Role of the oligopeptide permease ABC Transporter of Moraxella catarrhalis in nutrient acquisition and persistence in the respiratory tract

TLR2 regulates Moraxella catarrhalis adhesion to and invasion into alveolar epithelial cells and mediates inflammatory responses

Moraxella catarrhalis is a major cause of chronic obstructive pulmonary disease. Toll-like receptor 2 (TLR2) plays an important role in the inflammatory response in host respiratory epithelial cells. M. catarrhalis induces an inflammatory immune response in respiratory epithelial cells that is mostly dependent on TLR2. However, the mechanisms by which this pathogen adheres to and invades the respiratory epithelium are not well understood. The present study aimed to reveal the role of TLR2 in M. catarrhalis adhesion to and invasion into alveolar epithelial cells, using molecular techniques. Pretreatment with the TLR2 inhibitor TLR2-IN-C29 enhanced M. catarrhalis adhesion to A549 cells but reduced its invasion, whereas the agonist Pam3CSK4 reduced both M. catarrhalis adhesion and invasion into A549 cells. Similarly, M. catarrhalis 73-OR strain adhesion and invasion were significantly reduced in TLR2-/- A549 cells. Moreover, the lung clearance rate of the 73-OR strain was significantly higher in TLR2-/- C57/BL6J mice than in wild-type (WT) mice. Histological analysis showed that inflammatory responses were milder in TLR2-/- C57/BL6J mice than in WT mice, which was confirmed by a decrease in cytokine levels in TLR2-/- C57/BL6J mice. Overall, these results indicate that TLR2 promoted M. catarrhalis adhesion and invasion of A549 cells and lung tissues and mediated inflammatory responses in infected lungs. This study provides important insights into the development of potential therapeutic strategies against M. catarrhalis and TLR2-induced inflammatory responses.

RNA thermometers are widespread upstream of ABC transporter genes in bacteria

RNA thermometers are temperature-sensing non-coding RNAs that regulate the expression of downstream genes. A well-characterized RNA thermometer motif discovered in bacteria is the ROSE-like element (repression of heat shock gene expression). ATP-binding cassette (ABC) transporters are a superfamily of transmembrane proteins that harness ATP hydrolysis to facilitate the export and import of substrates across cellular membranes. Through structure-guided bioinformatics, we discovered that ROSE-like RNA thermometers are widespread upstream of ABC transporter genes in bacteria. X-ray crystallography, biochemistry, and cellular assays indicate that these RNA thermometers are functional regulatory elements. This study expands the known biological role of RNA thermometers to these key membrane transporters.

Chemokines Kill Bacteria by Binding Anionic Phospholipids without Triggering Antimicrobial Resistance

Classically, chemokines coordinate leukocyte trafficking during immune responses; however, many chemokines have also been reported to possess direct antibacterial activity in vitro. Yet, the bacterial killing mechanism of chemokines and the biochemical properties that define which members of the chemokine superfamily are antimicrobial remain poorly understood. Here we report that the antimicrobial activity of chemokines is defined by their ability to bind phosphatidylglycerol and cardiolipin, two anionic phospholipids commonly found in the bacterial plasma membrane. We show that only chemokines able to bind these two phospholipids kill Escherichia coli and Staphylococcus aureus and that they exert rapid bacteriostatic and bactericidal effects against E. coli with a higher potency than the antimicrobial peptide beta-defensin 3. Furthermore, our data support that bacterial membrane cardiolipin facilitates the antimicrobial action of chemokines. Both biochemical and genetic interference with the chemokine-cardiolipin interaction impaired microbial growth arrest, bacterial killing, and membrane disruption by chemokines. Moreover, unlike conventional antibiotics, E. coli failed to develop resistance when placed under increasing antimicrobial chemokine pressure in vitro. Thus, we have identified cardiolipin and phosphatidylglycerol as novel binding partners for chemokines responsible for chemokine antimicrobial action. Our results provide proof of principle for developing chemokines as novel antibiotics resistant to bacterial antimicrobial resistance mechanisms.

Unguarded liabilities: Borrelia burgdorferi's complex amino acid dependence exposes unique avenues of inhibition

Recent reports from the Centers for Disease Control and Prevention approximate 500,000 cases of Lyme disease in the United States yearly, a significant economic burden on the healthcare system. The standard treatment for Lyme disease includes broad-spectrum antibiotics, which may be administered for extensive periods of time and result in significant impacts to the patient. Recently, we demonstrated that Borrelia burgdorferi, the causative agent of Lyme disease, is uniquely dependent upon peptide acquisition via an oligopeptide transport (Opp) system. This dependence appears unique to the spirochete; thus, the Opp system may constitute a novel and specific target for the inhibition of B. burgdorferi. For proof of concept, we conducted a pilot screen to determine if the Opp system constitutes a viable inhibitor target. OppA2 was utilized as our target protein as it is the most prolific peptide-binding protein throughout the enzootic cycle. We validated a thermal shift assay (TSA) to detect ligand binding against OppA2 and performed a high-throughput screen of 2,240 molecules from a diversity set library. The TSA results identified eight compounds (C1-8) demonstrating potential binding to OppA2, and growth assays identified C2 and C7 as inhibitors of B. burgdorferi growth. We confirmed by TSA that these two compounds interact with additional B. burgdorferi OppAs, potentially resulting in a cumulative inhibitory effect. Additionally, we showed that these compounds have no effect on Escherichia coli, a bacterium that encodes a dispensable Opp system which serves only as an ancillary nutrient transporter. These data demonstrate that the Opp system of B. burgdorferi acts as a viable drug target, with the potential for targeting multiple OppAs with a single compound. Moreover, the lack of inhibition against E. coli suggests that selective targeting of B. burgdorferi via the Opp system may be possible.

