Development of novel isatin-nicotinohydrazide hybrids with potent activity against susceptible/resistant Mycobacterium tuberculosis and bronchitis causing-bacteria

Joining the global fight against Tuberculosis, the world's most deadly infectious disease, herein we present the design and synthesis of novel isatin-nicotinohydrazide hybrids (5a-m and 9a-c) as promising anti-tubercular and antibacterial agents. The anti-tubercular activity of the target hybrids was evaluated against drug-susceptible M. tuberculosis strain (ATCC 27294) where hybrids 5d, 5g and 5h were found to be as potent as INH with MIC = 0.24 µg/mL, also the activity was evaluated against Isoniazid/Streptomycin resistant M. tuberculosis (ATCC 35823) where compounds 5g and 5h showed excellent activity (MIC = 3.9 µg/mL). Moreover, the target hybrids were examined against six bronchitis causing-bacteria. Most derivatives exhibited excellent antibacterial activity. K. pneumonia emerged as the most sensitive strain with MIC range: 0.49-7.81 µg/mL. Furthermore, a molecular docking study has proposed DprE1 as a probable enzymatic target for herein reported isatin-nicotinohydrazide hybrids, and explored the binding interactions within the vicinity of DprE1 active site.

Vitek MS matrix-assisted laser desorption ionization-time of flight mass spectrometry for identifying respiratory bacterial pathogens: a fast and efficient method

Mass spectrometry has become a reference resource for identifying microorganisms in clinical microbiology services. One hundred and fifty one clinical isolates were selected from respiratory specimens routinely identified as Streptococcus pneumoniae (43), Haemophilus influenzae (64) and Moraxella catarrhalis (44). These identifications were compared with other phenotypical methods and mass spectrometry (MALDI-TOF-MS Vitek). Result discrepancies were assessed by 16S rRNA sequencing. Thirty-eight of the 43 strains of S. pneumoniae (86%) were identified as such using phenotypical methods and spectrometry. In 5 cases, MALDI-TOF identified 4 of them as Streptococcus pseudopneumoniae and 1 as S. mitis/oralis. Forty-eight of the 64 strains were identified as H. influenzae (75%) using biochemical identification systems and automated identification systems, whereas MALDI-TOF-MS Vitek identified 51 strains (79%) as such. Conventional methods and spectrometry identified all the 40 strains tested (100%) as M. catarrhalis. All strains with discrepant results were sequenced, and in all cases, the identification obtained by spectrometry was confirmed. The results obtained in this study show that mass spectrometry provides identification of these bacteria faster and in a more reliable way than those based on conventional phenotypical methods.

An Unusual Carbohydrate Conformation is Evident in Moraxella catarrhalis Oligosaccharides

Oligosaccharide structures derived from the lipooligosaccharide of M. catarrhalis show that the highly branched glucose-rich inner core of the oligosaccharide has an altered conformation compared to the most truncated tetra-glucose-Kdo lgt1/4Δ oligosaccharide structure. Addition of one residue each to the (1-4) and (1-6) chains to give the lgt2Δ oligosaccharide is the minimum requirement for this conformational change to occur. Extensive molecular modeling and NMR investigations have shown that the (1-3), (1-4), and (1-6) glycosidic linkages from the central α-d-Glcp have significantly altered conformational preferences between the two structures. For the lgt1/4Δ oligosaccharide the (1-3) and (1-4) linkage populates predominantly the syn minimum on the conformational free energy map and for the (1-6) linkage conformational flexibility is observed, which is supported by ¹H-NMR T1 measurements. For the lgt2Δ oligosaccharide the unusual “(1-4)anti-ψ(1-6)gg” conformation, which could be confirmed by long-range NOE signals, is a dominant conformation in which the oligosaccharide is very compact with the terminal α-d-GlcNAc residue folding back towards the center of the molecule leading to an extensive intra-molecular hydrophobic interaction between the terminal residues. Comparing effective H-H distances, which were calculated for conformational sub-ensembles, with the NOE distances revealed that typically multiple conformations could be present without significantly violating the measured NOE restraints. For lgt2Δ the presence of more than one conformation is supported by the NOE data.

uspA1 of Moraxella catarrhalis clinical isolates in Japan and its relationship with adherence to HEp-2 cells

The surface protein, UspA1, of Moraxella catarrhalis is involved in adherence to human epithelial cells. We examined the expression of uspA1, and adherence to HEp-2 cells of clinical isolates. The uspA1 gene was detected in 204 of 208 isolates. The 4 uspA1-negative isolates belonged to the 16S rRNA type II with an A to G substitution at nucleotide 445 of 16S rRNA. In 13 isolates of the 16S rRNA type II, transcription of uspA1 was decreased or absent. A relationship between the extent of uspA1 transcription and adherence to HEp-2 cells was found in 5 isolates of the type I. In contrast, the 16S rRNA type II strains still had considerable adherence to HEp-2 cells. The type I uspA1 gene was expressed in Escherichia coli JM109 and the transformants adhered to HEp-2 cells at rates about 7 times higher than the host strain. These data indicated that the uspA1 was virtually ubiquitous in clinical isolates of M. catarrhalis and was responsible for adherence to HEp-2 cells of 16S rRNA type I isolates. However, the data also suggested that adherence of 16S rRNA type II strains to HEp-2 cells was attributed to factor(s) other than UspA1.

Moraxella catarrhalis outer membrane protein CD elicits antibodies that inhibit CD binding to human mucin and enhance pulmonary clearance of M. catarrhalis in a mouse model

The outer membrane protein CD of Moraxella catarrhalis is considered to be a potential vaccine antigen against Moraxella infection. We purified the native CD from isolate O35E, administered it to mice, and detected considerable titers of anti-CD antibodies. Anti-CD sera were cross-reactive towards six different M. catarrhalis isolates and promoted bacterial clearance of O35E in a pulmonary challenge model. To circumvent the difficulty of generating large quantities of CD from M. catarrhalis for vaccine use, the CD gene from O35E was cloned into Escherichia coli, and the recombinant CD, expressed without a signal sequence or fusion tags, represented approximately 70% of the total E. coli proteins. The recombinant CD formed inclusion bodies that were solubilized with 6 M urea and then purified by ion-exchange chromatography, a procedure that produced soluble CD of high purity and yield. Mice immunized with the purified recombinant CD had significant titers of anti-CD antibodies that were cross-reactive towards 24 different M. catarrhalis isolates. Upon challenge, these mice showed enhanced bacterial clearance of both O35E and a heterologous M. catarrhalis isolate, TTA24. In an in vitro assay, antisera to either the native or the recombinant CD inhibited the binding activity of CD to human tracheobronchial mucin in a serum concentration-dependent manner, and the extent of inhibition appeared to correlate with the corresponding anti-CD antibody titer and whole-cell enzyme-linked immunosorbent assay titer. Our results demonstrate that the recombinant CD is a promising vaccine candidate for preventing Moraxella infection.

