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Burkholderia mallei is a highly pathogenic bacterium that causes the fatal zoonosis glanders. The organism specifies multiple membrane proteins, which represent prime targets for the development of countermeasures given their location at the host-pathogen interface. We investigated one of these proteins, Pal, and discovered that it is involved in the ability of B. mallei to resist complement-mediated killing and replicate inside host cells in vitro, is expressed in vivo and induces antibodies during the course of infection, and contributes to virulence in a mouse model of aerosol infection. A mutant in the pal gene of the B. mallei wild-type strain ATCC 23344 was found to be especially attenuated, as BALB/c mice challenged with the equivalent of 5,350 LD50 completely cleared infection. Based on these findings, we tested the hypothesis that a vaccine containing the Pal protein elicits protective immunity against aerosol challenge. To achieve this, the pal gene was cloned in the vaccine vector Parainfluenza Virus 5 (PIV5) and mice immunized with the virus were infected with a lethal dose of B. mallei. These experiments revealed that a single dose of PIV5 expressing Pal provided 80% survival over a period of 40 days post-challenge. In contrast, only 10% of mice vaccinated with a PIV5 control virus construct survived infection. Taken together, our data establish that the Peptidoglycan-associated lipoprotein Pal is a critical virulence determinant of B. mallei and effective target for developing a glanders vaccine.

Conserved Moraxella catarrhalis (Mcat) proteins, oligopeptide permease (Opp)A, hemagglutinin (Hag), outer membrane protein (OMP) CD, Pilin A clade 2 (PilA2), and Moraxella surface protein (Msp) 22 ...

Background Moraxella catarrhalis ( Mcat ) is a frequent pathogen of acute otitis media (AOM) in young children. Here we prospectively assessed naturally-induced serum antibodies to four Mcat vaccine candidate proteins in stringently defined otitis prone (sOP) and non-otitis prone (NOP) children age 6–36 months old following nasopharyngeal (NP) colonization, at onset of AOM and convalescence from AOM. Methods Serum IgG and IgM antibody against recombinant Mcat proteins, oligopeptide permease A (OppA), outer membrane protein (OMP) CD, hemagglutinin (Hag), and PilA clade 2 (PilA2), were quantitated by ELISA. Results During NP colonization by Mcat all four antigens were immunogenic in both sOP and NOP children. However, sOP children had lower antibody responses than NOP children across age 6–36 months, similar to our findings for protein vaccine candidates of Streptococcus pneumoniae ( Spn ) and Nontypeable Haemophilus influenzae (NTHi). sOP children displayed a later and lower peak of antibody rise than NOP children for all four antigens during NP colonization of Mcat . The age-dependent increase of antibody ranked as OppA > Hag5-9 > OMP CD > PilA2 in both sOP and NOP children. Lower serum antibody levels to the Mcat antigens were measured in sOP compared to NOP children at the onset of AOM. We did not find a consistent significant increase of antibody at the convalescence phase after an AOM event. Conclusions sOP children is a highly vulnerable population that mount lower serum antibody responses to Mcat candidate vaccine proteins compared to NOP children during asymptomatic NP carriage and at onset of AOM.

BACKGROUND: Persistence of bacterial pathogens in the airways has profound consequences on the course and pathogenesis of chronic obstructive pulmonary disease (COPD). Patients with COPD continuously acquire and clear strains of Moraxella catarrhalis, a major pathogen in COPD. Some strains are cleared quickly and some persist for months to years. The mechanism of the variability in duration of persistence is unknown. METHODS: Guided by genome sequences of selected strains, we studied the expression of Hag/MID, hag/mid gene sequences, adherence to human cells, and autoaggregation in longitudinally collected strains of M. catarrhalis from adults with COPD. RESULTS: Twenty-eight of 30 cleared strains of M. catarrhalis expressed Hag/MID whereas 17 of 30 persistent strains expressed Hag/MID upon acquisition by patients. All persistent strains ceased expression of Hag/MID during persistence. Expression of Hag/MID in human airways was regulated by slipped-strand mispairing. Virulence-associated phenotypes (adherence to human respiratory epithelial cells and autoaggregation) paralleled Hag/MID expression in airway isolates. CONCLUSIONS: Most strains of M. catarrhalis express Hag/MID upon acquisition by adults with COPD and all persistent strains shut off expression during persistence. These observations suggest that Hag/MID is important for initial colonization by M. catarrhalis and that cessation of expression facilitates persistence in COPD airways.

Background: Burkholderia mallei and Burkholderia pseudomallei are the causative agents of glanders and melioidosis, respectively. There is no vaccine to protect against these highly-pathogenic and intrinsically antibiotic-resistant bacteria, and there is concern regarding their use as biological warfare agents. For these reasons, B. mallei and B. pseudomallei are classified as Tier 1 organisms by the U.S. Federal Select Agent Program and the availability of effective countermeasures represents a critical unmet need. Methods: Vaccines (subunit and vectored) containing the surface-exposed passenger domain of the conserved Burkholderia autotransporter protein BatA were administered to BALB/c mice and the vaccinated animals were challenged with lethal doses of wild-type B. mallei and B. pseudomallei strains via the aerosol route. Mice were monitored for signs of illness for a period of up to 40 days post-challenge and tissues from surviving animals were analyzed for bacterial burden at study end-points. Results: A single dose of recombinant Parainfluenza Virus 5 (PIV5) expressing BatA provided 74% and 60% survival in mice infected with B. mallei and B. pseudomallei, respectively. Vaccination with PIV5-BatA also resulted in complete bacterial clearance from the lungs and spleen of 78% and 44% of animals surviving lethal challenge with B. pseudomallei, respectively. In contrast, all control animals vaccinated with a PIV5 construct expressing an irrelevant antigen and infected with B. pseudomallei were colonized in those tissues. Conclusion: Our study indicates that the autotransporter BatA is a valuable target for developing countermeasures against B. mallei and B. pseudomallei and demonstrates the utility of the PIV5 viral vaccine delivery platform to elicit cross-protective immunity against the organisms. Keywords: Glanders, Melioidosis, Lethal aerosol challenge, PIV5 vaccine vector, Tier 1 select agent, Autotransporter protective antigen

Background Burkholderia mallei (Bm) is a facultative intracellular bacterial pathogen causing highly-fatal glanders in solipeds and humans. The ability of Bm to thrive intracellularly is thought to be related to exploitation of host immune response-related genes and pathways. Relatively little is known of the molecular strategies employed by this pathogen to modulate these pathways and evade intracellular killing. This manuscript seeks to fill gaps in the understanding of the interface between Bm and innate immunity by examining gene expression changes during infection of host monocytes. Methods The transcriptome of Bm-infected human Mono Mac-6 (MM6) monocytes was profiled on Affymetrix Human Transcriptome GeneChips 2.0. Gene expression changes in Bm-infected monocytes were compared to those of Burkholderia thailandensis (Bt)-infected monocytes and to uninfected monocytes. The resulting dataset was normalized using Robust Multichip Average and subjected to statistical analyses employing a univariate F test with a random variance model. Differentially expressed genes significant at p