The role of bacterial ATP-binding cassette (ABC) transporters in pathogenesis and virulence: Therapeutic and vaccine potential

The ATP-binding cassette (ABC) transporter superfamily is found in all domains of life, facilitating critical biological processes through the translocation of a wide variety of substrates from, ions to proteins, across cellular membranes in an ATP-coupled process. The role of ABC transporters in eukaryotes has been well established: the facilitation of genetic diseases and multi-drug resistance (MDR) in cancer patients. In contrast, the role of ABC transporters in prokaryotes has been ambiguous due to their diverse functions and the sheer number of organisms in which they reside. This review examines the role of bacterial ABC transporters in pathogenesis and virulence, and their potential for therapeutic and vaccine application. We demonstrate how ABC transporters play a vital role in the virulence and pathogenesis of several pathogenic bacteria through the import of essential molecules, such as metal ions, amino acids, peptides, vitamins and osmoprotectants, as well as, the export of virulent determinants involved in glycoconjugate biosynthesis and Type I secretion. Furthermore, ABC exporters facilitate the persistence of pathogenic bacteria through the export of toxic xenobiotic substances, thus, contributing to the development of antimicrobial resistance. We also show that ABC transporters display considerable potential for therapeutic application through immunisation and resistance reversal. In conclusion, bacterial ABC transporters play an immense role in virulence and pathogenesis and display desirable traits for clinical use, therefore, potentially aiding in the battle against MDR.

Correlation of Moraxella catarrhalis macrolide susceptibility with the ability to adhere and invade human respiratory epithelial cells

Recently, the prevalence of macrolide-resistant Moraxella catarrhalis has been reported, especially among Chinese children. The fitness cost of resistance is reported to render the resistant bacteria less virulent. To investigate the correlation between macrolide susceptibility of M. catarrhalis and pathogenicity, the whole genome of 70 M. catarrhalis isolates belonging to four clonal complexes with different macrolide susceptibilities was sequenced. The gene products were annotated with the Gene Ontology terms. Based on 46 extracted essential virulence genes, 19 representative isolates were selected to infect type II alveolar cells (A549 cells). The ability of these isolates to adhere and invade human epithelial cells and to produce cytokines was comparatively analysed. Furthermore, mice were infected with a pair of M. catarrhalis isolates with different pathogenic behaviours and macrolide susceptibilities to examine pulmonary clearance, histological findings, and the production of cytokines. The percentages of annotations for binding, metabolic process, cellular process, and cell were non-significantly different between the macrolide-resistant and macrolide-susceptible groups. The presence of uspA2, uspA2H, pilO, lbpB, lex1, modM, mboIA, and mboIB significantly differed among the four clonal complexes and macrolide susceptibility groups. Furthermore, compared with those in macrolide-susceptible isolates, the adhesion ability was stronger (P = 0.0019) and the invasion ability was weaker (P < 0.0001) in the macrolide-resistant isolates. Mouse experiments revealed that pulmonary macrophages elicit immune responses against M. catarrhalis infection by significantly upregulating the Csf2, Il4, Il13, Il1b, Il6, Tnf, and Il18. Therefore, M. catarrhalis populations exhibited diverse pathogenicity in vitro and in vivo.

ATP-Binding Cassette Transporters: Snap-on Complexes?

ATP-binding cassette (ABC) transporters are one of the largest families of membrane proteins in prokaryotic organisms. Much is now understood about the structure of these transporters and many reviews have been written on that subject. In contrast, less has been written on the assembly of ABC transporter complexes and this will be a major focus of this book chapter. The complexes are formed from two cytoplasmic subunits that are highly conserved (in terms of their primary and three-dimensional structures) across the whole family. These ATP-binding subunits give rise to the name of the family. They must assemble with two transmembrane subunits that will typically form the permease component of the transporter. The transmembrane subunits have been found to be surprisingly diverse in structure when the whole family is examined, with seven distinct folds identified so far. Hence nucleotide-binding subunits appear to have been bolted on to a variety of transmembrane platforms during evolution, leading to a greater variety in function. Furthermore, many importers within the family utilise a further external substrate-binding component to trap scarce substrates and deliver them to the correct permease components. In this chapter, we will discuss whether assembly of the various ABC transporter subunits occurs with high fidelity within the crowded cellular environment and whether promiscuity in assembly of transmembrane and cytoplasmic components can occur. We also discuss the new AlphaFold protein structure prediction tool which predicts a new type of transmembrane domain fold within the ABC transporters that is associated with cation exporters of bacteria and plants.

Comparative genome analyses of Mycobacteroides immunogenum reveals two potential novel subspecies

Mycobacteroides immunogenum is an emerging opportunistic pathogen implicated in nosocomial infections. Comparative genome analyses may provide better insights into its genomic structure, functions and evolution. The present analysis showed that M. immunogenum has an open pan-genome. Approximately 36.8% of putative virulence genes were identified in the accessory regions of M. immunogenum. Phylogenetic analyses revealed two potential novel subspecies of M. immunogenum, supported by evidence from ANIb (average nucleotide identity using blast) and GGDC (Genome to Genome Distance Calculator) analyses. We identified 74 genomic islands (GIs) in Subspecies 1 and 23 GIs in Subspecies 2. All Subspecies 2-harboured GIs were not found in Subspecies 1, indicating that they might have been acquired by Subspecies 2 after their divergence. Subspecies 2 has more defence genes than Subspecies 1, suggesting that it might be more resistant to the insertion of foreign DNA and probably explaining why Subspecies 2 has fewer GIs. Positive selection analysis suggest that M. immunogenum has a lower selection pressure compared to non-pathogenic mycobacteria. Thirteen genes were positively selected and many were involved in virulence.

Deletion of the oligopeptide transporter Lmo2193 decreases the virulence of Listeria monocytogenes

Background

Listeria monocytogenes is a gram-positive bacterium that causes listeriosis mainly in immunocompromised hosts. It can also cause foodborne outbreaks and has the ability to adapt to various environments. Peptide uptake in gram-positive bacteria is enabled by oligopeptide permeases (Opp) in a process that depends on ATP hydrolysis by OppD and F. Previously a putative protein Lmo2193 was predicted to be OppD, but little is known about the role of OppD in major processes of L. monocytogenes, such as growth, virulence, and biofilm formation.

Objectives

To determine whether the virulence traits of L. monocytogenes are related to OppD.

Methods

In this study, lmo2193 gene deletion and complementation strains of L. monocytogenes were generated and compared with a wild-type strain for the following: adhesiveness, invasion ability, intracellular survival, proliferation, 50% lethal dose (LD₅₀) to mice, and the amount bacteria in the mouse liver, spleen, and brain.

