The CRISPR-Cas System Is Involved in OmpR Genetic Regulation for Outer Membrane Protein Synthesis in Salmonella Typhi

The CRISPR-Cas cluster is found in many prokaryotic genomes including those of the Enterobacteriaceae family. Salmonella enterica serovar Typhi (S. Typhi) harbors a Type I-E CRISPR-Cas locus composed of cas3, cse1, cse2, cas7, cas5, cas6e, cas1, cas2, and a CRISPR1 array. In this work, it was determined that, in the absence of cas5 or cas2, the amount of the OmpC porin decreased substantially, whereas in individual cse2, cas6e, cas1, or cas3 null mutants, the OmpF porin was not observed in an electrophoretic profile of outer membrane proteins. Furthermore, the LysR-type transcriptional regulator LeuO was unable to positively regulate the expression of the quiescent OmpS2 porin, in individual S. Typhi cse2, cas5, cas6e, cas1, cas2, and cas3 mutants. Remarkably, the expression of the master porin regulator OmpR was dependent on the Cse2, Cas5, Cas6e, Cas1, Cas2, and Cas3 proteins. Therefore, the data suggest that the CRISPR-Cas system acts hierarchically on OmpR to control the synthesis of outer membrane proteins in S. Typhi.

The Role of a Dipeptide Transporter in the Virulence of Human Pathogen, Helicobacter pylori

Helicobacter pylori harbors a dipeptide (Dpp) transporter consisting of a substrate-binding protein (DppA), two permeases (DppB and C), and two ATPases (DppD and F). The Dpp transporter is responsible for the transportation of dipeptides and short peptides. We found that its expression is important for the growth of H. pylori. To understand the role of the Dpp transporter in the pathogenesis of H. pylori, the expression of virulence factors and H. pylori-induced IL-8 production were investigated in H. pylori wild-type and isogenic H. pylori Dpp transporter mutants. We found that expression of CagA was downregulated, while expression of type 4 secretion system (T4SS) components was upregulated in Dpp transporter mutants. The DppA mutant strain expressed higher levels of outer membrane proteins (OMPs), including BabA, HopZ, OipA, and SabA, and showed a higher adhesion level to gastric epithelial AGS cells compared with the H. pylori 26695 wild-type strain. After infection of AGS cells, H. pylori ΔdppA induced a higher level of NF-κB activation and IL-8 production compared with wild-type. These results suggested that in addition to supporting the growth of H. pylori, the Dpp transporter causes bacteria to alter the expression of virulence factors and reduces H. pylori-induced NF-κB activation and IL-8 production in gastric epithelial cells.

Thinking Outside the Bug: Targeting Outer Membrane Proteins for Burkholderia Vaccines

Increasing antimicrobial resistance due to misuse and overuse of antimicrobials, as well as a lack of new and innovative antibiotics in development has become an alarming global threat. Preventative therapeutics, like vaccines, are combative measures that aim to stop infections at the source, thereby decreasing the overall use of antibiotics. Infections due to Gram-negative pathogens pose a significant treatment challenge because of substantial multidrug resistance that is acquired and spread throughout the bacterial population. Burkholderia spp. are Gram-negative intrinsically resistant bacteria that are responsible for environmental and nosocomial infections. The Burkholderia cepacia complex are respiratory pathogens that primarily infect immunocompromised and cystic fibrosis patients, and are acquired through contaminated products and equipment, or via patient-to-patient transmission. The Burkholderia pseudomallei complex causes percutaneous wound, cardiovascular, and respiratory infections. Transmission occurs through direct exposure to contaminated water, water-vapors, or soil, leading to the human disease melioidosis, or the equine disease glanders. Currently there is no licensed vaccine against any Burkholderia pathogen. This review will discuss Burkholderia vaccine candidates derived from outer membrane proteins, OmpA, OmpW, Omp85, and Bucl8, encompassing their structures, conservation, and vaccine formulation.

A comparative whole genome analysis of Helicobacter pylori from a human dense South Asian setting