Moraxella catarrhalis strain O35E expresses two filamentous hemagglutinin-like proteins that mediate adherence to human epithelial cells

Two-partner secretion (TPS) systems are a family of proteins being rapidly identified and characterized in a growing number of gram-negative bacteria. TPS systems mediate the secretion of proteins, many involved in virulence traits such as hemolysis, adherence to epithelial cells, inhibition of bacterial growth, and immunomodulation of the host. A TPS system typically consists of a transporter located in the bacterial outer membrane (OM) which is responsible for the recognition and secretion of at least one large exoprotein. Two of the better-characterized TPS systems specify the Bordetella pertussis FHA and Haemophilus influenzae HMW1/HMW2 proteins. We identified three gene products of Moraxella catarrhalis strain O35E that resemble TPS proteins and designated them MhaC (transporter), MhaB1 (exoprotein), and MhaB2 (exoprotein). Western blot analysis using anti-MhaC, or antibodies reacting to both MhaB1 and MhaB2 (MhaB-reactive), revealed that these antigens are expressed in the OM of 63% of isolates tested. Mutations in the mhaC gene specifying the putative transporter of the M. catarrhalis wild-type strains O35E, O12E, and McGHS1 resulted in the absence of MhaB1/MhaB2 in the OM of mutants. These results are therefore consistent with the Mha proteins functioning as a TPS system. Furthermore, we discovered that these mhaC mutants exhibit markedly decreased binding to human epithelial cells relevant to pathogenesis by M. catarrhalis (Chang, HEp2, A549, and/or 16HBE14o(-)). Expression of O12E MhaC and MhaB1 in a nonadherent strain of Escherichia coli was found to increase the adherence of recombinant bacteria to HEp2 monolayers by sevenfold, thereby demonstrating that this M. catarrhalis TPS system directly mediates binding to human epithelial cells. The construction of isogenic mutants in the mhaB1 and mhaB2 genes of strain O35E also suggests that the MhaB proteins play distinct roles in M. catarrhalis adherence.

Characterization of the Moraxella catarrhalis opa-like protein, OlpA, reveals a phylogenetically conserved family of outer membrane proteins

Moraxella catarrhalis is a human-restricted pathogen that can cause respiratory tract infections. In this study, we identified a previously uncharacterized 24-kDa outer membrane protein with a high degree of similarity to Neisseria Opa protein adhesins, with a predicted beta-barrel structure consisting of eight antiparallel beta-sheets with four surface-exposed loops. In striking contrast to the antigenically variable Opa proteins, the M. catarrhalis Opa-like protein (OlpA) is highly conserved and constitutively expressed, with 25 of 27 strains corresponding to a single variant. Protease treatment of intact bacteria and isolation of outer membrane vesicles confirm that the protein is surface exposed yet does not bind host cellular receptors recognized by neisserial Opa proteins. Genome-based analyses indicate that OlpA and Opa derive from a conserved family of proteins shared by a broad array of gram-negative bacteria.

Binding of vitronectin by the Moraxella catarrhalis UspA2 protein interferes with late stages of the complement cascade

Many Moraxella catarrhalis strains are resistant to the bactericidal activity of normal human serum (NHS). The UspA2 protein of the serum-resistant strain O35E has previously been shown to be directly involved in conferring serum resistance on this strain. Testing of 11 additional serum-resistant M. catarrhalis wild-type isolates and their uspA1 and uspA2 mutants showed that the uspA1 mutants of all 11 strains were consistently serum resistant and that the uspA2 mutants of these same 11 strains were always serum sensitive. Analysis of complement deposition on four different serum-resistant M. catarrhalis strains and their serum-sensitive uspA2 mutants showed that, for three of these four strain sets, the wild-type and mutant strains bound similar amounts of early complement components. In contrast, there was a significant reduction in the amount of the polymerized C9 on the wild-type strains relative to that on the uspA2 mutants. These same three wild-type strains bound more vitronectin than did their uspA2 mutants. UspA2 proteins from these three strains, when expressed in Haemophilus influenzae, bound vitronectin and conferred serum resistance on this organism. Furthermore, vitronectin-depleted NHS exhibited bactericidal activity against these same three serum-resistant wild-type strains; addition of purified vitronectin to this serum restored serum resistance. In contrast, binding of the complement regulator C4b-binding protein by the M. catarrhalis strains used in this study was found to be highly variable and did not appear to correlate with the serum-resistant phenotype. These results indicate that binding of vitronectin by UspA2 is involved in the serum resistance of M. catarrhalis; this represents the first example of vitronectin-mediated serum resistance on a microbe.

Identification and characterization of a novel outer membrane protein (OMP J) of Moraxella catarrhalis that exists in two major forms

Moraxella catarrhalis is a common commensal of the human respiratory tract that has been associated with a number of disease states, including acute otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults. During studies to investigate the outer membrane proteins of this bacterium, two novel major proteins, of approximately 19 kDa and 16 kDa (named OMP J1 and OMP J2, respectively), were identified. Further analysis indicated that these two proteins possessed almost identical gene sequences, apart from two insertion/deletion events in predicted external loops present within the putative barrel-like structure of the proteins. The development of a PCR screening strategy found a 100% (96/96) incidence for the genes encoding the OMP J1 and OMP J2 proteins within a set of geographically diverse M. catarrhalis isolates, as well as a significant association of OMP J1/OMP J2 with both the genetic lineage and the complement resistance phenotype (Fisher's exact test; P < 0.01). Experiments using two DeltaompJ2 mutants (one complement resistant and the other complement sensitive) indicated that both were less easily cleared from the lungs of mice than were their isogenic wild-type counterparts, with a significant difference in bacterial clearance being observed for the complement-resistant isolate but not for its isogenic DeltaompJ2 mutant (unpaired Student's t test; P < 0.001 and P = 0.32). In this publication, we characterize a novel outer membrane protein of Moraxella catarrhalis which exists in two variant forms associated with particular genetic lineages, and both forms are suggested to contribute to bacterial clearance from the lungs.