Results

The results showed that virulence of the deletion strain was 1.34 and 0.5 orders of magnitude higher than that of the wild-type and complementation strains, respectively. The function of Lmo2193 was predicted and verified as OppD from the ATPase superfamily. Deletion of lmo2193 affected the normal growth of L. monocytogenes, reduced its virulence in cells and mice, and affected its ability to form biofilms.

Conclusions

Deletion of the oligopeptide transporter Lmo2193 decreases the virulence of L. monocytogenes. These effects may be related to OppD's function, which provides a new perspective on the regulation of oligopeptide transporters in L. monocytogenes.

Synchrony in serum antibody response to conserved proteins of Moraxella catarrhalis in young children

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 have been studied as vaccine candidates. Children who experience frequent acute otitis media (AOM) confirmed with pathogen identification by tympanocentesis are referred to as stringently-defined otitis prone (sOP). Synchrony of serum antibody responses against 5 Mcat proteins, OppA, Hag, OMP CD, PilA2, and Msp22 resulting from nasopharyngeal colonization and AOM was studied for 85 non-otitis prone (NOP) children and 34 sOP children. Changes in serum IgG were quantitated with ELISA. Serum IgG antibody levels against OppA, Hag, OMP CD, and Msp22 rose in synchrony in NOP and sOP children; that is, the proteins appeared equally and highly immunogenic in children at age 6 to 22-25 months old and then leveled off in their rise at 22-25 to 30 months old. In contrast, rises of PilA2 were slow from 6 months old and kept constant and did not level off significantly before 30 months old. OppA, Hag, OMP CD, and Msp22 elicited a synchronous acquisition of naturally-induced serum antibody in young children. A multi-valent Mcat protein vaccine combining OppA, Hag, OMP CD, and Msp22 may exhibit less antigen competition when administered as a combination vaccine in young children.

Complementation of the Mycoplasma synoviae MS-H vaccine strain with wild-type oppF1 influences its growth characteristics

The Mycoplasma synoviae (MS) vaccine strain MS-H harbours a frameshift mutation in oppF₁ (oligopeptide permease transporter) which results in expression of a truncated OppF₁. The effect of this mutation on growth and attenuation of the MS-H is unknown. In this study, the impact of the mutation on the vaccine phenotype was investigated in vitro by introducing a wild-type copy of oppF₁ gene in the MS-H genome. Wild-type oppF₁ was cloned under the vlhA promoter into an oriC vector carrying a tetracycline resistance gene. MS-H was successfully transformed with the final construct pMS-oppF₁-tetM or with a similar vector lacking oppF₁ coding sequence (pMS-tetM). The MS-H transformed with pMS-oppF₁-tetM exhibited smaller colony size than MS-H transformed with pMS-tetM. Monospecific rabbit sera against C-terminus of OppF₁ detected bands of expected size for full-length OppF₁ in the 86079/7NS parental strain of MS-H and the MS-H transformed with pMS-oppF₁-tetM, but not in MS-H and MS-H transformed with pMS-tetM. Comparison of the growth curve of MS-H transformants harvested from media with/without tetracycline was conducted using vlhA Q-PCR which revealed that MS-H transformed with pMS-tetM had a higher growth rate than MS-H transformed with pMS-oppF₁-tetM in the media with/without tetracycline. Lastly, the whole genome sequencing of MS-H transformed with pMS-oppF₁-tetM (passage 27) showed that the chromosomal copy of the mutated oppF₁ had been replaced with a wild-type version of the gene. This study reveals that the truncation of oppF₁ impacts on growth characteristics of the MS-H and provides insight into the molecular pathogenesis of MS and perhaps broader mycoplasma species.RESEARCH HIGHLIGHTS The full-length OppF₁ was expressed in Mycoplasma synoviae MS-H vaccine.Truncation of oppF₁ impacts on growth characteristics of the MS-H.Chromosomal copy of the mutated oppF₁ in MS-H was replaced with wild-type oppF₁.

Identification and Genomic Analysis of a Pathogenic Strain of Mycoplasma hyopneumoniae (TB1) Isolated from Tibetan Pigs

The present study aims to identify the species and strains of Mycoplasma hyopneumoniae isolated from Tibetan pigs (Mh TB1) at the genetic level for understanding the basis of its pathogenicity. Mh TB1 was isolated from the consolidated lungs of Tibetan pigs by liquid culture and agar plate colony method. Polymerase chain reaction (PCR) amplification of the 16S recombinant DNA (rDNA) conservative sequence and a species-specific gene (P36) of Mh provided species confirmation. PCR products were imaged on gels and shotgun sequencing was performed. DNA sequences were compared for assessing genetic similarity between Mh TB1 and Mh reference strains in the GenBank database. The isolated strains were >98% similar to the Mh reference strains. Genomic analysis revealed significant sequence conservation between Mh TB1 and the reference strains; however, differential genes were more prevalent in Mh TB1 than in other reported strains. Therefore, we concluded that Mh is a major pathogen of Tibetan pigs that cause enzootic pneumonia. The Mh TB1 strain harbors more genes and specific virulence factors, consistent with its plateau-related adaptability to hypoxia and virulence. Differential gene analysis revealed gene variations in the inclement plateau environment, enriched gene pool, and plateau adaptability of the Mh TB1 strain, which will be important for vaccine development.

Comparative genomic analyses of Mycoplasma synoviae vaccine strain MS-H and its wild-type parent strain 86079/7NS: implications for the identification of virulence factors and applications in diagnosis of M. synoviae

Mycoplasma synoviae is an economically important avian pathogen worldwide, causing respiratory disease, infectious synovitis, airsacculitis and eggshell apex abnormalities in commercial chickens. Despite the widespread use of MS-H as a live attenuated vaccine over the past two decades, the precise molecular basis for loss of virulence in this vaccine is not yet fully understood. To address this, the whole genome sequence of the vaccine parent strain, 86079/7NS, was obtained and compared to that of the MS-H vaccine. Except for the vlhA expressed region, both genomes were nearly identical. Thirty-two single nucleotide polymorphisms (SNPs) were identified in MS-H, including 11 non-synonymous mutations that were predicted, by bioinformatics analysis, to have changed the secondary structure of the deduced proteins. One of these mutations caused truncation of the oppF-1 gene, which encodes the ATP-binding protein of an oligopeptide permease transporter. Overall, the attenuation of MS-H strain may be caused by the cumulative and complex effects of several mutations. The SNPs identified in MS-H were further analyzed by comparing the MS-H and 86079/7NS sequences with the strains WVU-1853 and MS53. In the genomic regions conserved between all strains, 30 SNPs were found to be unique to MS-H lineage. These results have provided a foundation for developing novel biomarkers for the detection of virulence in M. synoviae and also for designing new genotyping assays for discrimination of MS-H from field strains.