Helicobacter pylori, a Gram-negative bacterium, is associated with a wide range of gastric diseases such as gastritis, duodenal ulcer, and gastric cancer. The prevalence of H pylori and risk of disease vary in different parts of the world based on the prevailing bacterial lineage. Here, we present a contextual and comparative genomics analysis of 20 clinical isolates of H pylori from patients in Bangladesh. Despite a uniform host ethnicity (Bengali), isolates were classified as being part of the HpAsia2 (50%) or HpEurope (50%) population. Out of twenty isolates, eighteen isolates were cagA positive, with two HpEurope isolates being cagA negative, three EPIYA motif patterns (AB, AB-C, and ABC-C) were observed among the cagA-positive isolates. Three vacA genotypes were observed with the s1m1i1dic1 genotype observed in 75% of isolates; the s1m2i1d1c2 and s2m2i2d2c2 genotypes were found to be 15% and 10% of isolates, respectively. The non-virulent genotypes s2m2i2d2c2 was only observed in HpEurope population isolates. Genotypic analysis of oipA gene, present in all isolates, revealed five different patterns of the CT repeat; all HpAsia2 isolates were in "ON" while 20% of HpEurope isolates were genotypically "OFF." The three blood group antigen binding adhesins encoded genes (bab genes) examined and we observed that the most common genotype was (babA/babB/-) found in eight isolates, notably six were HpAsia2 isolates. The babA gene was found in all HpAsia2 isolates but present in only half of the HpEurope isolates. In silico antibiotic susceptibility analysis revealed that 40% of the strains were multi-drug resistant. Mutations associated with resistance to metronidazole, fluoroquinolone, and clarithromycin were detected 90%, 45%, and 5%, respectively, in H pylori strain. In conclusion, it is evident that two populations of H pylori with similar antibiotic profiles are predominant in Bangladesh, and it appears that genotypically the HpAisa2 isolates are potentially more virulent than the HpEurope isolates.

Compilation of Escherichia coli K-12 outer membrane phage receptors - their function and some historical remarks

Many Escherichia coli phages have been sequenced, but in most cases their sequences alone do not suffice to predict their host specificity. Analysis of phage resistant E. coli K-12 mutants have uncovered a certain set of outer membrane proteins and polysaccharides as receptors. In this review, a compilation of E. coli K12 phage receptors is provided and their functional characterization, often driven by studies on phage resistant mutants, is discussed in the historical context. While great progress has been made in this field thus far, several proteins in the outer membrane still await characterization as phage receptors.

Genomic Analysis of Carbapenem-Resistant Acinetobacter baumannii Isolates Belonging to Major Endemic Clones in South America

Carbapenem-resistant Acinetobacter baumannii (CRAB) are emerging worldwide. In South America, clinical isolates presenting such a phenotype usually do not belong to the globally distributed international clone 2 (IC2). The majority of these isolates are also resistant to multiple other antimicrobials and are often designated extremely drug-resistant (XDR). The aim of this study was to characterize the resistance mechanisms presented by 18 carbapenem-resistant A. baumannii isolates from five different Brazilian hospitals. Species identification was determined by rpoB sequencing, and antimicrobial susceptibility was determined by broth microdilution. Isolates were submitted to whole genome sequencing using Illumina platform and genetic similarity was determined by PFGE, MLST, and cgMLST. Genome analysis was used to identify intrinsic and acquired resistance determinants, including mutations in the AdeRSABC efflux system and in outer membrane proteins (OMPs). All isolates were identified as A. baumannii and grouped into 4 pulsotypes by PFGE, which belonged to clonal complexes (CC) 15^Pas/103^Ox (n = 4) and 79^Pas/113^Ox (n = 14), corresponding to IC4 and IC5, respectively. High MIC values to carbapenems, broad-spectrum cephalosporins, amikacin, and ciprofloxacin were observed in all isolates, while MICs of ampicillin/sulbactam, gentamicin, and tigecycline varied among the isolates. Minocycline was the most active antimicrobial agent tested. Moreover, 12 isolates (66.7%) were considered resistant to polymyxins. Besides intrinsic OXA-51 and ADC variants, all isolates harbored an acquired carbapenem-hydrolyzing class D β-lactamase (CHDL) encoding gene, either bla_OXA–23 or bla_OXA–72. A diversity of aminoglycoside modifying enzymes and resistance determinants to other antimicrobial classes were found, as well as mutations in gyrA and parC. Non-synonymous mutations have also been identified in the AdeRSABC efflux system and in most OMPs, but they were considered natural polymorphisms. Moreover, resistance to polymyxins among isolates belonging to IC5 were associated to non-synonymous mutations in pmrB, but no known polymyxin resistance mechanism was identified in isolates belonging to IC4. In conclusion, A. baumannii clinical isolates belonging to South America’s major clones present a myriad of antimicrobial resistance determinants. Special attention should be paid to natural polymorphisms observed in each clonal lineage, especially regarding non-synonymous mutations in constitutive genes associated with distinct resistance phenotypes.

Antibiotic uptake through porins located in the outer membrane of Gram-negative bacteria

Introduction: Making selective inhibitors of novel Gram-negative targets is not a substantial challenge - getting them into Gram-negative bacteria to reach their lethal target is the bottleneck. Poor permeability of the antibiotic requires high concentration causing off target activity. The lack of simple experimental techniques to measure antibiotic uptake as well as the local concentration at the target site creates a particular bottleneck in understanding and in improving the antibiotic activity.Areas covered: Here we recall current approaches to quantify the uptake. For a few antibiotics with known evidence for channel-limited permeation, the flux across a single OmpF or OmpC channel has been measured. For a typical concentration gradient of 1 µM of antibiotics the uptake varies between one up to few hundred molecules per second and per channel.Expert opinion: The current research effort is on quantifying the flux for a larger list of compounds on a cellular (mass spectra, fluorescence) or at single channel level (electrophysiology). A larger dataset of single channel permeabilities under various condition will be a powerful tool for understanding and improving the activity of antibiotics.