Characterization of a novel porin protein from Moraxella catarrhalis and identification of an immunodominant surface loop

Moraxella catarrhalis is a gram-negative bacterium that is mainly responsible for respiratory tract infections. In this study we report a novel outer membrane protein (OMP), designated M35, with a molecular mass of 36.1 kDa. This protein was structurally homologous to classic gram-negative porins, such as OMP C from Escherichia coli and OMP K36 from Klebsiella pneumoniae, with a predicted structure of 8 surface loops and 16 antiparallel beta-sheets. The DNA sequences of the genes from 18 diverse clinical isolates showed that the gene was highly conserved (99.6 to 100% of nucleotides), with only one isolate (ID78LN266) having base variations that resulted in amino acid substitutions. Electrophoresis and analysis of recognition of the protein using mouse anti-M35 sera showed that M35 was expressed on the bacterial surface and constitutively expressed across M. catarrhalis isolates, with only ID78LN266 showing poor antibody recognition. Our results showed that the single amino acid mutation in loop 3 significantly affected antibody recognition, indicating that loop 3 appeared to contain an immunodominant B-cell epitope. The antibody specificity to loop 3 may be a potential mechanism for evasion of host immune responses targeted to M35, since loop 3 should theoretically orientate into the porin channel. Thus, M35 is a highly conserved, surface-expressed protein that is of significance for its potential functional role as an M. catarrhalis porin and is of interest as a vaccine candidate.

[Cross-reactions between the antigens of healthy pulmonary tissue and Moraxella catarrhalis]

The study of cross-reactions between healthy pulmonary tissue antigens and Moraxella catarrhalis with the use of SDS-electrophoresis and immunoblotting revealed that in the component of healthy pulmonary tissue with a mol. wt. of 40 kD epitopes existed to which antibodies were produced, capable of cross reaction with the components of M. catarrhalis with a mol. wt. of 35 kD and 70 kD. In addition, the presence of cross-reactions between cytokeratin-8, protein contained in healthy pulmonary tissue, and M. catarrhalis antigens was established.

Exploration ofMoraxella catarrhalisouter membrane proteins, CD and UspA, as new carriers for lipooligosaccharide-based conjugates

Moraxella catarrhalis outer membrane proteins, CD and ubiquitous surface protein A (UspA), were used as carriers for M. catarrhalis detoxified lipooligosaccharide (dLOS)-based conjugates. Our study was designed to investigate the feasibility of CD and UspA as protein carriers for dLOS-based conjugates and their possible synergic effects on protection from both anti-LOS and anti-CD or anti-UspA antibody responses. Female Balb/c mice were immunized subcutaneously three times with dLOS-CD or dLOS-UspA conjugate in Ribi adjuvant. Antisera elicited by the conjugates showed high titers of specific anti-LOS antibodies with complement-dependent bactericidal activity towards M. catarrhalis strain 25238. In a mouse aerosol challenge model, mice immunized with both conjugates showed a significant enhancement of the clearance of strain 25238 from lungs as compared with the control mice. Although both conjugates elicited reduced (relative to unconjugated CD or UspA) but significant levels of anti-CD or UspA antibodies, they did not show synergetic effects with anti-LOS antibodies on the bactericidal activity or the pulmonary bacterial clearance. Nevertheless, CD and UspA are safe and effective new carriers for dLOS-based or other potential carbohydrate-based conjugate vaccines to help thymus-independent carbohydrate antigens for production of anti-carbohydrate antibodies against target pathogens.

The immunoglobulin D-binding protein MID from Moraxella catarrhalis is also an adhesin

The Moraxella catarrhalis immunoglobulin D (IgD)-binding protein (MID) is a 200-kDa outer membrane protein displaying a unique and specific affinity for human IgD. MID is found in the majority of M. catarrhalis strains. In the present paper, we show that MID-expressing M. catarrhalis strains agglutinate human erythrocytes and bind to type II alveolar epithelial cells. In contrast, M. catarrhalis isolates with low MID expression levels and two mutants deficient in MID, but with readily detectable UspA1 expression, do not agglutinate erythrocytes and have a 50% lower adhesive capacity. To examine the adhesive part of MID, the protein was dissected into nine fragments covering the entire molecule. The truncated MID proteins were expressed in Escherichia coli, purified, and used for raising polyclonal antibodies in rabbits. Interestingly, by using recombinant fragments, we show that the hemagglutinating and adhesive part of MID is localized within the 150-amino-acid fragment MID(764-913). In addition, antibodies against full-length MID, MID(764-913), or a 30-amino-acid consensus sequence (MID(775-804)) inhibited adhesion to alveolar epithelial cells. Antibodies against UspA1, an outer membrane protein expressed in essentially all M. catarrhalis strains, also inhibited adhesion, suggesting that both MID and UspA1 are needed for optimal attachment to epithelial cells. Taken together, in addition to MID-dependent IgD binding, we have demonstrated that the outer membrane protein MID is a novel adhesin that would be a suitable target for a future vaccine against M. catarrhalis.

Method for reducing endotoxin in Moraxella catarrhalis UspA2 protein preparations

The UspA2 protein from the bacterium Moraxella catarrhalis is a potential vaccine candidate for preventing human diseases caused by this organism. Before a vaccine can be administered parentally, the level of endotoxin must be reduced as much as possible. However, in this case the endotoxin was very tightly complexed with the UspA2 protein and could not be dissociated with Triton X-100. It was found that it dissociated from the protein with the zwitterionic detergents Zwittergent 3-12 and Zwittergent 3-14. The endotoxin could then be separated from the protein by either ion-exchange or gel filtration chromatography. Using the limulus amoebocyte lysate assay for quantitation, the endotoxin was reduced approximately 20,000-fold. The removal of residual endotoxin from UspA2 preparations had no detrimental effect on the immunological properties of the protein. Mouse antisera raised against UspA2 prior to, and following endotoxin reduction exhibited comparable antibody and bactericidal titers against the tested strains. Further, mice immunized with both preparations, followed by pulmonary challenge with either a homologous or a heterologous isolate, exhibited comparable levels of clearance.