Proteomics-based discrimination of differentially expressed proteins in antibiotic-sensitive and antibiotic-resistant Salmonella Typhimurium, Klebsiella pneumoniae, and Staphylococcus aureus

This study was designed to compare the differentially expressed proteins between antibiotic-sensitive and antibiotic-resistant Salmonella Typhimurium, Klebsiella pneumonia, and Staphylococcus aureus. The susceptibilities of wild-type (WT), ciprofloxacin (CIP) and/or oxacillin (OXA)-induced, and clinically isolated resistant (CCARM) S. Typhimurium (ST^WT, ST^CIP, and ST^CCARM), K. pneumoniae (KP^WT, KP^CIP, and KP^CCARM), and S. aureus (SA^WT, SA^CIP, SA^OXA, and SA^CCARM) to antibiotics were determined using broth microdilution assay. ST^CIP was highly resistant to piperacillin (MIC > 512 μg/ml), KP^CIP was resistant to chloramphenicol (128 μg/ml) and norfloxacin (16 μg/ml), SA^CIP was resistant to fluoroquinolones (32 μg/ml), and SA^OXA was resistant to ceftriaxone (32 μg/ml). The protein profiles of antibiotic-sensitive and antibiotic-resistant strains were determined using 2-DE analysis followed by LC-MS/MS. The commonly expressed proteins of ST^WT-ST^CIP, ST^WT-ST^CCARM, KP^WT-KP^CIP, KP^WT-KP^CCARM, SA^WT-SA^CIP, SA^WT-SA^OXA, and SA^WT-SA^CCARM were 763, 677, 677, 469, 261, 259, and 226, respectively. The unique protein spots were observed 57 (6.5%), 80 (11.5%), and 68 (13.9%), respectively, for ST^CCARM, KP^CCARM, and SA^CCARM. The highly up-regulated protein, PrsA (10-fold), was observed in ST^CIP resistant to ciprofloxacin (128-fold), levofloxacin (32-fold), norfloxacin (64-fold), and piperacillin (> 16-fold). The up-regulated proteins (YadC, FimA, and RplB) in KP^CIP resistant to chloramphenicol (> 32-fold), ciprofloxacin (32-fold), levofloxacin (6-fold), norfloxacin (128-fold), and sparfloxacin (64-fold). AcrB and RpoB were up-regulated in SA^CCARM resistant to multiple antibiotics. The differentially expressed proteins were related to the antibiotic resistance of ST^WT, ST^CIP, ST^CCARM, KP^WT, KP^CIP, KP^CCARM, SA^WT, SA^CIP, SA^OXA, and SA^CCARM. The resistance-associated proteins could be useful biomarkers for detecting antibiotic-resistant pathogens.

Oligopeptide-binding protein from nontypeable Haemophilus influenzae has ligand-specific sites to accommodate peptides and heme in the binding pocket

In nontypeable Haemophilus influenzae (NTHi), the oligopeptide-binding protein (OppA) serves as the substrate-binding protein (SBP) of the oligopeptide transport system responsible for the import of peptides. We solved the crystal structure of nthiOppA in complex with hydrophobic peptides of various sizes. Our novel hexapeptide complex demonstrates the flexibility of the nthiOppA-binding cavity to expand and accommodate the longer peptide while maintaining similar protein-peptide interactions of smaller peptide complexes. In addition to acquiring peptides from the host environment, as a heme auxotroph NTHi utilizes host hemoproteins as a source of essential iron. OppA is a member of the Cluster C SBP family, and unlike other SBP families, some members recognize two distinctly different substrates. DppA (dipeptide), MppA (murein tripeptide), and SapA (antimicrobial peptides) are Cluster C proteins known to also transport heme. We observed nthiOppA shares this heme-binding characteristic and established heme specificity and affinity by surface plasmon resonance (SPR) of the four Cluster C proteins in NTHi. Ligand-docking studies predicted a distinct heme-specific cleft in the binding pocket, and using SPR competition assays, we observed that heme does not directly compete with peptide in the substrate-binding pocket. Additionally, we identified that the individual nthiOppA domains differentially contribute to substrate binding, with one domain playing a dominant role in heme binding and the other in peptide binding. Our results demonstrate the multisubstrate specificity of nthiOppA and the role of NTHi Cluster C proteins in the heme-uptake pathway for this pathogen.

Loss-of-Function Mutations in the Dpp and Opp Permeases Render Erwinia amylovora Resistant to Kasugamycin and Blasticidin S

Extensive use of the antibiotic streptomycin to control fire blight disease of apples and pears, caused by the enterobacterial plant pathogen Erwinia amylovora, leads to the development of streptomycin-resistant strains in the United States and elsewhere. Kasugamycin (Ksg) has been permitted to be used as an alternative or replacement to control this serious bacterial disease. In this study, we investigated the role of two major peptide ATP-binding cassette transporter systems in E. amylovora, the dipeptide permease (Dpp) and oligopeptide permease (Opp), in conferring sensitivity to Ksg and blasticidin S (BcS). Minimum inhibitory concentration and spot dilution assays showed that the dpp deletion mutants exhibited slightly enhanced resistance to Ksg in rich medium, whereas the opp mutant exhibited slightly enhanced resistance to Ksg in minimal medium and BcS in rich medium. Deletion of both dpp and opp conferred a higher level of resistance to Ksg in both rich and minimal media, whereas deletion of opp alone was sufficient to confer high level of resistance to BcS in minimal medium. In addition, bioinformatic analysis combined with reverse transcription-quantitative polymerase chain reaction showed that the Rcs phosphorelay system negatively regulates opp expression and the rcsB mutant was more sensitive to both Ksg and BcS in minimal medium as compared with the wild type. An electrophoresis motility shift assay further confirmed the direct binding of the RcsA/RcsB proteins to the promoter region of the opp operon. However, neither the Dpp nor the Opp permeases contributed to disease progress on immature pears, hypersensitive response on tobacco leaves, or exopolysaccharide amylovoran production. These results suggested that Ksg and BcS employ the Dpp and Opp permeases to enter E. amylovora cells and the Dpp and Opp permeases act synergistically for illicit transport of antibiotics.