Development of Styrene Maleic Acid Lipid Particles as a Tool for Studies of Phage-Host Interactions

The infection of a bacterium by a phage starts with attachment to a receptor molecule on the host cell surface by the phage. Since receptor-phage interactions are crucial to successful infections, they are major determinants of phage host range and, by extension, of the broader effects that phages have on bacterial communities. Many receptor molecules, particularly membrane proteins, are difficult to isolate because their stability is supported by their native membrane environments. Styrene maleic acid lipid particles (SMALPs), a recent advance in membrane protein studies, are the result of membrane solubilizations by styrene maleic acid (SMA) copolymer chains. SMALPs thereby allow for isolation of membrane proteins while maintaining their native environment. Here, we explore SMALPs as a tool to isolate and study phage-receptor interactions. We show that SMALPs produced from taxonomically distant bacterial membranes allow for receptor-specific decrease of viable phage counts of several model phages that span the three largest phage families. After characterizing the effects of incubation time and SMALP concentration on the activity of three distinct phages, we present evidence that the interaction between two model phages and SMALPs is specific to bacterial species and the phage receptor molecule. These interactions additionally lead to DNA ejection by nearly all particles at high phage titers. We conclude that SMALPs are a potentially highly useful tool for phage-host interaction studies.IMPORTANCE Bacteriophages (viruses that infect bacteria or phages) impact every microbial community. All phage infections start with the binding of the viral particle to a specific receptor molecule on the host cell surface. Due to its importance in phage infections, this first step is of interest to many phage-related research and applications. However, many phage receptors are difficult to isolate. Styrene maleic acid lipid particles (SMALPs) are a recently developed approach to isolate membrane proteins in their native environment. In this study, we explore SMALPs as a tool to study phage-receptor interactions. We find that different phage species bind to SMALPs, while maintaining specificity to their receptor. We then characterize the time and concentration dependence of phage-SMALP interactions and furthermore show that they lead to genome ejection by the phage. The results presented here show that SMALPs are a useful tool for future studies of phage-receptor interactions.

Chitoporin from Serratia marcescens: recombinant expression, purification and crystallization

Serratia marcescens is an opportunistic pathogen that commonly causes hospital-acquired infections and can utilize chitin-enriched nutrients as an alternative energy source. This study reports the identification of a chitoporin (ChiP), termed SmChiP, from the outer membrane of S. marcescens. Sequence alignment with genetically characterized ChiPs suggests that SmChiP is more closely related to the monomeric EcChiP from Escherichia coli than to the trimeric VhChiP from Vibrio campbellii. A single crystal of SmChiP grown under the condition 22%(w/v) PEG 8000, 0.1 M calcium acetate, 0.1 M MES pH 6.0 diffracted X-ray synchrotron radiation to 1.85 Å resolution. SmChiP co-crystallized with chitohexaose under the condition 19%(w/v) PEG 1500, 2 M ammonium phosphate monobasic, 0.1 M HEPES pH 7.0 diffracted X-rays to 2.70 Å resolution. Preliminary crystallographic analysis shows that both SmChiP crystal forms contain one molecule per asymmetric unit and that they belong to the tetragonal space groups P42212 and P41212, respectively. The SmChiP crystal has unit-cell parameters a = 82.97, b = 82.97, c = 189.53 Å, α = β = γ = 90°, while the crystal of SmChiP in complex with chitohexaose has unit-cell parameters a = 73.24, b = 73.24, c = 213.46 Å, α = β = γ = 90°. Initial assessment of the complex structure clearly revealed electron density for the sugar ligand. Structure determination of SmChiP in the absence and presence of chitohexaose should reveal the molecular basis of chitin utilization by S. marcescens.

Short-Chain Fatty Acids Modulate Metabolic Pathways and Membrane Lipids in Prevotella bryantii B14

Short-chain fatty acids (SCFAs) are bacterial products that are known to be used as energy sources in eukaryotic hosts, whereas their role in the metabolism of intestinal microbes is rarely explored. In the present study, acetic, propionic, butyric, isobutyric, valeric, and isovaleric acid, respectively, were added to a newly defined medium containing Prevotella bryantii B₁4 cells. After 8 h and 24 h, optical density, pH and SCFA concentrations were measured. Long-chain fatty acid (LCFA) profiles of the bacterial cells were analyzed via gas chromatography-time of flight-mass spectrometry (GC-ToF MS) and proteins were quantified using a mass spectrometry-based, label-free approach. Cultures supplemented with single SCFAs revealed different growth behavior. Structural features of the respective SCFAs were identified in the LCFA profiles, which suggests incorporation into the bacterial membranes. The proteomes of cultures supplemented with acetic and valeric acid differed by an increased abundance of outer membrane proteins. The proteome of the isovaleric acid supplementation showed an increase of proteins in the amino acid metabolism. Our findings indicate a possible interaction between SCFAs, the lipid membrane composition, the abundance of outer membrane proteins, and a modulation of branched chain amino acid biosynthesis by isovaleric acid.