There is no licensed vaccine for Moraxella catarrhalis (Mcat), which is a prominent bacterium causing acute otitis media (AOM) in children and lower respiratory tract infections in adults. Nasopharyngeal (NP) colonization caused by respiratory bacteria results in natural immunization of the host. To identify Mcat antigens as vaccine candidates, we evaluated the development of naturally induced antibodies to 5 Mcat surface proteins in children 6-30 months of age during Mcat NP colonization and AOM.Human serum IgG against the recombinant Mcat proteins, outer membrane protein (OMP) CD, oligopeptide permease (Opp)A, hemagglutinin (Hag), Moraxella surface protein (Msp)22, and PilA clade 2 (PilA2) was quantitated by using an ELISA assay.There were 223 Mcat NP colonization episodes documented in 111 (60%) of 184 children in the study. Thirty five Mcat AOM episodes occurred in 30 (16%) of 184 children. All 5 Mcat candidate vaccine antigens evaluated stimulated a significant rise in serum IgG levles over time from 6 to 36 months of age (P0.001), with a rank order as follows: Msp22=OppAOMP CD=Hag=PilA2. Children with no detectable Mcat NP colonization showed a higher serum IgG level against OppA, Hag, and Msp22 compared to those with Mcat NP colonization (P0.05). Individual data showed that some children responded to AOM with an antibody increase to one or more of the studied Mcat proteins but some children failed to respond.Serum antibody to Mcat candidate vaccine proteins OMP CD, OppA, Msp22, Hag, and PilA2 increased with age in naturally immunized children age 6-30 months following Mcat NP colonization and AOM. High antibody levels against OppA, Msp22, and Hag correlated with reduced carriage. The results support further investigation of these vaccine candidates in protecting against Mcat colonization and infection.

Burkholderia mallei causes the highly contagious and debilitating zoonosis glanders, which infects via inhalation or percutaneous inoculation and often culminates in life-threatening pneumonia and sepsis. In humans, glanders is difficult to diagnose and requires prolonged antibiotic therapy with low success rates. No vaccine exists to protect against B. mallei, and there is concern regarding its use as a bioweapon. The authors previously identified the protein BpaB as a potential target for devising therapies due to its role in adherence to host cells and the formation of biofilms in vitro and its contribution to pathogenicity in a mouse model of glanders. In the present study, the authors developed an immunostaining approach to probe tissues of experimentally infected animals and demonstrated that BpaB is produced exclusively in vivo by wild-type B. mallei in target organs from mice and marmosets. They detected the expression of BpaB by B. mallei both extracellularly and within macrophages, neutrophils, and epithelial cells in respiratory tissues (7/10 marmoset; 2/2 mouse). The authors also noted the intracellular expression of BpaB by B. mallei in macrophages in the regional lymph nodes of mice (2/2 tissues) and MALT of marmosets (4/5 tissues). It is interesting that B. mallei bacteria infecting distal organs did not express BpaB (2/2 mice; 3/3 marmosets), suggesting that the protein is not necessary for bacterial fitness in these anatomic locations. These findings underscore the value of BpaB as a target for developing medical countermeasures and provide insight into its role in pathogenesis.

Burkholderia mallei , a facultative intracellular bacterium and tier 1 biothreat, causes the fatal zoonotic disease glanders. The organism possesses multiple genes encoding autotransporter proteins, which represent important virulence factors and targets for developing countermeasures in pathogenic Gram-negative bacteria. In the present study, we investigated one of these autotransporters, BatA, and demonstrate that it displays lipolytic activity, aids in intracellular survival, is expressed in vivo , elicits production of antibodies during infection, and contributes to pathogenicity in a mouse aerosol challenge model. A mutation in the batA gene of wild-type strain ATCC 23344 was found to be particularly attenuating, as BALB/c mice infected with the equivalent of 80 median lethal doses cleared the organism. This finding prompted us to test the hypothesis that vaccination with the batA mutant strain elicits protective immunity against subsequent infection with wild-type bacteria. We discovered that not only does vaccination provide high levels of protection against lethal aerosol challenge with B. mallei ATCC 23344, it also protects against infection with multiple isolates of the closely related organism and causative agent of melioidosis, Burkholderia pseudomallei . Passive-transfer experiments also revealed that the protective immunity afforded by vaccination with the batA mutant strain is predominantly mediated by IgG antibodies binding to antigens expressed exclusively in vivo . Collectively, our data demonstrate that BatA is a target for developing medical countermeasures and that vaccination with a mutant lacking expression of the protein provides a platform to gain insights regarding mechanisms of protective immunity against B. mallei and B. pseudomallei , including antigen discovery.

Moraxella catarrhalis (Mcat) is a prominent mucosal pathogen causing acute otitis media (AOM). We studied Mcat nasopharyngeal (NP) colonization, AOM frequency and mucosal antibody responses to four vaccine candidate Mcat proteins: outer membrane protein (OMP) CD, oligopeptide permease (Opp) A, hemagglutinin (Hag), and Pilin A clade 2 (PilA2) from stringently defined otitis prone (sOP) children, who experience the greatest burden of disease, compared to non-otitis prone (NOP) children. sOP children had higher NP colonization of Mcat (30 vs. 22%, P = 0.0003) and Mcat-caused AOM rates (49 vs. 24%, P

The major phospholipid constituents of Moraxella catarrhalis membranes are phosphatidylglycerol, phosphatidylethanolamine, and cardiolipin (CL). However, very little is known regarding the synthesis and function of these phospholipids in M. catarrhalis. In this study, we discovered that M. catarrhalis expresses a cardiolipin synthase (CLS), termed MclS, that is responsible for the synthesis of CL within the bacterium. The nucleotide sequence of mclS is highly conserved among M. catarrhalis isolates and is predicted to encode a protein with significant amino acid similarity to the recently characterized YmdC/ClsC protein of Escherichia coli. Isogenic mclS mutant strains were generated in M. catarrhalis isolates O35E, O12E, and McGHS1 and contained no observable levels of CL. Site-directed mutagenesis of a highly conserved HKD motif of MclS also resulted in a CL-deficient strain. Moraxella catarrhalis, which depends on adherence to epithelial cells for colonization of the human host, displays significantly reduced levels of adherence to HEp-2 and A549 cell lines in the mclS mutant strains compared to wild-type bacteria. The reduction in adherence appears to be attributed to the absence of CL. These findings mark the first instance in which a CLS has been related to a virulence-associated trait.

Burkholderia pseudomallei and Burkholderia mallei are pathogenic bacteria causing fatal infections in animals and humans. Both organisms are classified as Tier 1 Select Agents owing to their highly fatal nature, potential/prior use as bioweapons, severity of disease via respiratory exposure, intrinsic resistance to antibiotics, and lack of a current vaccine. Disease manifestations range from acute septicemia to chronic infection, wherein the facultative intracellular lifestyle of these organisms promotes persistence within a broad range of hosts. This ability to thrive intracellularly is thought to be related to exploitation of host immune response signaling pathways. There are currently considerable gaps in our understanding of the molecular strategies employed by these pathogens to modulate these pathways and evade intracellular killing. A better understanding of the specific molecular basis for dysregulation of host immune responses by these organisms will provide a stronger platform to identify novel vaccine targets and develop effective countermeasures.