Selective substrate uptake: The role of ATP-binding cassette (ABC) importers in pathogenesis

The uptake of nutrients, including metals, amino acids and peptides are required for many biological processes. Pathogenic bacteria scavenge these essential nutrients from microenvironments to survive within the host. Pathogens must utilize a myriad of mechanisms to acquire these essential nutrients from the host while mediating the effects of toxicity. Bacteria utilize several transport proteins, including ATP-binding cassette (ABC) transporters to import and expel substrates. ABC transporters, conserved across all organisms, are powered by the energy from ATP to move substrates across cellular membranes. In this review, we will focus on nutrient uptake, the role of ABC importers at the host-pathogen interface, and explore emerging therapies to combat pathogenesis. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.

Mapping Protective Regions on a Three-Dimensional Model of the Moraxella catarrhalis Vaccine Antigen Oligopeptide Permease A

A vaccine against Moraxella catarrhalis would reduce tremendous morbidity, mortality, and financial burden by preventing otitis media in children and exacerbations of chronic obstructive pulmonary disease (COPD) in adults. Oligopeptide permease A (OppA) is a candidate vaccine antigen that is (i) a nutritional virulence factor expressed on the bacterial cell surface during infection, (ii) widely conserved among strains, (iii) highly immunogenic, and (iv) a protective antigen based on its capacity to induce protective responses in immunized animals. In the present study, we show that the antibodies to OppA following vaccination mediate accelerated clearance in animals after pulmonary challenge. To identify regions of OppA that bind protective antibodies, truncated constructs of OppA were engineered and studied to map regions of OppA with surface-accessible epitopes that bind high-avidity antibodies following vaccination. Protective epitopes were located in the N and C termini of the protein. Immunization of mice with constructs corresponding to these regions (T5 and T8) induced protective responses. Studies of overlapping peptide libraries of constructs T5 and T8 with OppA immune serum identified two discrete regions on each construct. These potentially protective regions were mapped on a three-dimensional computational model of OppA, where regions with solvent-accessible amino acids were identified as three potentially protective epitopes. In all, these studies revealed two regions with three specific epitopes in OppA that induce potentially protective antibody responses following vaccination. Detection of antibodies to these regions could serve to guide vaccine formulation and as a diagnostic tool for monitoring development of protective responses during clinical trials.

Genome analysis of Mycoplasma synoviae strain MS-H, the most common M. synoviae strain with a worldwide distribution

BACKGROUND

The bacterial pathogen Mycoplasma synoviae can cause subclinical respiratory disease, synovitis, airsacculitis and reproductive tract disease in poultry and is a major cause of economic loss worldwide. The M. synoviae strain MS-H was developed by chemical mutagenesis of an Australian isolate and has been used as a live attenuated vaccine in many countries over the past two decades. As a result it may now be the most prevalent strain of M. synoviae globally. Differentiation of the MS-H vaccine from local field strains is important for epidemiological investigations and is often required for registration of the vaccine.

RESULTS

The complete genomic sequence of the MS-H strain was determined using a combination of Illumina and Nanopore methods and compared to WVU-1853, the M. synoviae type strain isolated in the USA 30 years before the parent strain of MS-H, and MS53, a more recent isolate from Brazil. The vaccine strain genome had a slightly larger number of pseudogenes than the two other strains and contained a unique 55 kb chromosomal inversion partially affecting a putative genomic island. Variations in gene content were also noted, including a deoxyribose-phosphate aldolase (deoC) fragment and an ATP-dependent DNA helicase gene found only in MS-H. Some of these sequences may have been acquired horizontally from other avian mycoplasma species.

CONCLUSIONS

MS-H was somewhat more similar to WVU-1853 than to MS53. The genome sequence of MS-H will enable identification of vaccine-specific genetic markers for use as diagnostic and epidemiological tools to better control M. synoviae.

Mucosal Infections and Invasive Potential of Nonencapsulated Streptococcus pneumoniae Are Enhanced by Oligopeptide Binding Proteins AliC and AliD

Nonencapsulated Streptococcus pneumoniae (NESp) is an emerging human pathogen that colonizes the nasopharynx and is associated with noninvasive diseases such as otitis media (OM), conjunctivitis, and nonbacteremic pneumonia. Since capsule expression was previously thought to be necessary for establishment of invasive pneumococcal disease (IPD), serotype-specific polysaccharide capsules are targeted by currently licensed pneumococcal vaccines. Yet, NESp expressing oligopeptide binding proteins AliC and AliD have been isolated during IPD. Thus, we hypothesize AliC and AliD are major NESp virulence determinants that facilitate persistence and development of IPD. Our study reveals that NESp expressing AliC and AliD have intensified virulence compared to isogenic mutants. Specifically, we demonstrate AliC and AliD enhance murine nasopharyngeal colonization and pulmonary infection and are required for OM in a chinchilla model. Furthermore, AliC and AliD increase pneumococcal survival in chinchilla whole blood and aid in resistance to killing by human leukocytes. Comparative proteome analysis revealed significant alterations in protein levels when AliC and AliD were absent. Virulence-associated proteins, including a pneumococcal surface protein C variant (CbpAC), were significantly downregulated, while starvation response indicators were upregulated in the double mutant relative to wild-type levels. We also reveal that differentially expressed CbpAC was essential for NESp adherence to epithelial cells, virulence during OM, reduction of C3b deposition on the NESp surface, and binding to nonspecific IgA. Altogether, the rise in NESp prevalence urges the need to understand how NESp establishes disease and persists in a host. This study highlights the roles of AliC, AliD, and CbpAC in the pathogenesis of NESp.