Use of recombinant Brucella outer membrane proteins 19, 25, and 31 for serodiagnosis of bovine brucellosis

Background and Aim

Brucellosis remains one of the most common zoonoses. The current anti-brucellosis measures are largely deemed ineffective due to a lack of specificity of conventional serological tests. This study evaluated the use of Brucella outer membrane protein (Omp)19 for serodiagnostic testing.

Materials and Methods

The antigenicity of recombinant Brucella Omp19, Omp25, and Omp31 was examined in serum samples from mice and rabbits immunized with Omp19 or Brucella abortus 19 whole cell (WC) and 12 and 152 cows experimentally or naturally infected with brucellosis, respectively. Serum samples were collected from 151 cows that were vaccinated with B. abortus 19 and 12 unvaccinated heifers that were maintained on a brucellosis-free farm.

Results

Immunization with Omp19 resulted in antibody production in mice after a single injection without the use of adjuvant. Serum antibodies obtained from rabbits immunized with inactivated B. abortus strain 19 WC targeted Omps by enzyme-linked immunosorbent assay (ELISA) and Western blot. Antibodies targeting Omp19 were identified in all B. abortus strain 544 experimentally infected cows at day 14 post-inoculation (p.i.); Omp25 was detected by ELISA at day 28 p.i., while an ELISA targeting Omp31 was negative for 25% of cows at this time point. Omp19 and Omp25 were readily detected by sera from cows from a new epizootic focus. Antibodies recognizing Omps were also detected in >50% of the animals maintained in a brucellosis-free herd at 10 months after vaccination.

Conclusion

Brucella Omp19 in combination with Omp25 and Omp31 may be utilized as target antigens in an ELISA designed for serological testing of unvaccinated cattle.

Single-channel properties, sugar specificity, and role of chitoporin in adaptive survival of Vibrio cholerae type strain O1

Vibrio cholerae is a Gram-negative, facultative anaerobic bacterial species that causes serious disease and can grow on various carbon sources, including chitin polysaccharides. In saltwater, its attachment to chitin surfaces not only serves as the initial step of nutrient recruitment but is also a crucial mechanism underlying cholera epidemics. In this study, we report the first characterization of a chitooligosaccharide-specific chitoporin, VcChiP, from the cell envelope of the V. cholerae type strain O1. We modeled the structure of VcChiP, revealing a trimeric cylinder that forms single channels in phospholipid bilayers. The membrane-reconstituted VcChiP channel was highly dynamic and voltage induced. Substate openings O₁', O₂', and O₃', between the fully open states O₁, O₂, and O₃, were polarity selective, with nonohmic conductance profiles. Results of liposome-swelling assays suggested that VcChiP can transport monosaccharides, as well as chitooligosaccharides, but not other oligosaccharides. Of note, an outer-membrane porin (omp)-deficient strain of Escherichia coli expressing heterologous VcChiP could grow on M9 minimal medium supplemented with small chitooligosaccharides. These results support a crucial role of chitoporin in the adaptive survival of bacteria on chitinous nutrients. Our findings also suggest a promising means of vaccine development based on surface-exposed outer-membrane proteins and the design of novel anticholera agents based on chitooligosaccharide-mimicking analogs.

Putative β-Barrel Outer Membrane Proteins of the Bovine Digital Dermatitis-Associated Treponemes: Identification, Functional Characterization, and Immunogenicity

Bovine digital dermatitis (BDD), an infectious disease of the bovine foot with a predominant treponemal etiology, is a leading cause of lameness in dairy and beef herds worldwide. BDD is poorly responsive to antimicrobial therapy and exhibits a relapsing clinical course; an effective vaccine is therefore urgently sought. Using a reverse vaccinology approach, the present study surveyed the genomes of the three BDD-associated Treponema phylogroups for putative β-barrel outer membrane proteins and considered their potential as vaccine candidates. Selection criteria included the presence of a signal peptidase I cleavage site, a predicted β-barrel fold, and cross-phylogroup homology. Four candidate genes were overexpressed in Escherichia coli BL21(DE3), refolded, and purified. Consistent with their classification as β-barrel OMPs, circular-dichroism spectroscopy revealed the adoption of a predominantly β-sheet secondary structure. These recombinant proteins, when screened for their ability to adhere to immobilized extracellular matrix (ECM) components, exhibited a diverse range of ligand specificities. All four proteins specifically and dose dependently adhered to bovine fibrinogen. One recombinant protein was identified as a candidate diagnostic antigen (disease specificity, 75%). Finally, when adjuvanted with aluminum hydroxide and administered to BDD-naive calves using a prime-boost vaccination protocol, these proteins were immunogenic, eliciting specific IgG antibodies. In summary, we present the description of four putative treponemal β-barrel OMPs that exhibit the characteristics of multispecific adhesins. The observed interactions with fibrinogen may be critical to host colonization and it is hypothesized that vaccination-induced antibody blockade of these interactions will impede treponemal virulence and thus be of therapeutic value.