Most Moraxella catarrhalis isolates express a highly-conserved outer membrane protein of 453 residues designated OMPCD, which has been previously shown to mediate binding to A549 human lung cells. Here, it is reported that two distinct domains of the M. catarrhalis strain O35E OMPCD protein specify adherence. Truncated proteins were expressed in Escherichia coli to demonstrate that OMPCD residues 1–240 as well as 241–400 are important for attachment to A549 cells, and database searches indicated that amino acids 285–299 resemble an adhesive motif found in eukaryotic proteins termed thrombospondin-type 3 repeat (TT3R). Cellular enzyme-linked immunosorbent assay using His-tagged proteins demonstrated that residues 236–300 of OMPCD, containing the TT3R motif, specify adhesive properties. Furthermore, these assays revealed that a purified protein encompassing residues 16–236 binds to A549 cells. The two cell-binding domains of OMPCD were further defined to amino acids 16–150 and 261–300 by utilizing a surface-display system, which was constructed from the M. catarrhalis autotransporter protein McaP, to express foreign peptides on the surface of recombinant bacteria.

The protein McaP was previously shown to be an adhesin expressed by the Moraxella catarrhalis strain O35E, which also displays esterase and phospholipase B activities (J. M. Timpe et al., Infect. Immun. 71:4341-4350, 2003). In the present study, sequence analysis suggests that McaP is a conventional autotransporter protein that contains a 12-stranded β-barrel transporter module (amino acids [aa] 383 to 650) linked to a surface-exposed passenger domain exhibiting lipolytic activity (aa 62 to 330). An in-frame deletion removing most of this predicted N-terminal passenger domain was engineered, and Escherichia coli expressing the truncated McaP protein exhibited greatly reduced adherence to A549 human lung epithelial cells compared to E. coli expressing wild-type McaP. Site-directed mutagenesis of a serine residue at position 62 of McaP, predicted to be important for the lipolytic activity of the protein, resulted in loss of hydrolysis of p- nitrophenyl ester of caproate. E. coli expressing this mutated McaP, however, adhered to A549 monolayers at levels greater than recombinant bacteria expressing the wild-type adhesin. These results indicate that the predicted passenger domain of McaP is involved in both the binding and the lipolytic activity of the molecule and demonstrate that the adhesive properties of McaP do not require its lipolytic activity. Sequence analysis of mcaP from eight Moraxella catarrhalis strains revealed that the gene product is highly conserved at the amino acid level (98 to 100% identity), and Western blot analysis demonstrated that a panel of 16 isolates all express McaP. Flow cytometry experiments using antibodies raised against various portions of McaP indicated that its predicted passenger domain as well as transporter module contain surface-exposed epitopes. In addition to binding to the surface of intact bacteria, these antibodies were found to decrease adherence of M. catarrhalis to A549 human lung cells by up to 47% and to reduce binding of recombinant E. coli expressing McaP by 98%. These results suggest that McaP should be considered as a potential vaccine antigen.

Burkholderia mallei is a highly pathogenic bacterium that causes the zoonosis glanders. Previous studies indicated that the genome of the organism contains eight genes specifying autotransporter proteins, which are important virulence factors of Gram-negative bacteria. In the present study, we report the characterization of one of these autotransporters, BpaB. Database searches identified the bpaB gene in ten B. mallei isolates and the predicted proteins were 99-100% identical. Comparative sequence analyses indicate that the gene product is a trimeric autotransporter of 1,090 amino acids with a predicted molecular weight of 105-kDa. Consistent with this finding, we discovered that recombinant bacteria expressing bpaB produce a protein of ≥ 300-kDa on their surface that is reactive with a BpaB-specific monoclonal antibody. Analysis of sera from mice infected with B. mallei indicated that animals produce antibodies against BpaB during the course of disease, thus establishing production of the autotransporter in vivo. To gain insight on its role in virulence, we inactivated the bpaB gene of B. mallei strain ATCC 23344 and determined the median lethal dose of the mutant in a mouse model of aerosol infection. These experiments revealed that the bpaB mutation attenuates virulence 8-14 fold. Using a crystal violet-based assay, we also discovered that constitutive production of BpaB on the surface of B. mallei promotes biofilm formation. To our knowledge, this is the first report of a biofilm factor for this organism.

Francisella tularensis is a highly pathogenic bacterium; however, little is known about its initial interactions with mucosal surfaces of the human respiratory tract. To investigate these interactions, we tested whether two Francisella strains could adhere to A549 human lung epithelial cells. We found that LVS adhered well to these cells while Francisella novicida adhered poorly. We used surface biotinylation to identify bacterial proteins that might mediate this adherence. We report the identification of the F. tularensis surface protein FsaP, which, when expressed in nonadherent Escherichia coli, confers recombinant bacteria with the ability to bind to A549 cells.

Many strains of Moraxella catarrhalis are resistant to the bactericidal activity of normal human serum. Previous studies have shown that mutations involving the insertion of an antibiotic resistance cartridge into the M. catarrhalis uspA2 gene resulted in the conversion of a serum-resistant strain to a serum-sensitive phenotype. In the present study, the deletion of the entire uspA2 gene from the serum-resistant M. catarrhalis strain O35E resulted in a serum-sensitive phenotype and did not affect either the rate of growth or the lipooligosaccharide expression profile of this mutant. Inactivation of the classical complement pathway in normal human serum with Mg 2+ and EGTA resulted in the survival of this uspA2 mutant. In contrast, blocking of the alternative complement pathway did not protect this uspA2 mutant from complement-mediated killing. To determine whether the UspA2 protein is directly involved in serum resistance, transformation and allelic exchange were used to replace the uspA2 gene in the serum-resistant strain O35E with the uspA2 gene from the serum-sensitive M. catarrhalis strain MC317. The resultant O35E transformant exhibited a serum-sensitive phenotype. Similarly, when the uspA2 gene from the serum-resistant strain O35E was used to replace the uspA2 gene in the serum-sensitive strain MC317, the MC317 transformant acquired serum resistance. The use of hybrid O35E-MC317 uspA2 genes showed that the N-terminal half of the O35E protein contained a 102-amino-acid region that was involved in the expression of serum resistance. In addition, when the uspA2 genes from strains O35E and MC317 were cloned and expressed in Haemophilus influenzae DB117, only the O35E UspA2 protein caused a significant increase in the serum resistance of the H. influenzae recombinant strain. These results prove that the UspA2 protein is directly involved in the expression of serum resistance by certain M. catarrhalis strains.