Structure and sequence analysis of Yersinia YadA and Moraxella UspAs reveal a novel class of adhesins

The non-fimbrial adhesins, YadA of enteropathogenic Yersinia species, and UspA1 and UspA2 of Moraxella catarrhalis, are established pathogenicity factors. In electron micrographs, both surface proteins appear as distinct 'lollipop'-shaped structures forming a novel type of surface projection on the outer membranes. These structures, amino acid sequence analysis of these molecules and yadA gene manipulation suggest a tripartite organization: an N-terminal oval head domain is followed by a putative coiled-coil rod and terminated by a C-terminal membrane anchor domain. In YadA, the head domain is involved in autoagglutination and binding to host cells and collagen. Analysis of the coiled-coil segment of YadA revealed unusual pentadecad repeats with a periodicity of 3.75, which differs significantly from the 3.5 periodicity found in the Moraxella UspAs and other canonical coiled coils. These findings predict that the surface projections are formed by oligomers containing right- (Yersinia) or left-handed (Moraxella) coiled coils. Strikingly, sequence comparison revealed that related proteins are found in many proteobacteria, both human pathogenic and environmental species, suggesting a common role in adaptation to specific ecological niches.

Moraxella catarrhalis: a review of an important human mucosal pathogen

Moraxella catarrhalis has again been recognized as a significant pathogen. The past decade has witnessed an increased amount of research and understanding of the pathogenesis of the organism. This review will summarize the research pertaining to the epidemiology and components of pathogenesis in M. catarrhalis.

The lipopolysaccharide of moraxella catarrhalis structural relationships and antigenic properties

Moraxella catarrhalis has recently been shown to be both widespread and pathogenic, in contrast to previous reports. Several factors have been suggested as virulence factors, lipopolysaccharide (LPS) being one. Recent studies have shown the LPS to be without the O-chain, i.e. the polysaccharide part, and to have specific structural features corresponding to each of the three serogroups, A, B and C. The structures resemble in many respects those present in other Gram-negative nonenteric bacteria, with a galabiosyl element as a prominent common denominator. The presence of such common structures suggests that the LPS of these bacteria might be a part of a mechanism of survival for bacteria colonizing the human host.

Tissue culture adherence and haemagglutination characteristics of Moraxella (Branhamella) catarrhalis

The haemagglutination and tissue culture adherence properties of 20 isolates of Moraxella catarrhalis obtained from the sputum of elderly patients with lower respiratory tract infections were compared with those of 20 isolates of M. catarrhalis obtained from the nasopharynx of elderly persons colonised by the organism. Eighty percent of isolates from the infected group as opposed to 5% of isolates from the colonised group haemagglutinated human erythrocytes (P < 0.001), indicating that the haemagglutinin might be a marker of pathogenicity for M. catarrhalis. There was a significant difference in the adherence to HEp-2 cells of isolates from the infected group in comparison to isolates from the colonised group (P = 0.03). Haemagglutination and tissue culture adherence properties were unrelated, indicating that separate adhesin systems are involved. The adherence of M. catarrhalis to HEp-2 cells was unaffected following pronase and trypsin treatment, however, sodium periodate pre-treatment of the bacteria significantly reduced the tissue culture adherence index, indicating that the adhesin by which the bacteria bind to HEp-2 cells may have a carbohydrate moiety. Transmission electron microscopy studies revealed that adherence of M. catarrhalis to HEp-2 cells was mediated by trypsin-resistant 'tack-/spicule-like' structures protruding from the surface of the bacteria.

Identification of sequences in human transferrin that bind to the bacterial receptor protein, transferrin-binding protein B

Alignment of amino-acid sequences from the N-terminal and C-terminal halves of transferrin-binding protein B revealed an underlying bilobed nature with several regions of identity. Based on this analysis, purified recombinant fusion proteins of maltose-binding protein (Mbp) with intact TbpB, its N-terminal half or C-terminal half from the human pathogens Neisseria meningitidis and Moraxella catarrhalis were produced. Solid-phase binding assays and affinity isolation assays demonstrated that the N-terminal and C-terminal halves of TbpB could bind independently to human transferrin (hTf). A solid-phase overlapping synthetic peptide library representing the amino-acid sequence of hTf was probed with soluble, labelled Mbp-TbpB fusions to localize TbpB-binding regions on hTf. An essentially identical series of peptides from domains within both lobes of hTf was recognized by intact TbpB from both organisms, demonstrating a conserved TbpB-hTf interaction. Both halves of TbpB from N. meningitidis bound the same series of peptides, which included peptides from equivalent regions on the two hTf lobes, indicating that TbpB interacts with each lobe of hTf in a similar manner. Mapping of the peptide-binding regions on a molecular model of hTf revealed a series of nearly adjacent surface regions that nearly encircled each lobe. Binding studies with chimeric hTf/bTf transferrins demonstrated that regions in the C-lobe of hTf were preferentially recognized by the N-terminal half of TbpB. Collectively, these results provide evidence that TbpB consists of two lobes, each with distinct yet homologous Tf-binding regions.

Transmission electron microscopy studies of Moraxella (Branhamella) catarrhalis

A trypsin-sensitive 200-kDa protein has been reported to be exclusively associated with haemagglutinating isolates of Moraxella (Branhamella) catarrhalis. Transmission electron microscopy studies revealed that haemagglutination by M. catarrhalis to both human and rabbit erythrocytes was mediated by a trypsin-sensitive outer fibrillar coat. This fibrillar layer was absent on non-haemagglutinating isolates examined. Immuno-electron microscopy, using a polyclonal antiserum containing antibodies to the 200-kDa protein as a probe, showed that the 200-kDa protein is present on the outer fibrillar layer of the bacterium. These findings suggest that the haemagglutinin of M. catarrhalis is a 200-kDa protein present on the outer fibrillar coat.