A Disulfide Oxidoreductase (CHU_1165) Is Essential for Cellulose Degradation by Affecting Outer Membrane Proteins in Cytophaga hutchinsonii

Cytophaga hutchinsonii cells can bind to the surface of insoluble cellulose and degrade it by utilizing a novel cell contact-dependent mechanism, in which the outer membrane proteins may play important roles. In this study, the deletion of a gene locus, chu_1165, which encodes a hypothetical protein with 32% identity with TlpB, a disulfide oxidoreductase in Flavobacterium psychrophilum, caused a complete cellulolytic defect in C. hutchinsonii Further study showed that cells of the Δ1165 strain could not bind to cellulose, and the levels of many outer membrane proteins that can bind to cellulose were significantly decreased. The N-terminal region of CHU_1165 is anchored to the cytoplasmic membrane with five predicted transmembrane helices, and the C-terminal region is predicted to stretch to the periplasm and has a similar thioredoxin (Trx) fold containing a Cys-X-X-Cys motif that is conserved in disulfide oxidoreductases. Recombinant CHU_1165_His containing the Cys-X-X-Cys motif was able to reduce the disulfide bonds of insulin in vitro Site-directed mutation showed that the cysteines in the Cys-X-X-Cys motif and at residues 106 and 108 were indispensable for the function of CHU_1165. Western blotting showed that CHU_1165 was in an oxidized state in vivo, suggesting that it may act as an oxidase to catalyze disulfide bond formation. However, many of the decreased outer membrane proteins that were essential for cellulose degradation contained no or one cysteine, and mutation of the cysteine in these proteins did not affect cellulose degradation, indicating that CHU_1165 may have an indirect or pleiotropic effect on the function of these outer membrane proteins.IMPORTANCE Cytophaga hutchinsonii can rapidly digest cellulose in a contact-dependent manner, in which the outer membrane proteins may play important roles. In this study, a hypothetical protein, CHU_1165, characterized as a disulfide oxidoreductase, is essential for cellulose degradation by affecting the cellulose binding ability of many outer membrane proteins in C. hutchinsonii Disulfide oxidoreductases are involved in disulfide bond formation. However, our studies show that many of the decreased outer membrane proteins that were essential for cellulose degradation contained no or one cysteine, and mutation of cysteine did not affect their function, indicating that CHU_1165 did not facilitate the formation of a disulfide bond in these proteins. It may have an indirect or pleiotropic effect on the function of these outer membrane proteins. Our study provides an orientation for exploring the proteins that assist in the appropriate conformation of many outer membrane proteins essential for cellulose degradation, which is important for exploring the novel mechanism of cellulose degradation in C. hutchinsonii.

The Secretion of Toxins and Other Exoproteins of Cronobacter: Role in Virulence, Adaption, and Persistence

: Cronobacter species are considered an opportunistic group of foodborne pathogenic bacteria capable of causing both intestinal and systemic human disease. This review describes common virulence themes shared among the seven Cronobacter species and describes multiple exoproteins secreted by Cronobacter, many of which are bacterial toxins that may play a role in human disease. The review will particularly concentrate on the virulence factors secreted by C. sakazakii, C. malonaticus, and C. turicensis, which are the primary human pathogens of interest. It has been discovered that various species-specific virulence factors adversely affect a wide range of eukaryotic cell processes including protein synthesis, cell division, and ion secretion. Many of these factors are toxins which have been shown to also modulate the host immune response. These factors are encoded on a variety of mobile genetic elements such as plasmids and transposons; this genomic plasticity implies ongoing re-assortment of virulence factor genes which has complicated our efforts to categorize Cronobacter into sharply defined genomic pathotypes.

Transcriptome Analysis Reveals the Resistance Mechanism of Pseudomonas aeruginosa to Tachyplesin I

Background

Tachyplesin I is a cationic antimicrobial peptide with a typical cyclic antiparallel β-sheet structure. We previously demonstrated that long-term continuous exposure to increased concentration of tachyplesin I can induce resistant Gram-negative bacteria. However, no significant information is available about the resistance mechanism of Pseudomonas aeruginosa (P. aeruginosa) to tachyplesin I.