Previous studies have demonstrated that the Moraxella catarrhalis surface antigen UspA1 is an adhesin for Chang human conjunctival cells. The present report demonstrates that lack of UspA1 expression does not affect the adherence of strain O35E to A549 human lung cells or primary cultures of human middle ear epithelial (HMEE) cells. These results imply that another molecule mediates the adherence of M. catarrhalis to these two cell lines. To identify this adhesin, strain O35E was mutagenized with a transposon and 1,000 mutants were screened in a microcolony formation assay using A549 cells. Nine independent isolates exhibited an 8- to 19-fold reduction in adherence and contained a transposon in the same locus. Nucleotide sequence data and PCR analysis indicated that the transposons were inserted in different locations in the gene encoding the surface protein Hag. Quantitative assays using one representative transposon mutant, O35E.TN2, showed considerably decreased binding to A549 as well as HMEE cells. However, this mutant adhered at wild-type levels to Chang conjunctival cells. These findings suggest that the M. catarrhalis Hag protein is an adhesin for cell lines derived from human lung and middle ear tissues.

Previous studies correlated the presence of a 200-kDa protein on the surface ofMoraxella catarrhaliswith the ability of this organism to agglutinate human erythrocytes (M. Fitzgerald, R. Mulcahy, S. Murphy, C. Keane, D. Coakley, and T. Scott, FEMS Immunol. Med. Microbiol. 18:209-216, 1997). In the present study, the gene encoding the 200-kDa protein (designated Hag) ofM. catarrhalisstrain O35E was subjected to nucleotide sequence analysis and then was inactivated by insertional mutagenesis. The isogenichagmutant was unable to agglutinate human erythrocytes and lost its ability to autoagglutinate but was still attached at wild-type levels to several human epithelial cell lines. Thehagmutation also eliminated the ability of this mutant strain to bind human immunoglobulin D. The presence of the Hag protein on theM. catarrhaliscell surface, as well as that of the UspA1 and UspA2 proteins (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367-4377, 1997), was investigated by transmission electron and cryoimmunoelectron microscopy. Wild-typeM. catarrhalisstrain O35E possessed a dense layer of surface projections, whereas an isogenicuspA1 uspA2 hagtriple mutant version of this strain did not possess any detectable surface projections. Examination of auspA1 uspA2double mutant that expressed the Hag protein revealed the presence of a relatively sparse layer of surface projections, similar to those seen on auspA2 hagmutant that expressed UspA1. In contrast, auspA1 hagmutant that expressed UspA2 formed a very dense layer of relatively short surface projections. These results indicate that the surface-exposed Hag protein and UspA1 and UspA2 have the potential to interact both with each other and directly with host defense systems.

Infection of susceptible hosts by the encapsulated Gram-negative bacterium Burkholderia pseudomallei (Bp) causes melioidosis, with septic patients attaining mortality rates ≥40%. Due to its high infectivity through inhalation and limited effective therapies, Bp is considered a potential bioweapon. Thus, there is great interest in identifying immune effectors that effectively kill Bp. Our goal is to compare the relative abilities of murine macrophages and neutrophils to clear Bp, as well as determine the importance of serum opsonins and bacterial capsule. Our findings indicate that murine macrophages and neutrophils are inherently unable to clear either unopsonized Bp or the relatively-avirulent acapsular bacterium B. thailandensis (Bt). Opsonization of Bp and Bt with complement or pathogen-specific antibodies increases macrophage-uptake, but does not promote clearance, although antibody-binding enhances complement deposition. In contrast, complement opsonization of Bp and Bt causes enhanced uptake and killing by neutrophils, which is linked with rapid ROS induction against bacteria exhibiting a threshold level of complement deposition. Addition of bacteria-specific antibodies enhances complement deposition, but antibody-binding alone cannot elicit neutrophil clearance. Bp capsule provides some resistance to complement deposition, but is not anti-phagocytic or protective against reactive oxygen species (ROS)-killing. Macrophages were observed to efficiently clear Bp only after pre-activation with IFNγ, which is independent of serum- and/or antibody-opsonization. These studies indicate that antibody-enhanced complement activation is sufficient for neutrophil-clearance of Bp, whereas macrophages are ineffective at clearing serum-opsonized Bp unless pre-activated with IFNγ. This suggests that effective immune therapies would need to elicit both antibodies and Th1-adaptive responses for successful prevention/eradication of melioidosis., Author Summary Burkholderia pseudomallei is the causative agent of melioidosis, which is a major cause of septic death in endemic areas of Southeast Asia and northern Australia. This range now appears to be expanding, and with the increased incidence of diabetes, which is a major predisposing factor for B. pseudomallei infections, it is believed these cases will continue to increase. This organism is also categorized as a Tier 1 select agent with great potential for misuse as a bioweapon. Thus, there is great interest in developing vaccines and other immunotherapies for melioidosis. To better design these treatments, it is essential to understand which immune cells are capable of controlling B. pseudomallei, particularly during early stages of infection, and which immune mediators are required for these cells to optimally eradicate these bacteria. In this work, we identified that both macrophages and neutrophils were capable of internalizing and killing B. pseudomallei, but required different immune mediators to allow these effects. Complement and antibody-mediated opsonization was sufficient to promote uptake and killing of B. pseudomallei by neutrophils, whereas these opsonins could only enhance uptake by macrophages; macrophage-mediated killing required IFNγ. These findings suggest that successful therapies must elicit complement-activating antibodies and IFNγ to eradicate/prevent melioidosis.

Moraxella (Branhamella) catarrhalis is an unencapsulated gram-negative bacterium that can cause both upper and lower respiratory tract infections (14, 33). It has been estimated that M. catarrhalis causes approximately 20% of cases of acute bacterial otitis media in infants and young children (5) and is associated with nearly 30% of infectious exacerbations of chronic obstructive pulmonary disease in adults (17). The significant morbidity associated with M. catarrhalis infections as well as the substantial health care costs of these infections have prompted recent interest in the development of an M. catarrhalis vaccine (37). Proteins present in or closely associated with the outer membrane of M. catarrhalis strains obtained from diverse geographic and clinical sources display highly similar patterns when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (4) and have received the most attention as potential vaccine candidates. Several of these cell surface-exposed proteins have been characterized in some detail, including UspA1, UspA2 (HMWP), and UspA2H (24, 26, 32); OMP CD (21, 34); the iron-regulated CopB protein (3, 8); the LbpA and LbpB proteins (6); and the TbpA and TbpB proteins (7, 28, 35). Little is known about the regulation of expression of M. catarrhalis outer membrane proteins. Campagnari et al. (8) were the first to show that the availability of iron in the growth medium affected expression of several M. catarrhalis outer membrane proteins. A spontaneous mutant of M. catarrhalis that lacked the ability to express several different outer membrane antigens was described by Murphy and coworkers (25). In addition, it was reported that one strain of M. catarrhalis could give rise to variants that expressed a truncated UspA2 protein (K. R. VanDerMeid, S. M. Baker, and J. C. McMichael, Abstr. 99th Gen. Meet. Am. Soc. Microbiol. 1999, abstr. D/B-289, p. 256, 1999). Most recently, it was reported that the 200-kDa surface protein of this organism, which may be involved in hemagglutination (15), underwent phase-variable expression that involved apparent slipped-strand mispairing in a homopolymeric nucleotide repeat located within the open reading frame (ORF) encoding this protein. (K. Sasaki, L. Myers, S. M. Loosmore, and M. H. Klein, Abstr. 99th Gen. Meet. Am. Soc. Microbiol., 1999, abstr. B/D-306, p. 89, 1999). The UspA1 surface protein of M. catarrhalis is synthesized as an 80- to 90-kDa monomer that forms very large aggregates or complexes that are relatively resistant to heating in the presence of SDS (12, 32). This protein also has been shown to mediate attachment of this bacterium to Chang conjunctival epithelial cells in vitro (26). In the present study, expression of the M. catarrhalis UspA1 protein was found to exhibit phase variation. Nucleotide sequence analysis indicated that this phenotypic switch could be correlated with changes in the length of a homopolymeric nucleotide [poly(G)] tract located upstream of the uspA1 ORF. Primer extension, RNA slot blot, and Northern hybridization experiments revealed that UspA1 expression was regulated at the level of transcription. Cloning and expression of uspA1 genes in Haemophilus influenzae revealed that the changes in the length of the poly(G) tract were sufficient to account for the phase-variable expression of UspA1.