Despite the effective, widespread use of licensed pneumococcal vaccines over many decades, pneumococcal infections remain a worldwide burden resulting in high morbidity and mortality. NESp subpopulations are rapidly rising in the wake of capsule-targeted vaccine strategies, yet there is very little knowledge on NESp pathogenic potential and virulence mechanisms. Although NESp lacks a protective capsule, NESp lineages expressing AliC and AliD have been associated with systemic infections. Furthermore, higher antibiotic resistance rates and transformation efficiencies associated with emerging NESp threaten treatment strategies needed to control pneumococcal infections and transmission. Elucidating how NESp survives within a host and establishes disease is necessary for development of broadened pneumococcal prevention methods. Our study identifies virulence determinants and host survival mechanisms employed by NESp with a high pathogenic potential. Moreover, our study also identifies virulence determinants shared by NESp and encapsulated strains that may serve as broad prevention and therapeutic targets.

A Moraxella catarrhalis vaccine to protect against otitis media and exacerbations of COPD: An update on current progress and challenges

Moraxella catarrhalis is a major cause of morbidity and mortality worldwide, especially causing otitis media in young children and exacerbations of chronic obstructive pulmonary disease in adults. This pathogen uses several virulence mechanisms to colonize and survive in its host, including adherence and invasion of host cells, formation of polymicrobial biofilms with other bacterial pathogens, and production of β-lactamase. Given the global impact of otitis media and COPD, an effective vaccine to prevent M. catarrhalis infection would have a huge impact on the quality of life in both patient populations by preventing disease, thus reducing morbidity and health care costs. A number of promising vaccine antigens have been identified for M. catarrhalis. The development of improved animal models of M. catarrhalis disease and identification of a correlate of protection are needed to accelerate vaccine development. This review will discuss the current state of M. catarrhalis vaccine development, and the challenges that must be addressed to succeed.

Virulence determinants of Moraxella catarrhalis: distribution and considerations for vaccine development

Moraxella catarrhalis is a human-restricted opportunistic bacterial pathogen of the respiratory mucosa. It frequently colonizes the nasopharynx asymptomatically, but is also an important causative agent of otitis media (OM) in children, and plays a significant role in acute exacerbations of chronic obstructive pulmonary disease (COPD) in adults. As the current treatment options for M. catarrhalis infection in OM and exacerbations of COPD are often ineffective, the development of an efficacious vaccine is warranted. However, no vaccine candidates for M. catarrhalis have progressed to clinical trials, and information regarding the distribution of M. catarrhalis virulence factors and vaccine candidates is inconsistent in the literature. It is largely unknown if virulence is associated with particular strains or subpopulations of M. catarrhalis, or if differences in clinical manifestation can be attributed to the heterogeneous expression of specific M. catarrhalis virulence factors in the circulating population. Further investigation of the distribution of M. catarrhalis virulence factors in the context of carriage and disease is required so that vaccine development may be targeted at relevant antigens that are conserved among disease-causing strains. The challenge of determining which of the proposed M. catarrhalis virulence factors are relevant to human disease is amplified by the lack of a standardized M. catarrhalis typing system to facilitate direct comparisons of worldwide isolates. Here we summarize and evaluate proposed relationships between M. catarrhalis subpopulations and specific virulence factors in the context of colonization and disease, as well as the current methods used to infer these associations.

A Cation-Binding Surface Protein as a Vaccine Antigen To Prevent Moraxella catarrhalis Otitis Media and Infections in Chronic Obstructive Pulmonary Disease

Moraxella catarrhalis is an exclusively human respiratory tract pathogen that is a common cause of otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease. A vaccine to prevent these infections would have a major impact on reducing the substantial global morbidity and mortality in these populations. Through a genome mining approach, we identified AfeA, an ∼32-kDa substrate binding protein of an ABC transport system, as an excellent candidate vaccine antigen. Recombinant AfeA was expressed and purified and binds ferric, ferrous, manganese, and zinc ions, as demonstrated by thermal shift assays. It is a highly conserved protein that is present in all strains of M. catarrhalis Immunization with recombinant purified AfeA induces high-titer antibodies that recognize the native M. catarrhalis protein. AfeA expresses abundant epitopes on the bacterial surface and induces protective responses in the mouse pulmonary clearance model following aerosol challenge with M. catarrhalis Finally, AfeA is expressed during human respiratory tract infection of adults with chronic obstructive pulmonary disease (COPD). Based on these observations, AfeA is an excellent vaccine antigen to be included in a vaccine to prevent infections caused by M. catarrhalis.

Stringently Defined Otitis Prone Children Demonstrate Deficient Naturally Induced Mucosal Antibody Response to Moraxella catarrhalis Proteins

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 < 0.0001) than NOP children. Natural acquisition of mucosal antibodies to Mcat proteins OMP CD (IgG, P < 0.0001), OppA (IgG, P = 0.018), Hag (IgG and IgA, both P < 0.0001), and PilA2 (IgA, P < 0.0001) was lower in sOP than NOP children. Higher levels of mucosal IgG to Hag (P = 0.039) and PilA2 (P = 0.0076), and IgA to OMP CD (P = 0.010), OppA (P = 0.030), and PilA2 (P = 0.043) were associated with lower carriage of Mcat in NOP but not sOP children. Higher levels of mucosal IgG to OMP CD (P = 0.0070) and Hag (P = 0.0003), and IgA to Hag (P = 0.0067) at asymptomatic colonization than those at onset of AOM were associated with significantly lower rate of Mcat NP colonization progressing to AOM in NOP compared to sOP children (3 vs. 26%, P < 0.0001). In conclusion, sOP children had a diminished mucosal antibody response to Mcat proteins, which was associated with higher frequencies of asymptomatic NP colonization and NP colonization progressing to Mcat-caused AOM. Enhancing Mcat antigen-specific mucosal immune responses to levels higher than achieved by natural exposure will be necessary to prevent AOM in sOP children.

Serum antibody response to Moraxella catarrhalis proteins in stringently defined otitis prone children

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 6-36months 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 6-36months, 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.