Materials and Methods

In this study, the global gene expression profiling of P. aeruginosa strain PA-99 and P. aeruginosa CGMCC1.2620 (PA1.2620) was conducted using transcriptome sequencing. For this purpose, outer membrane permeability and outer membrane proteins (OMPs) were further analyzed.

Results

Transcriptome sequencing detected 672 upregulated and 787 downregulated genes, covering Clusters of Orthologous Groups (COGs) of P. aeruginosa strain PA-99 compared with PA1.2620. Totally, 749 differentially expressed genes (DEGs) were assigned to 98 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and among them, a two-component regulatory system, a beta-lactam resistance system, etc. were involved in some known genes resistant to drugs. Additionally, we further attempted to indicate whether the resistance mechanism of P. aeruginosa to tachyplesin I was associated with the changes of outer membrane permeability and OMPs.

Conclusion

Our results indicated that P. aeruginosa resistant to tachyplesin I was mainly related to reduced entry of tachyplesin I into the bacterial cell due to overexpression of efflux pump, in addition to a decrease of outer membrane permeability. Our findings were also validated by pathway enrichment analysis and quantitative reverse transcription polymerase chain reaction (RT-qPCR). This study may provide a promising guidance for understanding the resistance mechanism of P. aeruginosa to tachyplesin I.

Mucin adsorbed by E. coli can affect neutrophil activation in vitro

Bacteria colonizing human intestine adhere to the gut mucosa and avoid the innate immune system. We previously demonstrated that Escherichia coli isolates can adsorb mucin from a diluted solution in vitro. Here, we evaluated the effect of mucin adsorption by E. coli cells on neutrophil activation in vitro. Activation was evaluated based on the detection of reactive oxygen species production by a chemiluminescent reaction (ChL), observation of morphological alterations in neutrophils and detection of exocytosis of myeloperoxidase and lactoferrin. We report that mucin adsorbed by cells of SharL1 isolate from Crohn's disease patient's inflamed ileum suppressed the potential for the activation of neutrophils in whole blood. Also, the binding of plasma complement proteins and immunoglobulins to the bacteria was reduced. Desialylated mucin, despite having the same adsorption efficiency to bacteria, had no effect on the blood ChL response. The effect of mucin suggests that it shields epitopes that interact with neutrophils and plasma proteins on the bacterial outer membrane. Potential candidates for these epitopes were identified among the proteins within the bacterial outer membrane fraction by 2D‐PAGE, fluorescent mucin binding on a blot and HPLC‐MS/MS. In vitro, the following proteins demonstrated mucin adsorption: outer membrane porins (OmpA, OmpC, OmpD and OmpF), adhesin OmpX, the membrane assembly factor OmpW, cobalamine transporter, ferrum uptake protein and the elongation factor Ef Tu‐1. In addition to their other functions, these proteins are known to be bacterial surface antigens. Therefore, the shielding of epitopes by mucin may affect the dynamics and intensity of an immune response.

GeTFEP: A general transfer free energy profile of transmembrane proteins

Free energy of transferring amino acid side-chains from aqueous environment into lipid bilayers, known as transfer free energy (TFE), provides important information on the thermodynamic stability of membrane proteins. In this study, we derived a TFE profile named General Transfer Free Energy Profile (GeTFEP) based on computation of the TFEs of 58 β-barrel membrane proteins (βMPs). The GeTFEP agrees well with experimentally measured and computationally derived TFEs. Analysis based on the GeTFEP shows that residues in different regions of the transmembrane (TM) segments of βMPs have different roles during the membrane insertion process. Results further reveal the importance of the sequence pattern of TM strands in stabilizing βMPs in the membrane environment. In addition, we show that GeTFEP can be used to predict the positioning and the orientation of βMPs in the membrane. We also show that GeTFEP can be used to identify structurally or functionally important amino acid residue sites of βMPs. Furthermore, the TM segments of α-helical membrane proteins can be accurately predicted with GeTFEP, suggesting that the GeTFEP is of general applicability in studying membrane protein.

Biopearling of Interconnected Outer Membrane Vesicle Chains by a Marine Flavobacterium