The tol-oprL region in Pseudomonas aeruginosa appears to be involved in pyocin uptake and required for cell viability. The complete nucleotide sequences of the tolQRA and oprL genes as well as the incomplete sequences of tolB and orf2 have been previously reported. In addition, the sequence of a P. aeruginosa iron-regulated gene ( pig6 ) has been described and found to share homology with an open reading frame located upstream of the Escherichia coli tolQRA genes (U. A. Ochsner and M. L. Vasil, Proc. Natl. Acad. Sci. USA 93:4409–4414, 1996). In this study, we cloned the remainder of the P. aeruginosa tol-oprL gene cluster and determined its nucleotide sequence. This cluster was found to consist of seven genes in the order orf1 tolQ tolR tolA tolB oprL orf2 . Transcriptional analysis of this gene cluster was performed by detecting the presence of mRNAs spanning adjacent genes as well as by using a promoterless lacZ reporter gene fused to each of the seven genes contained in the tol-oprL locus. The results show that there are three major transcriptional units or operons in this region, orf1-tolQRA , tolB , and oprL-orf2 , in contrast to the E. coli tol-pal region, where there are only two operons, orf1-tolQRA and tolB-pal-orf2 . Analysis of gene expression indicated that the tol-oprL genes of P. aeruginosa are both iron and growth phase modulated. The first operon, orf1-tolQRA , is iron regulated throughout growth, but iron-regulated expression of tolB and oprL fusions occurs only in late log phase. The expression of the three operons was significantly less repressed by iron in fur mutants than in the wild-type strain, suggesting the involvement of Fur in the iron regulation of all three operons. RegA is a positive yet nonessential regulator of tol-oprL expression.

The UspA1 and UspA2 proteins of Moraxella catarrhalis are structurally related, are exposed on the bacterial cell surface, and migrate as very high-molecular-weight complexes in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Previous analysis of uspA1 and uspA2 mutants of M. catarrhalis strain 035E indicated that UspA1 was involved in adherence of this organism to Chang conjunctival epithelial cells in vitro and that expression of UspA2 was essential for resistance of this strain to killing by normal human serum (C. Aebi, E. R. Lafontaine, L. D. Cope, J. L. Latimer, S. R. Lumbley, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 66:3113–3119, 1998). In the present study, isogenic uspA1 , uspA2 , and uspA1 uspA2 mutations were constructed in three additional M. catarrhalis strains: 012E, TTA37, and 046E. The uspA1 mutant of strain 012E had a decreased ability to attach to Chang cells. However, inactivation of the uspA1 gene in both strain TTA37 and strain 046E did not cause a significant decrease in attachment ability. Inactivation of the uspA2 gene of strain TTA37 did result in a loss of attachment ability. Nucleotide sequence analysis revealed that the predicted protein encoded by the uspA2 genes of both strains TTA37 and 046E had a N-terminal half that resembled the N-terminal half of UspA1 proteins, whereas the C-terminal half of this protein was nearly identical to those of previously characterized UspA2 proteins. The gene encoding this “hybrid” protein was designated uspA2H . PCR-based analysis revealed that approximately 20% of M. catarrhalis strains apparently possess a uspA2H gene instead of a uspA2 gene. The M. catarrhalis uspA1 , uspA2 , and uspA2H genes were cloned and expressed in Haemophilus influenzae cells, which were used to prove that both the UspA1 and UspA2H proteins can function as adhesins in vitro.

The uspA1 and uspA2 genes of M. catarrhalis O35E encode two different surface-exposed proteins which were previously shown to share a 140-amino-acid region with 93% identity (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367–4377, 1997). The N-terminal amino acid sequences of the mature forms of both UspA1 and UspA2 from strain O35E were determined after enzymatic treatment to remove the N-terminal pyroglutamyl residue that had blocked Edman degradation. Mass spectrometric analysis indicated that the molecular mass of UspA1 from M. catarrhalis O35E was 83,500 ± 116 Da. Nucleotide sequence analysis of the uspA1 and uspA2 genes from three other M. catarrhalis strains (TTA24, ATCC 25238, and V1171) revealed that the encoded protein products were very similar to those from strain O35E. Western blot analysis was used to confirm that each of these three strains of M. catarrhalis expressed both UspA1 and UspA2 proteins. Several different and repetitive amino acid motifs were present in both UspA1 and UspA2 from these four strains, and some of these were predicted to form coiled coils. Linear DNA templates were used in an in vitro transcription-translation system to determine the sizes of the monomeric forms of the UspA1 and UspA2 proteins from strains O35E and TTA24.

The UspA surface antigen of Moraxella catarrhalis was recently shown to be comprised of two different proteins (UspA1 and UspA2) which share an internal region containing 140 amino acids with 93% identity (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367–4377, 1997). Isogenic uspA1 , uspA2 , and uspA1 uspA2 mutants were tested in a number of in vitro systems to determine what effect these mutations, either individually or together, might exert on the phenotype of M. catarrhalis 035E. Monoclonal antibodies specific for UspA1 or UspA2 were used in an indirect antibody accessibility assay to prove that both of these proteins were expressed on the surface of M. catarrhalis . All three mutants grew in vitro at the same rate and did not exhibit autoagglutination or hemagglutination properties that were detectably different from those of the wild-type parent strain. When tested for the ability to adhere to human epithelial cells, the wild-type parent strain and the uspA2 mutant readily attached to Chang conjunctival cells. In contrast, the uspA1 mutant and the uspA1 uspA2 double mutant both attached to these epithelial cells at a level nearly 2 orders of magnitude lower than that obtained with the wild-type parent strain, a result which suggested that expression of UspA1 by M. catarrhalis is essential for attachment to these epithelial cells. Both the wild-type parent strain and the uspA1 mutant were resistant to the bactericidal activity of normal human serum, whereas the uspA2 mutant and the uspA1 uspA2 double mutant were readily killed by this serum. This latter result indicated that the presence of UspA2 is essential for expression of serum resistance by M. catarrhalis .