Discrimination between apo and iron-loaded forms of transferrin by transferrin binding protein B and its N-terminal subfragment

Many pathogens of the Pasteurellaceae and Neisseriaceae possess a surface receptor that binds transferrin (Tf) as an initial step in an iron acquisition process. This receptor is comprised of two proteins, transferrin binding protein A (TbpA) and transferrin binding protein B (TbpB). Since the ability to recognize the iron-loaded form of Tf preferentially would be a useful attribute of these receptors, we examined this property in a number of bacterial species. In solid-phase binding assays with isolated membranes, only the receptor from Moraxella catarrhalis was capable of preferentially binding iron-loaded Tf. In a competitive affinity isolation assay which enabled us to resolve TbpA and TbpB, TbpA from all tested species was shown to bind both apo and iron-loaded Tf. Under these assay conditions TbpB from M. catarrhalis, Haemophilus somnus and Pasteurella haemolytica discriminated between apo and holo Tf, whereas TbpB from Neisseria meningitidis showed no discrimination. The ability of TbpB from N. meningitidis to bind iron-saturated hTf preferentially became evident in a TbpA- background or by using recombinant TbpB. In binding assays with recombinant fusion proteins, both intact TbpB and the N-terminal half of TbpB from all the tested species preferentially bound Fe-loaded Tf, indicating that this may be a conserved mechanism by which these organisms optimize their ability to acquire iron.

Monoclonal antibodies to the epitope alpha-Gal-(1-4)-beta-Gal-(1- of Moraxella catarrhalis LPS react with a similar epitope in type IV pili of Neisseria meningitidis

Murine monoclonal antibodies (MAbs) against the A, B and C LPS serotypes of M. catarrhalis were generated and their binding specificity was examined in an enzyme-linked immunosorbent assay (ELISA). Two broadly cross-reactive monoclonal antibodies (MCA1 and MCC2) against the outer core region of LPS were further characterized. A panel of synthetic glycoproteins and glycolipids was used to determine the binding specificity of the MAbs. MCA1 and MCC2 bound specifically to alpha-Gal-(1-4)-beta-Gal of galabiose and globotriose glycoconjugates. The reactivity of the MAbs with galabiose was higher than that with globotriose. The MAbs could recognize the alpha-Gal-(1-4)-beta-Gal epitope only when it was in a terminal position. MCA1 was further shown to react with a similar epitope in the glycosylated type IV pili of N. meningitidis, which has been shown to contain a 1-4 linked digalactose at the terminal part of the saccharide present in the pili. MCA1 could efficiently recognize this epitope indicating that it was exposed on the surface of the pili.

Biochemical and immunological properties of lactoferrin binding proteins from Moraxella (Branhamella) catarrhalis

The Neisseriaceae can acquire iron (Fe) from lactoferrin (Lf) using host-Lf receptors on the bacterial surface. The binding proteins that are proposed to constitute the receptor have been identified by isolation with immobilized Lf. Using CopB-specific monoclonal antibodies and isogenic CopB mutants, we demonstrate that the 84 kDa protein isolated with immobilized human Lf from Moraxella catarrhalis using low stringency conditions is CopB, an 84 kDa membrane-spanning protein with similarities to other TonB-dependent outer membrane proteins. Affinity isolation of Lf receptors from a variety of M. catarrhalis strains using high stringency conditions revealed a 95 kDa protein migrating slightly faster than LbpA on SDS-PAGE in some strains. Convalescent human antisera from patients infected with M. catarrhalis reacted specifically with this protein, but not LbpA. Proteolysis experiments demonstrated that, unlike LbpA, it was rapidly degraded. The 95 kDa protein, but not LbpA, binds labelled Lf after SDS-PAGE and electroblotting, suggesting the 95 kDa protein is LbpB, the homologue of TbpB. This protein comigrates with LbpA in most strains, which may explain why it had not been previously identified.

Phylogeny of the family Moraxellaceae by 16S rDNA sequence analysis, with special emphasis on differentiation of Moraxella species

Thirty-three strains previously classified into 11 species in the bacterial family Moraxellaceae were subjected to phylogenetic analysis based on 16S rRNA sequences. The family Moraxellaceae formed a distinct clade consisting of four phylogenetic groups as judged from branch lengths, bootstrap values and signature nucleotides. Group I contained the classical moraxellae and strains of the coccal moraxellae, previously known as Branhamella, with 16S rRNA similarity of > or = 95%. A further division of group I into five tentative clusters is discussed. Group II consisted of two strains representing Moraxella atlantae and Moraxella osloensis. These strains were only distantly related to each other (93.4%) and also to the other members of the Moraxellaceae (< or = 93%). Therefore, reasons for reclassification of these species into separate and new genera are discussed. Group III harboured strains of the genus Psychrobacter and strain 752/52 of [Moraxella] phenylpyruvica. This strain of [M.] phenylpyruvica formed an early branch from the group III line of descent. Interestingly, a distant relationship was found between Psychrobacter phenylpyruvicus strain ATCC 23333T (formerly classified as [M.] phenylpyruvica) and [M.] phenylpyruvica strain 752/52, exhibiting less than 96% nucleotide similarity between their 16S rRNA sequences. The establishment of a new genus for [M.] phenylpyruvica strain 752/52 is therefore suggested. Group IV contained only two strains of the genus Acinetobacter. Strategies for the development of diagnostic probes and distinctive sequences for 16S rRNA-based species-specific assays within group I are suggested. Although these findings add to the classificatory placements within the Moraxellaceae, analysis of a more comprehensive selection of strains is still needed to obtain a complete classification system within this family.

