no bacteria were seen, although some H. influenzae was cultured. On the basis of these results, we conclude that immunoperoxidase staining with MAb 8BD9 is a fast and reliable extension of the available detection techniques for H. influenzae.