Burkholderia pseudomallei, the etiologic agent of melioidosis, is a saprophytic bacterium readily isolated from wet soils of countries bordering the equator. Burkholderia mallei is a host-adapted clone of B. pseudomallei that does not persist outside of its equine reservoir and causes the zoonosis glanders, which is endemic in Asia, Africa, the Middle East and South America. Infection by these organisms typically occurs via percutaneous inoculation or inhalation of aerosols, and the most common manifestation is severe pneumonia leading to fatal bacteremia. Glanders and melioidosis are difficult to diagnose and require prolonged antibiotic therapy with low success rates. There are no vaccines available to protect against either Burkholderia species, and there is concern regarding their use as biological warfare agents given that B. mallei has previously been utilized in this manner. Hence, experiments were performed to establish a mouse model of aerosol infection to study the organisms and develop countermeasures. Using a hand-held aerosolizer, BALB/c mice were inoculated intratracheally with strains B. pseudomallei 1026b and B. mallei ATCC23344 and growth of the agents in the lungs, as well as dissemination to the spleen, were examined. Mice infected with 10(2), 10(3) and 10(4) organisms were unable to control growth of B. mallei in the lungs and bacteria rapidly disseminated to the spleen. Though similar results were observed in mice inoculated with 10(3) and 10(4) B. pseudomallei cells, animals infected with 10(2) organisms controlled bacterial replication in the lungs, dissemination to the spleen, and the extent of bacteremia. Analysis of sera from mice surviving acute infection revealed that animals produced antibodies against antigens known to be targets of the immune response in humans. Taken together, these data show that small volume aerosol inoculation of mice results in acute disease, dose-dependent chronic infection, and immune responses that correlate with those seen in human infections.

Moraxella catarrhalis causes significant health problems, including 15–20% of otitis media cases in children and ∼10% of respiratory infections in adults with chronic obstructive pulmonary disease. The lack of an efficacious vaccine, the rapid emergence of antibiotic resistance in clinical isolates, and high carriage rates reported in children are cause for concern. In addition, the effectiveness of conjugate vaccines at reducing the incidence of otitis media caused by Streptococcus pneumoniae and nontypeable Haemophilus influenzae suggest that M. catarrhalis infections may become even more prevalent. Hence, M. catarrhalis is an important and emerging cause of infectious disease for which the development of a vaccine is highly desirable. Studying the pathogenesis of M. catarrhalis and the testing of vaccine candidates have both been hindered by the lack of an animal model that mimics human colonization and infection. To address this, we intranasally infected chinchilla with M. catarrhalis to investigate colonization and examine the efficacy of a protein-based vaccine. The data reveal that infected chinchillas produce antibodies against antigens known to be major targets of the immune response in humans, thus establishing immune parallels between chinchillas and humans during M. catarrhalis infection. Our data also demonstrate that a mutant lacking expression of the adherence proteins MhaB1 and MhaB2 is impaired in its ability to colonize the chinchilla nasopharynx, and that immunization with a polypeptide shared by MhaB1 and MhaB2 elicits antibodies interfering with colonization. These findings underscore the importance of adherence proteins in colonization and emphasize the relevance of the chinchilla model to study M. catarrhalis–host interactions.

The tolQ, tolR, and tolA genes from Pseudomonas aeruginosa PAO were cloned using degenerate oligonucleotide PCR primers designed based on conserved transmembrane regions of Escherichia coli TolQ and TolR and E. coli and Pseudomonas putida ExbB and ExbD. The resulting PCR product was used as a probe to isolate a 6.5-kb DNA fragment containing P. aeruginosa tolQ, tolR, and tolA. The nucleotide sequence of a 2.9-kb DNA fragment containing the tolQ, tolR, and tolA genes was determined. The DNA sequence predicts TolQ to be a 25,250-Da protein exhibiting 53% identity to E. coli TolQ. TolR is predicted to be a 15,788-Da protein, sharing 38% identity with the E. coli TolR protein. The P. aeruginosa tolA sequence predicts a 37,813-Da protein with 27% identity to the E. coli TolA. The P. aeruginosa TolQRA proteins were expressed in E. coli minicells. Analysis of plasmid-encoded tolQ::lacZ and tolA::lacZ promoter fusions in E. coli indicated that these genes are expressed at different levels, suggesting transcription from different promoters. Transcriptional analysis of the tol genes in P. aeruginosa revealed that the tolQ and tolR genes are cotranscribed as an approximately 1.5-kb transcript and that tolA is transcribed from its own promoter as an approximately 1.2-kb transcript. The P. aeruginosa Tol proteins were functionally unable to complement E. coli tol mutants, although P. aeruginosa TolQ was able to complement the iron-limited growth of an E. coli exbB mutant. Introduction of the tolQRA genes in the tol-like mutant PAO 1652 restored pyocin AR41 killing, indicating that the Tol proteins are involved in the uptake of pyocin AR41 in P. aeruginosa. Attempts to inactivate the chromosomal copy of the tolA or tolQ gene in the parent strain PAO proved to be unsuccessful, and we propose that inactivation of these genes in P. aeruginosa results in a lethal phenotype.

A prospective clinical cohort study was established to investigate the humoral immune response in middle ear fluids (MEF) and serum against bacterial surface proteins in children suffering from recurrent acute otitis media (rAOM) and chronic otitis media with effusion (COME), using Luminex xMAP technology. The association between the humoral immune response and the presence of Moraxella catarrhalis and Streptococcus pneumoniae in the nasopharynx and middle ear was also studied. The levels of antigen-specific IgG, IgA, and IgM showed extensive interindividual variation. No significant differences in anti- M. catarrhalis and anti- S. pneumoniae serum and MEF median fluorescence intensity (MFI) values (anti- M. catarrhalis and antipneumococcal IgG levels) were observed between the rAOM or COME groups for all antigens tested. No significant differences were observed for M. catarrhalis and S. pneumoniae colonization and serum IgG levels against the Moraxella and pneumococcal antigens. Similar to the antibody response in serum, no significant differences in IgG, IgA, and IgM levels in MEF were observed for all M. catarrhalis and S. pneumoniae antigens between OM M. catarrhalis- or S. pneumoniae -positive and OM M. catarrhalis- or S. pneumonia -negative children suffering from either rAOM or COME. Finally, results indicated a strong correlation between antigen-specific serum and MEF IgG levels. We observed no significant in vivo expressed anti- M. catarrhalis or anti- S. pneumoniae humoral immune responses using a range of putative vaccine candidate proteins. Other factors, such as Eustachian tube dysfunction, viral load, and genetic and environmental factors, may play a more important role in the pathogenesis of OM and in particular in the development of rAOM or COME.