Characterisation of an outer membrane protein of Moraxella catarrhalis

To elucidate potential vaccine antigens, Moraxella catarrhalis outer membrane proteins (OMPs) were studied. We have previously shown an OMP to be a target for human IgG and have now further characterised this OMP which appears to have a molecular mass of 84 kDa and to be distinct from the 81-kDa OMP, CopB. Human transferrin was shown to bind the 84-kDa OMP alone. N-terminal sequencing of this OMP and purified M. catarrhalis transferrin binding protein B (TbpB) revealed homology both with each other and with the TbpB of Haemophilus influenzae and Neisseria meningitidis. Adsorption of human anti-serum with purified TbpB from two M. catarrhalis strains abolished or reduced binding of IgG to the 84-kDa OMP from three M. catarrhalis isolates. IgG binding to CopB was unaffected. It is clear that the 84-kDa OMP is distinct from CopB and is a likely homologue of TbpB.

The structures of oligosaccharides isolated from the lipopolysaccharide of Moraxella catarrhalis serotype B, strain CCUG 3292

The oligosaccharides from the lipopolysaccharides of Moraxella catarrhalis serotype B, strain CCUG 3292, were isolated after mild acid hydrolysis and separated by high-performance anion-exchange chromatography. The structures of the oligosaccharides were established by fast atom bombardment mass spectrometry and nuclear magnetic resonance spectroscopy. It is concluded that the oligosaccharides comprise a mixture of mainly a nona- and a deca-saccharide. [formula: see text] Smaller amounts of undeca-saccharides and of truncated forms, namely, hexa-, hepta-, and octa-saccharides, were also detected.

Serum antibody response to outer membrane proteins of Moraxella (Branhamella) catarrhalis in patients with bronchopulmonary infection

A Western blot (immunoblot) method for detecting antibodies against outer membrane protein (OMP) epitopes of Moraxella (Branhamella) catarrhalis was evaluated. Paired serum samples from patients suspected of M. catarrhalis (n = 38) and non-M. catarrhalis (n = 25) bronchopulmonary infection were examined for the presence of antibodies of the immunoglobulin M (IgM), IgG, and IgA classes to OMPs from M. catarrhalis by a gel electrophoresis-immunoperoxidase technique (Western blotting); sera from 40 healthy adult blood donors were also included. A significantly (P = 0.004) more frequent occurrence of IgM-class antibodies and/or an increase in the number of IgG-class antibodies against different M. catarrhalis OMPs from acute- to convalescent-phase serum samples was found for patients with M. catarrhalis (79%) than for patients without M. catarrhalis (40%). IgM-class antibodies against OMPs of M. catarrhalis were found in acute- and/or convalescent-phase serum samples form 58% of patients with M. catarrhalis and 32% of patients without M. catarrhalis. Fifty percent of patients with M. catarrhalis and 16% of patients without M. catarrhalis had, from acute- to convalescent-phase serum samples, an increased number of IgG-class antibodies directed against different OMPs. A total of 34% of patients with M. catarrhalis and 4% of patients without M. catarrhalis had, from acute- to convalescent-phase serum samples, an increased number of IgA-class antibodies directed against different OMPs. The present study indicates that M. catarrhalis is one of the bacteria involved in acute exacerbations of chronic bronchitis.

Separation and characterization of O-deacylated lipooligosaccharides and glycans derived from Moraxella catarrhalis using capillary electrophoresis-electrospray mass spectrometry and tandem mass spectrometry

Electrophoretic methods have been developed for the analysis of complex carbohydrates derived from lipooligosaccharides (LOS) of Moraxella catarrhalis using capillary electrophoresis coupled to electrospray mass spectrometry (CE-ESMS). Separation of lipooligosaccharides (LOS) arising from mild hydrazinolysis of the intact lipopolysaccharides (LPS) was achieved using aqueous ammonium formate, and enabled identification of sites of heterogeneity (phosphates, phosphoethanolamine, and pendant acyl groups) on either the lipid A or the core oligosaccharide. More complex mixtures of carbohydrates obtained from the complete deacylation and dephosphorylation of LOS were amendable to electrophoretic conditions using both anionic and cationic separation. In particular, electrophoretic conditions were developed which permitted resolution of closely related oligosaccharides according to the number of carbohydrate residues appended to the core structure. Structural characterization of carbohydrates and LOS released from the hydrazinolysis and acid hydrolysis treatment of the intact LPS was achieved using tandem mass spectrometry (MS-MS) for samples introduced by direct flow injection. Taken together, the combination of CE-ESI-MS and MS-MS analyses provided valuable information on the heterogeneity of the LOS population in which a significant level of variability was found mostly in the lipid A portion.

Synthesis of 2-(4-aminophenyl)ethyl 3-deoxy-5-O-(3,4,6-tri-O-beta-D- glucopyranosyl-alpha-D-glucopyranosyl)-alpha-D-manno-oct-2-ulopyrano sid onic acid, a highly branched pentasaccharide corresponding to structures found in lipopolysaccharides from Moraxella catarrhalis

Syntheses of the pentasaccharide 2-(4-aminophenyl)ethyl 3-deoxy-5-O-(3,4,6- tri-O-beta-D-glucopyranosyl-alpha-D-glucopyranosyl)-alpha-D-manno-oct-2- ulopyranosidonic acid and of the tetrasaccharide 3,4,6-tri-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside, both as its methyl and 2-(4-trifluoro-acetamidophenyl)ethyl glycoside, are described. These oligosaccharides correspond to structures found in the lipopolysaccharide of Moraxella catarrhalis and were needed for biological experiments aimed at producing antibodies against the bacteria. The best way to introduce the glucopyranosyl groups into the 3-, 4-, and 6-positions of the branched target compounds was found to be a one-step reaction using a 3,4,6-triol as acceptor and 2,3,4,6-tetra-O-benzoyl-D-glucopyranosyl bromide as donor in a silver trifluoromethanesulfonate-promoted coupling. The spacer arm, necessary for the formation of immunoactive glycoconjugates, was introduced into the glucose moiety via a dimethyl(methylthio)sulfonium trifluoromethanesulfonate-promoted reaction using the ethyl thioglucoside as donor, whereas for Kdo, the acetylated glycal derivative, methyl 4,5,7,8-tetra-O-acetyl-2,6-anhydro-3-deoxy-D-manno-oct-2-enonate, was used as donor and phenylselenyl trifluoromethanesulfonate as a stereocontrolling promoter.