Large surface-to-volume ratios provide optimal nutrient uptake conditions for small microorganisms in oligotrophic habitats. The surface area can be increased with appendages. Here, we describe chains of interconnecting vesicles protruding from cells of strain Hel3_A1_48, affiliating with Formosa spp. within the Flavobacteriia and originating from coastal free-living bacterioplankton. The chains were up to 10 μm long and had vesicles emanating from the outer membrane with a single membrane and a size of 80 to 100 nm by 50 to 80 nm. Cells extruded membrane tubes in the exponential phase, whereas vesicle chains dominated on cells in the stationary growth phase. This formation is known as pearling, a physical morphogenic process in which membrane tubes protrude from liposomes and transform into chains of interconnected vesicles. Proteomes of whole-cell membranes and of detached vesicles were dominated by outer membrane proteins, including the type IX secretion system and surface-attached peptidases, glycoside hydrolases, and endonucleases. Fluorescein-labeled laminarin stained the cells and the vesicle chains. Thus, the appendages provide binding domains and degradative enzymes on their surfaces and probably storage volume in the vesicle lumen. Both may contribute to the high abundance of these Formosa-affiliated bacteria during laminarin utilization shortly after spring algal blooms.IMPORTANCE Microorganisms produce membrane vesicles. One synthesis pathway seems to be pearling that describes the physical formation of vesicle chains from phospholipid vesicles via extended tubes. Bacteria with vesicle chains had been observed as well as bacteria with tubes, but pearling was so far not observed. Here, we report the observation of, initially, tubes and then vesicle chains during the growth of a flavobacterium, suggesting biopearling of vesicle chains. The flavobacterium is abundant during spring bacterioplankton blooms developing after algal blooms and has a special set of enzymes for laminarin, the major storage polysaccharide of microalgae. We demonstrated with fluorescently labeled laminarin that the vesicle chains bind laminarin or contain laminarin-derived compounds. Proteomic analyses revealed surface-attached degradative enzymes on the outer membrane vesicles. We conclude that the large surface area and the lumen of vesicle chains may contribute to the ecological success of this marine bacterium.

Mannheimia haemolytica in bovine respiratory disease: immunogens, potential immunogens, and vaccines

Mannheimia haemolytica is the major cause of severe pneumonia in bovine respiratory disease (BRD). Early M. haemolytica bacterins were either ineffective or even enhanced disease in vaccinated cattle, which led to studies of the bacterium's virulence factors and potential immunogens to determine ways to improve vaccines. Studies have focused on the capsule, lipopolysaccharide, various adhesins, extracellular enzymes, outer membrane proteins, and leukotoxin (LKT) resulting in a strong database for understanding immune responses to the bacterium and production of more efficacious vaccines. The importance of immunity to LKT and to surface antigens in stimulating immunity led to studies of individual native or recombinant antigens, bacterial extracts, live-attenuated or mutant organisms, culture supernatants, combined bacterin-toxoids, outer membrane vesicles, and bacterial ghosts. Efficacy of several of these potential vaccines can be shown following experimental M. haemolytica challenge; however, efficacy in field trials is harder to determine due to the complexity of factors and etiologic agents involved in naturally occurring BRD. Studies of potential vaccines have led current commercial vaccines, which are composed primarily of culture supernatant, bacterin-toxoid, or live mutant bacteria. Several of those can be augmented experimentally by addition of recombinant LKT or outer membrane proteins.

Genetic Similarity of Gonococcal Homologs to Meningococcal Outer Membrane Proteins of Serogroup B Vaccine

The human pathogens Neisseria gonorrhoeae and Neisseria meningitidis share high genome identity. Retrospective analysis of surveillance data from New Zealand indicates the potential cross-protective effect of outer membrane vesicle (OMV) meningococcal serogroup B vaccine (MeNZB) against N. gonorrhoeae A licensed OMV-based MenB vaccine, MenB-4C, consists of a recombinant FHbp, NhbA, NadA, and the MeNZB OMV. Previous work has identified several abundantly expressed outer membrane proteins (OMPs) as major components of the MenB-4C OMV with high sequence similarity between N. gonorrhoeae and N. meningitidis, suggesting a mechanism for cross-protection. To build off these findings, we performed comparative genomic analysis on 970 recent N. gonorrhoeae isolates collected through a U.S surveillance system against N. meningitidis serogroup B (NmB) reference sequences. We identified 1,525 proteins that were common to both Neisseria species, of which 57 proteins were predicted to be OMPs using in silico methods. Among the MenB-4C antigens, NhbA showed moderate sequence identity (73%) to the respective gonococcal homolog, was highly conserved within N. gonorrhoeae, and was predicted to be surface expressed. In contrast, the gonococcal FHbp was predicted not to be surface expressed, while NadA was absent in all N. gonorrhoeae isolates. Our work confirmed recent observations (E. A. Semchenko, A. Tan, R. Borrow, and K. L. Seib, Clin Infect Dis, 2018, https://doi.org/10.1093/cid/ciy1061) and describes homologous OMPs from a large panel of epidemiologically relevant N. gonorrhoeae strains in the United States against NmB reference strains. Based on our results, we report a set of OMPs that may contribute to the previously observed cross-protection and provide potential antigen targets to guide the next steps in gonorrhea vaccine development.IMPORTANCE Gonorrhea, a sexually transmitted disease, causes substantial global morbidity and economic burden. New prevention and control measures for this disease are urgently needed, as strains resistant to almost all classes of antibiotics available for treatment have emerged. Previous reports demonstrate that cross-protection from gonococcal infections may be conferred by meningococcal serogroup B (MenB) outer membrane vesicle (OMV)-based vaccines. Among 1,525 common proteins shared across the genomes of both N. gonorrhoeae and N. meningitidis, 57 proteins were predicted to be surface expressed (outer membrane proteins [OMPs]) and thus preferred targets for vaccine development. The majority of these OMPs showed high sequence identity between the 2 bacterial species. Our results provide valuable insight into the meningococcal antigens present in the current OMV-containing MenB-4C vaccine that may contribute to cross-protection against gonorrhea and may inform next steps in gonorrhea vaccine development.