Background Burkholderia pseudomallei and Burkholderia mallei cause the diseases melioidosis and glanders, respectively. A well-studied aspect of pathogenesis by these closely-related bacteria is their ability to invade and multiply within eukaryotic cells. In contrast, the means by which B. pseudomallei and B. mallei adhere to cells are poorly defined. The purpose of this study was to identify adherence factors expressed by these organisms. Results Comparative sequence analyses identified a gene product in the published genome of B. mallei strain ATCC23344 (locus # BMAA0649) that resembles the well-characterized Yersinia enterocolitica autotransporter adhesin YadA. The gene encoding this B. mallei protein, designated boaA, was expressed in Escherichia coli and shown to significantly increase adherence to human epithelial cell lines, specifically HEp2 (laryngeal cells) and A549 (type II pneumocytes), as well as to cultures of normal human bronchial epithelium (NHBE). Consistent with these findings, disruption of the boaA gene in B. mallei ATCC23344 reduced adherence to all three cell types by ~50%. The genomes of the B. pseudomallei strains K96243 and DD503 were also found to contain boaA and inactivation of the gene in DD503 considerably decreased binding to monolayers of HEp2 and A549 cells and to NHBE cultures. A second YadA-like gene product highly similar to BoaA (65% identity) was identified in the published genomic sequence of B. pseudomallei strain K96243 (locus # BPSL1705). The gene specifying this protein, termed boaB, appears to be B. pseudomallei-specific. Quantitative attachment assays demonstrated that recombinant E. coli expressing BoaB displayed greater binding to A549 pneumocytes, HEp2 cells and NHBE cultures. Moreover, a boaB mutant of B. pseudomallei DD503 showed decreased adherence to these respiratory cells. Additionally, a B. pseudomallei strain lacking expression of both boaA and boaB was impaired in its ability to thrive inside J774A.1 murine macrophages, suggesting a possible role for these proteins in survival within professional phagocytic cells. Conclusions The boaA and boaB genes specify adhesins that mediate adherence to epithelial cells of the human respiratory tract. The boaA gene product is shared by B. pseudomallei and B. mallei whereas BoaB appears to be a B. pseudomallei-specific adherence factor.

Moraxella catarrhalis is a common cause of respiratory tract infection in the setting of chronic obstructive pulmonary disease (COPD). Adults with COPD acquire and clear strains of M. catarrhalis from the respiratory tract continuously and develop strain-specific protection following clearance of a strain. In previous work, we identified Hag/MID ( Moraxella immunoglobulin D-binding protein), a large multifunctional surface protein that acts as an adhesin and hemagglutinin, as a target of antibody responses in adults with COPD after clearance of M. catarrhalis . The goal of the present study was to characterize the domains of Hag/MID to which humans make antibodies, including both systemic and mucosal antibody responses. Analysis of recombinant peptide constructs, which spanned the M. catarrhalis strain O35E Hag/MID protein, with well-characterized serum and sputum samples revealed that most adults with COPD made antibodies directed toward a region of the molecule bounded by amino acids 706 to 863. Serum immunoglobulin G (IgG) and IgA purified from sputum both recognized the same domain. Some flanking sequence of this fragment was necessary for the epitope(s) in this region to maintain its conformation to bind human antibodies. These results reveal that humans consistently generate both systemic and mucosal antibody responses to an immunodominant region of the Hag/MID molecule, which was previously shown to overlap with several biologically relevant domains, including epithelial cell adherence, IgD binding, collagen binding, and hemagglutination.

Moraxella catarrhalis is a Gram-negative bacterium that has recently emerged as the third leading cause of bacterial ear infections in children. This organism is also responsible for a variety of upper respiratory tract illnesses in adults, including ∼10% of all cases of respiratory exacerbations in patients with chronic obstructive pulmonary disease (COPD). There is interest in studying M. catarrhalis for vaccine development, and this unit provides guidelines for the laboratory maintenance of the organism. The three Basic Protocols presented in this unit describe how to culture and prepare M. catarrhalis cells for use in experiments pertaining to various biological aspects of this important respiratory pathogen. Curr. Protoc. Microbiol. 11:6B.1.1-6B.1.11. © 2008 by John Wiley & Sons, Inc. Keywords: Moraxella catarrhalis; growth; laboratory; biological assays; phase variation; viability

Background The Moraxella catarrhalis Hag protein, an Oca autotransporter adhesin, has previously been shown to be important for adherence of this respiratory tract pathogen to human middle ear and A549 lung cells. Results The present study demonstrates that adherence of M. catarrhalis isogenic hag mutant strains to the human epithelial cell lines Chang (conjunctival) and NCIH292 (lung) is reduced by 50–93%. Furthermore, expressing Hag in a heterologous Escherichia coli background substantially increased the adherence of recombinant bacteria to NCIH292 cells and murine type IV collagen. Hag did not, however, increase the attachment of E. coli to Chang cells. These results indicate that Hag directly mediates adherence to NCIH292 lung cells and collagen, but is not sufficient to confer binding to conjunctival monolayers. Several in-frame deletions were engineered within the hag gene of M. catarrhalis strain O35E and the resulting proteins were tested for their ability to mediate binding to NCIH292 monolayers, middle ear cells, and type IV collagen. These experiments revealed that epithelial cell and collagen binding properties are separable, and that residues 385–705 of this ~2,000 amino acid protein are important for adherence to middle ear and NCIH292 cells. The region of O35E-Hag encompassing aa 706 to 1194 was also found to be required for adherence to collagen. In contrast, β-roll repeats present in Hag, which are structural features conserved in several Oca adhesins and responsible for the adhesive properties of Yersinia enterocolitica YadA, are not important for Hag-mediated adherence. Conclusion Hag is a major adherence factor for human cells derived from various anatomical sites relevant to pathogenesis by M. catarrhalis and its structure-function relationships differ from those of other, closely-related autotransporter proteins.

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.

Moraxella catarrhalis is a pathogen of the human airways. We found that expression of the M. catarrhalis gene mcmA by Escherichia coli increases adherence to epithelial cells 100-fold. Furthermore, we discovered that disrupting mcmA decreases M. catarrhalis adherence to laryngeal and lung cells, which are relevant to pathogenesis by the bacterium.

Moraxella catarrhalis is a human pathogen that causes otitis media in young children and lung infections in patients with chronic obstructive pulmonary disease. In this study, the role of the surface protein Hag in the adherence of multiple M. catarrhalis strains was examined. The hag genes of four clinical isolates were disrupted with a spectinomycin resistance cassette, and the binding of isogenic mutants to primary cultures of human middle ear epithelial cells (HMEE), as well as A549 pneumocytes, was measured. These experiments revealed that the attachment of most mutants to both cell types was 10-fold less than that of their wild-type progenitors. To determine whether Hag directly mediates adherence to human cells, the hag genes from three M. catarrhalis isolates were cloned and expressed in a nonadherent Escherichia coli cloning strain. At least 17-fold more E. coli bacteria expressing Hag attached to HMEE cells than an adherence-negative control. Surprisingly, Hag expression did not increase the binding of recombinant E. coli to A549 monolayers. Our data demonstrate that the involvement of Hag in M. catarrhalis adherence to A549 and HMEE cells is conserved among isolates and that Hag directly mediates binding to HMEE cells.