Biochemical analysis of lactoferrin receptors in the Neisseriaceae: identification of a second bacterial lactoferrin receptor protein

Bacterial transferrin receptors that have been described in the families Pasteurellaceae and Neisseriaceae are composed of two receptor proteins, transferrin binding proteins 1 and 2 (Tbp1 and Tbp2). In contrast, bacterial lactoferrin receptors have only been described for human pathogens in the family Neisseriaceae, and were believed to consist of a single protein, Lbp1, which is highly homologous to Tbp1. We describe a modified affinity isolation procedure that facilities isolation of a second lactoferrin receptor protein Lbp2 (a presumptive Tbp2 homologue) from Neisseria meningitidis, Moraxella catarrhalis and Moraxella bovis using immobilized lactoferrin. Antiserum specific for either the M. catarrhalis Tbp1+2 molecules, the M. catarrhalis Lbp1 molecule, or for a commercial preparation of human lactoferrin did not react on western blots with the same organisms' affinity purified Lbp2. In addition, the M. catarrhalis Lbp2 could be isolated in a functional form without contaminating Lbp1 or Tbp1+2. We also demonstrate that the bovine pathogen, M. bovis, produces functional transferrin and lactoferrin receptors specific for the bovine forms of these glycoproteins. A putative lbpB gene, recently speculated to reside immediately upstream of the N. meningitidis Lbp1 structural gene, lbpA, likely encodes the newly isolated Lbp2 protein from this bacterial species.

Outer membrane protein CD of Branhamella catarrhalis: sequence conservation in strains recovered from the human respiratory tract

Branhamella catarrhalis causes lower respiratory tract infections in patients with chronic obstructive pulmonary disease. The outer membrane protein CD (OMP-CD) of B. catarrhalis is a major, heat-modifiable OMP. The goals of this study are to characterize the degree of conservation of OMP-CD among strains and to investigate if OMP-CD maintains its homogeneity under the effect of host immune selective pressure. Isolates of B. catarrhalis were collected prospectively from patients with bronchiectasis and chronic bronchitis. We studied the OMP-CD gene by analysis of PCR restriction fragment length polymorphisms (PCR-RFLP) and further determined DNA sequence of the CD gene of eight selected isolates. Five patterns of PCR-RFLP of the OMP-CD gene were observed among all isolates when the gene was digested with Sau3AI. The sequence analysis revealed a high degree of homogeneity in OMP-CD among strains of B. catarrhalis. Three regions of OMP-CD with minimal sequence heterogeneity were identified. The sequences of the OMP-CD gene of isolates collected from patients colonized with the same strain for up to 6 months was identical. These observations establish that the OMP-CD of B. catarrhalis recovered from clinical isolates is highly conserved among strains.

Structural studies of the O-antigen oligosaccharides from two strains of Moraxella catarrhalis serotype C

The oligosaccharide parts from Moraxella (Branhamella) catarrhalis serotype C lipooligosaccharides were isolated by mild acid hydrolysis followed by gel permeation chromatography. Four different oligosaccharides could be identified from strain RS26 and two from strain RS10. The structures of the O-oligosaccharides were established by methylation analyses, mass spectrometry, and NMR spectroscopy. It is concluded that the oligosaccharide O-antigens from RS26 are a mixture of octa-, deca-, and undeca-saccharides, and most likely a heptasaccharide. Strain RS10 contains the deca- and the undeca-saccharide only. The structures for the oligosaccharides are shown below. [formula: see text] OS(7) [formula: see text] OS(8) [formula: see text] OS(10) [formula: see text] OS(11) Methylation analysis of the intact lipooligosaccharides showed that two Kdo residues were present, one terminal and one 4,5-substituted residue. It also showed that they consisted of a lipid A portion with 6-substituted glucosamine residues.

252Cf-plasma desorption mass spectrometry analysis of lipids A obtained by an elimination reaction under mild conditions

Lipids A are the hydrophobic domains of bacterial endotoxic lipopolysaccharides. Since they are responsible for most of the biological activities (both pathogenic and beneficial) of endotoxins, the characterization of their structure is crucial to the understanding of their mode of action. However, the inadequacy of existing methods for preparing certain lipids A has prompted us to devise a new, mild procedure which gives intact products. Use was made of the special features of 252Cf-plasma desorption mass spectrometry for forming molecular ions from these species and giving qualitative and quantitative information from the primary mass spectrum.

Structural studies of the O-polysaccharide from the lipopolysaccharide of Moraxella (Branhamella) catarrhalis serotype A (strain ATCC 25238)

The polysaccharide of the Moraxella (Branhamella) catarrhalis serotype A lipopolysaccharide was prepared by mild acid hydrolysis followed by gel permeation chromatography. The structure was established by methylation analysis, mass spectrometry, and NMR spectroscopy. It is concluded that the O-antigenic polysaccharide has the following structure. [formula see text] Methylation analysis of the intact lipopolysaccharide showed that the lipid A portion consisted of 6-substituted glucosamine residues. Methylation followed by methanolysis showed that two Kdo residues were present, one terminal and one 4,5-substituted residue. A terminal Kdo thus substitutes the branch-point Kdo in the 4-position.

Purification and characterization of a high-molecular-weight outer membrane protein of Moraxella (Branhamella) catarrhalis

Moraxella (Branhamella) catarrhalis is an important bacterial cause of otitis media in children and lower respiratory tract infections in adults. In this study, we describe the presence of a novel high-molecular-weight outer membrane protein (HMW-OMP). This protein varies from 350 to 720 kDa in apparent molecular mass among strains by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein was detected on SDS-PAGE in 13 of 14 strains tested. We developed a monoclonal antibody and polyclonal antisera to this protein. In immunoblot assays, the protein was present in all 14 strains tested. The immunoblot assays suggest that the protein has at least one epitope that is conserved among strains. A purification method using anion-exchange chromatography is described. Treatment of outer membrane preparations and purified protein by heat and reducing agents did not change the apparent molecular mass of the HMW-OMP. Formic acid treatment of outer membrane preparations and purified HMW-OMP produced a single band with an apparent molecular mass of 120 to 140 kDa. We postulate that this may be the monomer of an oligomeric protein. The HMW-OMP, which varies in molecular mass among strains and is antigenically conserved, will be studied further to determine its role in the human immune response and may be useful as a marker in studying strain acquisition in patients.