Panel 6: Vaccines

Objective To review the literature on progress regarding (1) effectiveness of vaccines for prevention of otitis media (OM) and (2) development of vaccine antigens for OM bacterial and viral pathogens. Data Sources PubMed database of the National Library of Science. Review Methods We performed literature searches in PubMed for OM pathogens and candidate vaccine antigens, and we restricted the searches to articles in English that were published between July 2011 and June 2015. Panel members reviewed literature in their area of expertise. Conclusions Pneumococcal conjugate vaccines (PCVs) are somewhat effective for the prevention of pneumococcal OM, recurrent OM, OM visits, and tympanostomy tube insertions. Widespread use of PCVs has been associated with shifts in pneumococcal serotypes and bacterial pathogens associated with OM, diminishing PCV effectiveness against AOM. The 10-valent pneumococcal vaccine containing Haemophilus influenzae protein D (PHiD-CV) is effective for pneumococcal OM, but results from studies describing the potential impact on OM due to H influenzae have been inconsistent. Progress in vaccine development for H influenzae, Moraxella catarrhalis, and OM-associated respiratory viruses has been limited. Additional research is needed to extend vaccine protection to additional pneumococcal serotypes and other otopathogens. There are likely to be licensure challenges for protein-based vaccines, and data on correlates of protection for OM vaccine antigens are urgently needed. Implications for Practice OM continues to be a significant health care burden globally. Prevention is preferable to treatment, and vaccine development remains an important goal. As a polymicrobial disease, OM poses significant but not insurmountable challenges for vaccine development.

The oppD Gene and Putative Peptidase Genes May Be Required for Virulence in Mycoplasma gallisepticum

Relatively few virulence genes have been identified in pathogenic mycoplasmas, so we used signature-tagged mutagenesis to identify mutants of the avian pathogen Mycoplasma gallisepticum with a reduced capacity to persist in vivo and compared the levels of virulence of selected mutants in experimentally infected chickens. Four mutants had insertions in one of the two incomplete oppABCDF operons, and a further three had insertions in distinct hypothetical genes, two containing peptidase motifs and one containing a member of a gene family. The three hypothetical gene mutants and the two with insertions in oppD₁ were used to infect chickens, and all five were shown to have a reduced capacity to induce respiratory tract lesions. One oppD₁ mutant and the MGA_1102 and MGA_1079 mutants had a greatly reduced capacity to persist in the respiratory tract and to induce systemic antibody responses against M. gallisepticum The other oppD₁ mutant and the MGA_0588 mutant had less capacity than the wild type to persist in the respiratory tract but did elicit systemic antibody responses. Although M. gallisepticum carries two incomplete opp operons, one of which has been acquired by horizontal gene transfer, our results suggest that one of the copies of oppD may be required for full expression of virulence. We have also shown that three hypothetical genes, two of which encode putative peptidases, may be required for full expression of virulence in M. gallisepticum. None of these genes has previously been shown to influence virulence in pathogenic mycoplasmas.

Bacterial peptide transporters: Messengers of nutrition to virulence

Bacteria possess numerous peptide transporters for importing peptides as nutrients. However, these peptide transporters are now consistently reported to play a role in the virulence of various bacterial pathogens. Their ability to transport peptides has implications in antibacterial therapy as well. Therefore, it would be instrumental to have complete knowledge about the role of peptide transporters in mediating this cross connection between metabolism and pathogenesis. Studies on various peptide transporters in bacterial pathogens have improved our understanding of this field. In this review, we have given an overview of the functioning of bacterial peptide transporters and their contribution in virulence of major bacterial pathogens.

Potential impact of a Moraxella catarrhalis vaccine in COPD

Moraxella catarrhalis is the second most common cause of exacerbations in adults with COPD, resulting in enormous morbidity and mortality in this clinical setting. Vaccine development for M. catarrhalis has lagged behind the other two important causes of exacerbations in COPD, nontypeable Haemophilus influenzae and Streptococcus pneumoniae. While no licensed vaccine is currently available for M. catarrhalis, several promising candidate vaccine antigens have been identified and characterized and are close to entering clinical trials. Key steps that are required to advance vaccines for M. catarrhalis along the translational pipeline include standardization of assay systems to assess candidate antigens, identification of a reliable correlate of protection and expansion of partnerships between industry, academia and government to overcome regulatory hurdles. A vaccine to prevent M. catarrhalis infections in COPD would have a major impact in reducing morbidity, mortality and healthcare costs in COPD.

Sulfate-binding protein, CysP, is a candidate vaccine antigen of Moraxella catarrhalis

Moraxella catarrhalis causes otitis media in children and respiratory tract infections in adults with chronic obstructive pulmonary disease (COPD). A vaccine to prevent M. catarrhalis infections would have an enormous impact globally in preventing morbidity caused by M. catarrhalis in these populations. Using a genome mining approach we have identified a sulfate binding protein, CysP, of an ATP binding cassette (ABC) transporter system as a novel candidate vaccine antigen. CysP expresses epitopes on the bacterial surface and is highly conserved among strains. Immunization with CysP induces potentially protective immune responses in a murine pulmonary clearance model. In view of these features that indicate CysP is a promising vaccine antigen, we conducted further studies to elucidate its function. These studies demonstrated that CysP binds sulfate and thiosulfate ions, plays a nutritional role for the organism and functions in intracellular survival of M. catarrhalis in human respiratory epithelial cells. The observations that CysP has features of a vaccine antigen and also plays an important role in growth and survival of the organism indicate that CysP is an excellent candidate vaccine antigen to prevent M. catarrhalis otitis media and infections in adults with COPD.

ATP-Binding Cassette (ABC) Transporters of the Human Respiratory Tract Pathogen, Moraxella catarrhalis: Role in Virulence

Moraxella catarrhalis is a human respiratory tract pathogen that causes otitis media (middle ear infections) in children and respiratory tract infections in adults with chronic obstructive pulmonary disease. In view of the huge global burden of disease caused by M. catarrhalis, the development of vaccines to prevent these infections and better approaches to treatment have become priorities. In previous work, we used a genome mining approach that identified three substrate binding proteins (SBPs) of ATP-binding cassette (ABC) transporters as promising candidate vaccine antigens. In the present study, we performed a comprehensive assessment of 19 SBPs of 15 ABC transporter systems in the M. catarrhalis genome by engineering knockout mutants and studying their role in assays that assess mechanisms of infection. The capacity of M. catarrhalis to survive and grow in the nutrient-limited and hostile environment of the human respiratory tract, including intracellular growth, account in part for its virulence. The results show that ABC transporters that mediate uptake of peptides, amino acids, cations and anions play important roles in pathogenesis by enabling M. catarrhalis to 1) grow in nutrient-limited conditions, 2) invade and survive in human respiratory epithelial cells and 3) persist in the lungs in a murine pulmonary clearance model. The knockout mutants of SBPs and ABC transporters showed different patterns of activity in the assay systems, supporting the conclusion that different SBPs and ABC transporters function at different stages in the pathogenesis of infection. These results indicate that ABC transporters are nutritional virulence factors, functioning to enable the survival of M catarrhalis in the diverse microenvironments of the respiratory tract. Based on the role of ABC transporters as virulence factors of M. catarrhalis, these molecules represent potential drug targets to eradicate the organism from the human respiratory tract.