The pathogens Streptococcus pyogenes and Moraxella catarrhalis colonize overlapping regions of the human nasopharynx. We have found that M. catarrhalis can dramatically increase S. pyogenes adherence to human epithelial cells and that species-specific coaggregation of these bacteria correlates with this enhanced adherence.

The outer membrane protein CD (OMPCD) of Moraxella catarrhalis is an outer membrane protein with several attributes of a potential vaccine antigen. We isolated four transposon mutants of strain O35E on the basis of their reduced binding to A549 human lung cells in microcolony formation assays, and we determined that they contain a transposon in ompCD . We also found that these transposon insertions had pleiotropic effects: mutants grew slower, became serum sensitive, bound ∼10-fold less to A549 cells, and appeared transparent when grown on solid medium. We confirmed that these various phenotypes could be attributed solely to disruption of ompCD by constructing the isogenic strain O35E.CD1. O35E- ompCD was cloned, and recombinant Escherichia coli bacteria expressing the gene product exhibited a 10-fold increase in adherence to A549 cells. This is the first report of M. catarrhalis ompCD mutants, and our findings demonstrate that this gene product is an adhesin for human lung cells.

The UspA1 and Hag proteins have previously been shown to be involved in the ability of the Moraxella catarrhalis wild-type strain O35E to bind to human Chang and A549 cells, respectively. In an effort to identify novel adhesins, we generated a plasmid library of M. catarrhalis DNA fragments, which was introduced into a nonadherent Escherichia coli strain. Recombinant E. coli bacteria were subsequently enriched for clones that gained the ability to bind to Chang and A549 cells, yielding the plasmid pELFOS190. Transposon mutagenesis of this plasmid identified the potential adhesin gene mcaP ( M. catarrhalis adherence protein). Sequence analysis revealed that McaP is related to autotransporter proteins and has substantial similarity with the GDSL family of lipolytic enzymes, particularly the Moraxella bovis phospholipase B. Expression of the mcaP gene product by E. coli increased adherence to Chang, A549, and 16HBE14o − polarized human bronchial cells 50- to 100-fold. Spectrophotometric assays with p- nitrophenol derivatives also demonstrated that McaP is an esterase. Furthermore, thin-layer chromatography revealed that McaP cleaves both phosphatidylcholine and lysophosphatidylcholine. McaP releases fatty acids and glycerophosphorylcholine upon cleavage of phosphatidylcholine, thus exhibiting phospholipase B activity. The construction and characterization of isogenic M. catarrhalis O35E mutants demonstrated that the lack of McaP expression abolishes esterase activity and considerably decreases adherence to several human cell lines.

The tolQRA genes have been recently identified in Pseudomonas aeruginosa PAO. In this study, we examined the effect of iron and temperature on tolQRA expression. A promoterless lacZ gene was introduced downstream of plasmid-encoded tolQ and tolA , and expression was monitored by measuring β-galactosidase activity of cultures. Addition of 25 μM FeCl 3 to the culture medium reduced tolQRA expression by 50 to 60% in PAO but by only 25% in the fur mutant PAO A4. Northern hybridization analysis revealed that iron regulation occurs at the level of transcription and involves the P. aeruginosa ferric uptake regulator (Fur). Primer extension analysis was used to identify the proposed transcriptional start site of tolA . Although a putative Fur box was identified 20 bp upstream of the proposed start site, purified Fur did not bind to the tolA or tolQR promoter regions in an in vitro gel retardation assay. Therefore, iron regulation of the tol genes appears to involve an intermediate regulatory gene. Expression of tolQR and tolA was optimal at 37°C and was reduced by 40 to 50% when cultures were grown at either 42 or 25°C. Growth in high-iron medium at 25°C further reduced tolQR and tolA expression.

Background Moraxella catarrhalis is a human-specific gram-negative bacterium readily isolated from the respiratory tract of healthy individuals. The organism also causes significant health problems, including 15-20% of otitis media cases in children and ~10% of respiratory infections in adults with chronic obstructive pulmonary disease. The lack of an efficacious vaccine, the rapid emergence of antibiotic resistance in clinical isolates, and high carriage rates reported in children are cause for concern. Virtually all Moraxella catarrhalis isolates are resistant to β-lactam antibiotics, which are generally the first antibiotics prescribed to treat otitis media in children. The enzymes responsible for this resistance, BRO-1 and BRO-2, are lipoproteins and the mechanism by which they are secreted to the periplasm of M. catarrhalis cells has not been described. Results Comparative genomic analyses identified M. catarrhalis gene products resembling the TatA, TatB, and TatC proteins of the well-characterized Twin Arginine Translocation (TAT) secretory apparatus. Mutations in the M. catarrhalis tatA, tatB and tatC genes revealed that the proteins are necessary for optimal growth and resistance to β-lactams. Site-directed mutagenesis was used to replace highly-conserved twin arginine residues in the predicted signal sequence of M. catarrhalis strain O35E BRO-2, which abolished resistance to the β-lactam antibiotic carbanecillin. Conclusions Moraxella catarrhalis possesses a TAT secretory apparatus, which plays a key role in growth of the organism and is necessary for secretion of BRO-2 into the periplasm where the enzyme can protect the peptidoglycan cell wall from the antimicrobial activity of β-lactam antibiotics.

Background Autotransporters form a large family of outer membrane proteins specifying diverse biological traits of Gram-negative bacteria. In this study, we report the identification and characterization of a novel autotransporter gene product of Burkholderia mallei (locus tag BMA1027 in strain ATCC 23344). Results Database searches identified the gene in at least seven B. mallei isolates and the encoded proteins were found to be 84% identical. Inactivation of the gene encoding the autotransporter in the genome of strain ATCC 23344 substantially reduces adherence to monolayers of HEp-2 laryngeal cells and A549 type II pneumocytes, as well as to cultures of normal human bronchial epithelium (NHBE). Consistent with these findings, expression of the autotransporter on the surface of recombinant E. coli bacteria increases adherence to these cell types by 5–7 fold. The gene specifying the autotransporter was identified in the genome of 29 B. pseudomallei isolates and disruption of the gene in strain DD503 reduced adherence to NHBE cultures by 61%. Unlike B. mallei, the mutation did not impair binding of B. pseudomallei to A549 or HEp-2 cells. Analysis of sera from mice infected via the aerosol route with B. mallei and B. pseudomallei revealed that animals inoculated with as few as 10 organisms produce antibodies against the autotransporter, therefore indicating expression in vivo. Conclusions Our data demonstrate that we have identified an autotransporter protein common to the pathogenic species B. mallei and B. pseudomallei which mediates adherence to respiratory epithelial cells and is expressed in vivo during the course of aerosol infection.