Outer Membrane Proteins of Salmonella as Potential Markers of Resistance to Serum, Antibiotics and Biocides

Salmonellosis continues to be a significant worldwide health problem. Despite rapid progress in identifying mechanisms of Salmonella virulence and resistance to chemicals, our knowledge of these mechanisms remains limited. Furthermore, it appears that the resistance to antibiotics can be amplified by ubiquitous usage of the disinfectants (biocides), both by industry and by ordinary households. Salmonella, as other Gram-negative bacteria possess outer membrane proteins (OMPs), which participate in maintaining cell integrity, adapting to environment, and interacting with infected host. Moreover, the OMPs may also contribute to resistance to antibacterials. This review summarizes the role of OMPs in Salmonella serum resistance, antibiotics resistance and cross-resistance to biocides. Although collected data do not allow to assign OMPs as markers of the Salmonella susceptibility to the above-mentioned factors, some of these proteins retain a dominant presence in certain types of resistance.

Mutation of CarO participates in drug resistance in imipenem-resistant Acinetobacter baumannii

OBJECTIVE

Acinetobacter baumannii has become an important problem because of the high drug resistance rate. The aim of this study was to assess the antimicrobial resistance profile and explore the role of membrane porin in imipenem resistance of A baumannii.

METHODS

A total of 63 isolates of imipenem-resistant A baumannii (IRAB) and 21 of imipenem-sensitive A baumannii (ISAB) were collected. Susceptibility testing to 16 kinds of antimicrobial agents was conducted by K-B method. PCR technique was used to detect carO and oprD genes, and sequencing was performed to compare the sequence between IRAB and ISAB. Three-dimensional structure model of CarO protein was established.

RESULTS

While ISAB isolates presented sensitive to most classes of antibiotics, isolates of IRAB displayed much higher resistance rate except tigecycline (3.2%), cefoperazone/sulbactam (28.6%), and minocycline (30.2%). All 84 isolates were observed carrying both carO and oprD genes. Further sequencing revealed important mutations of carO gene existed in IRAB in comparison with ISAB. Meanwhile, significant differences in three-dimensional structure of carO protein molecule were also found between IRAB and ISAB.

CONCLUSIONS

The drug resistance profile of IRAB is increasingly severe in clinical settings. Mutation of CarO was identified as one of the molecular mechanisms involved in imipenem resistance in A baumannii.

Structural and Functional Variation in Outer Membrane Polysaccharide Export (OPX) Proteins from the Two Major Capsule Assembly Pathways Present in Escherichia coli

Capsular polysaccharides (CPSs) are virulence factors for many important pathogens. In Escherichia coli, CPSs are synthesized via two distinct pathways, but both require proteins from the outer membrane polysaccharide export (OPX) family to complete CPS export from the periplasm to the cell surface. In this study, we compare the properties of the OPX proteins from the prototypical group 1 (Wzy-dependent) and group 2 (ABC transporter-dependent) pathways in E. coli K30 (Wza) and E. coli K2 (KpsD), respectively. In addition, we compare an OPX from Salmonella enterica serovar Typhi (VexA), which shares structural properties with Wza, while operating in an ABC transporter-dependent pathway. These proteins differ in distribution in the cell envelope and formation of stable multimers, but these properties do not align with acylation or the interfacing biosynthetic pathway. In E. coli K2, murein lipoprotein (Lpp) plays a role in peptidoglycan association of KpsD, and loss of this interaction correlates with impaired group 2 capsule production. VexA also depends on Lpp for peptidoglycan association, but CPS production is unaffected in an lpp mutant. In contrast, Wza and group 1 capsule production is unaffected by the absence of Lpp. These results point to complex structure-function relationships between different OPX proteins.IMPORTANCE Capsules are protective layers of polysaccharides that surround the cell surface of many bacteria, including that of Escherichia coli isolates and Salmonella enterica serovar Typhi. Capsular polysaccharides (CPSs) are often essential for virulence because they facilitate evasion of host immune responses. The attenuation of unencapsulated mutants in animal models and the involvement of protein families with conserved features make the CPS export pathway a novel candidate for therapeutic strategies. However, appropriate "antivirulence" strategies require a fundamental understanding of the underpinning cellular processes. Investigating export proteins that are conserved across different biosynthesis strategies will give important insight into how CPS is transported to the cell surface.