Compensatory expression of multidrug-resistance genes encoding ABC transporters in dermatophytes

Genomic sequencing of several dermatophyte species has revealed that they show small differences in genetic content and genome organization, although each fungus has adapted to specific niches. Thus, it seemed relevant to compare gene expression between species. Here, we examined the transcription modulation of three ATP-binding cassette (ABC) transporter genes (pdr1, mdr2 and mdr4), which code for membrane transporter proteins in four species of Trichophyton ; T. interdigitale, T. rubrum, T. tonsurans and T. equinum . These fungal species were challenged with sub-lethal doses of griseofulvin, itraconazole, terbinafine and amphotericin B. A mutant strain of T. interdigitale, Δmdr2, was also analysed for the modulation of pdr1 and mdr4 genes to evaluate the possible functional interaction among these three genes. Disruption of the mdr2 gene resulted in the accumulation of high levels of mdr4 transcripts when challenged with griseofulvin, suggesting that the mdr4 gene is compensating for the inactivation of mdr2 by providing resistance to this antifungal. Although the three ABC transporter genes have high homology between the four dermatophytes analysed, it is likely that they have specific functions, suggesting that the action of each drug is dependent on other factors inherent to each species. Our data suggest that these ABC transporter genes act synergistically in dermatophytes, and they may compensate for one another when challenged with antifungal drugs. This may be an important cause of therapeutic failure when treating fungal infections.

The Vaccine Candidate Substrate Binding Protein SBP2 Plays a Key Role in Arginine Uptake, Which Is Required for Growth of Moraxella catarrhalis

Moraxella catarrhalis is an exclusively human pathogen that is an important cause of otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulmonary disease. A vaccine to prevent M. catarrhalis infections would have an enormous global impact in reducing morbidity resulting from these infections. Substrate binding protein 2 (SBP2) of an ABC transporter system has recently been identified as a promising vaccine candidate antigen on the bacterial surface of M. catarrhalis. In this study, we showed that SBP1, -2, and -3 individually bind different basic amino acids with exquisite specificity. We engineered mutants that each expressed a single SBP from this gene cluster and showed in growth experiments that SBP1, -2, and -3 serve a nutritional function through acquisition of amino acids for the bacterium. SBP2 mediates uptake of arginine, a strict growth requirement of M. catarrhalis. Adherence and invasion assays demonstrated that SBP1 and SBP3 play a role in invasion of human respiratory epithelial cells, consistent with a nutritional role in intracellular survival in the human respiratory tract. This work demonstrates that the SBPs of an ABC transporter system function in the uptake of basic amino acids to support growth of M. catarrhalis. The critical role of SBP2 in arginine uptake may contribute to its potential as a vaccine antigen.

Serum antibody response to Moraxella catarrhalis proteins OMP CD, OppA, Msp22, Hag, and PilA2 after nasopharyngeal colonization and acute otitis media in children

BACKGROUND

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.

METHODS

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.

RESULTS

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 (P<0.001), with a rank order as follows: Msp22=OppA>OMP 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 (P<0.05). 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.

CONCLUSIONS

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.

Vaccine targets against Moraxella catarrhalis

INTRODUCTION

Moraxella catarrhalis is a prominent pathogen that causes acute otitis media in children and lower respiratory tract infections in adults, resulting in a significant socioeconomic burden on healthcare systems globally. No vaccine is currently available for M. catarrhalis. Promising M. catarrhalis target antigens have been characterized in animal models and should soon enter human clinical trials.

AREAS COVERED

This review discusses the detailed features and research status of current candidate target antigens for an M. catarrhalis vaccine. The approaches for assessing M. catarrhalis vaccine efficacy are also discussed.

EXPERT OPINION

Targeting the key molecules contributing to serum resistance may be a viable strategy to identify effective vaccine targets among M. catarrhalis antigens. Elucidating the role and mechanisms of the serum and mucosal immune responses to M. catarrhalis is significant for vaccine target selection, testing and evaluation. Developing animal models closely simulating M. catarrhalis-caused human respiratory diseases is of great benefit in better understanding pathogenesis and evaluating vaccine efficacy. Carrying out clinical trials will be a landmark in the progress of M. catarrhalis vaccine research. Combined multicomponent vaccines will be a focus of future M. catarrhalis vaccine studies.

Expression of the Oligopeptide Permease Operon of Moraxella catarrhalis Is Regulated by Temperature and Nutrient Availability

Moraxella catarrhalis causes otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults. Together, these two conditions contribute to enormous morbidity and mortality worldwide. The oligopeptide permease (opp) ABC transport system is a nutritional virulence factor important for the utilization of peptides. The substrate binding protein OppA, which binds peptides for uptake, is a potential vaccine antigen, but little was known about the regulation of gene expression. The five opp genes oppB, oppC, oppD, oppF, and oppA are in the same open reading frame. Sequence analysis predicted two promoters, one located upstream of oppB and one within the intergenic region between oppF and oppA. We have characterized the gene cluster as an operon with two functional promoters and show that cold shock at 26°C for ≤ 0.5 h and the presence of a peptide substrate increase gene transcript levels. Additionally, the putative promoter upstream of oppA contributes to the transcription of oppA but is not influenced by the same environmental cues as the promoter upstream of oppB. We conclude that temperature and nutrient availability contribute to the regulation of the Opp system, which is an important nutritional virulence factor in M. catarrhalis.