Characterization of the lipopolysaccharide of Moraxella catarrhalis. Structural analysis of the lipid A from M. catarrhalis serotype A lipopolysaccharide

The lipopolysaccharide of Moraxella catarrhalis serotype A (ATCC 25238) was found to consist of a short-chain oligosaccharide attached to a lipid A moiety. Composition and NMR analyses showed the oligosaccharide component in O-deacylated LPS to be composed of D-glucose, D-galactose, 2-acetamido-2-deoxy-D-glucose and 3-deoxy-D-manno-octulosonic acid in the molar ratio of 5:2:1:2. In addition, the lipid A region contained phosphate, D-glucosamine, 3-hydroxydodecanoic acid, dodecanoic acid and decanoic acid. The lipid A was examined in detail by high-field NMR spectroscopy and mass spectrometry. It was found to consist of a beta-1,6-D-glucosamine disaccharide backbone esterified at C4' by a phosphomonoester and glycosidically at C1 by diphosphoethanolamine or phosphomonoester. The amide group of the reducing and nonreducing glucosamine residues were acylated by 3-dodecanoyloxydodecanoic acid and 3-decanoyl-oxydodecanoic acid, respectively. The hydroxyl group at C3 and C3' were acylated by 3-decanoyl-oxydodecanoic acid and 3-hydroxydodecanoic acid respectively, while the hydroxyl groups at C4 and C6' were unsubstituted.

Characterisation of hospital isolates of Moraxella (Branhamella) catarrhalis by SDS-PAGE of whole-cell proteins, immunoblotting and restriction-endonuclease analysis

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins (WCP), immunoblot analysis and DNA restriction-endonuclease analysis (REA) were applied as potential typing methods to 31 clinically significant strains of Moraxella (Branhamella) catarrhalis, five of which came from a suspected outbreak of nosocomial infection in a respiratory-diseases ward. Twelve of 31 isolates were placed in four groups, each of which contained strains indistinguishable by the three typing techniques used. Each of a further two groups contained two strains, and they were similar by at least one technique; the remaining 15 strains were unique by all three methods. Four of five strains from the suspected outbreak were indistinguishable by SDS-PAGE of WCP, immunoblotting and REA. Results show that SDS-PAGE of WCP, immunoblotting and REA are suitable techniques for characterising M. catarrhalis and that there is a considerable degree of strain heterogeneity. Nosocomial infection with M. catarrhalis may be relatively common and further epidemiological studies with a combination of typing techniques are indicated.

[Biochemical analysis of lipopolysaccharides from respiratory pathogenic Branhamella catarrhalis strains and the role of anti-LPS antibodies in Branhamella respiratory infections]

We characterized lipopolysaccharides (LPSs) from respiratory pathogenic Branhamella catarrhalis (BC) strains, and evaluated the protective property of anti-BC LPS antibody in BC respiratory infections. LPSs from four strains of BC were lipooligosaccharide having no O-side chain and a M(r) of 3 KDa, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). All of them produced different patterns, showing two to four bands on SDS-PAGE. We found high level of anti-BC IgG antibody in convalescent sera from a patient with BC respiratory tract infection by ELISA. This IgG antibody recognized BC LPSs on Western blots. Two respiratory pathogens of BC (strains; 87-122, 88-23) were tested in a bactericidal assay employing a convalescent sera. 87-122 strain was susceptible to antibody-dependent, complement-mediated killing, while 88-23 strain was resistant. The killing of 87-122 strain was inhibited by addition of the homologous BC LPS to the convalescent sera in a dose-dependent manner. These data support that anti-BC LPS antibody may mediate complement-lysis of some strains of BC, and play a protective role in BC respiratory infections.

Pulmonary clearance of Moraxella catarrhalis in an animal model

The virulence mechanisms of Moraxella catarrhalis that are involved in producing pulmonary infection are unknown. A well-characterized murine model was used to study the pulmonary clearance of M. catarrhalis and analyze the histopathologic changes and the role of phagocytic cells in the infected lungs. Ten strains of M. catarrhalis from various isolation sites were evaluated for their ability to resist pulmonary clearance. The rates of clearance of these strains, based on the percentage of the original inoculum remaining at 6 h after challenge, varied considerably. Histopathologic examination of lungs infected with 2 strains that exhibited very different clearance rates revealed similar pathologic responses. Analysis of the phagocytic cell response to these 2 strains revealed significant alveolar recruitment of granulocytes at 3, 6, and 24 h after bacterial challenge. However, granulocyte recruitment in response to strain B22, which was cleared readily, was significantly greater than to strain 035E, which resisted pulmonary clearance. This model system should facilitate investigation of the molecular basis of the interaction between M. catarrhalis and the lower respiratory tract.

Use of molecular methods to characterize Moraxella catarrhalis strains in a suspected outbreak of nosocomial infection

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of whole cell protein, immunoblotting with normal human serum and restriction endonuclease analysis using Taq I enzyme were applied to 38 clinically significant isolates of Moraxella (Branhamella) catarrhalis obtained during a suspected outbreak of nosocomial infection. Each of 18 strains had individual profiles by at least two of the three methods (unique strains). The remaining 20 strains were assigned to five groups (A-E) on the basis of similarity by at least two of the three methods. Isolates within groups A, D and E were homologous by all three methods. Immunoblot groups B and C had two distinct whole cell protein profiles (B1 and B2) but indistinguishable restriction endonuclease profiles (group B/C). This emphasizes the need to use more than one technique in characterizing strains from suspected outbreaks of nosocomial infection. Grouped strains were more likely to originate from the same hospital ward than unique strains and were associated with a significantly longer median time from patient admission to strain isolation (14 versus 3.5 days, p less than 0.005). Furthermore, the beta-lactamase activity was homologous within the groups. The results suggest that nosocomial infection involving several distinct Moraxella catarrhalis strains persisted over a period of months, involving at least 20 patients on three different wards. Such infection is probably common in wards harbouring suitably predisposed patients. The mode of transmission remains to be elucidated, but the above three techniques possess sufficient reproducibility and discriminatory ability to constitute suitable investigative tools.