Virulence functions of autotransporter proteins

Antigen 43 associated with Escherichia coli membrane vesicles contributes to bacterial cell association and biofilm formation

Bacterial membrane vesicles (MVs) are produced by all bacteria and contribute to numerous bacterial functions due to their ability to package and transfer bacterial cargo. In doing so, MVs have been shown to facilitate horizontal gene transfer, mediate antimicrobial activity, and promote biofilm formation. Uropathogenic Escherichia coli is a pathogenic Gram-negative organism that persists in the urinary tract of its host due to its ability to form persistent, antibiotic-resistant biofilms. The formation of these biofilms is dependent upon proteins such as Antigen 43 (Ag43), which belongs to the widespread Autotransporter group of bacterial surface proteins. In E. coli, the autotransporter Ag43 has been shown to contribute to bacterial cell aggregation and biofilm formation via self-association of Ag43 between neighboring Ag43-expressing bacteria. As MVs package bacterial proteins, we investigated whether MVs produced by E. coli contained Ag43, and the ability of Ag43-expressing MVs to facilitate cell aggregation and biofilm formation. We showed that Ag43 expressing E. coli produced MVs that contained Ag43 on their surface and had an enhanced ability to bind to E. coli bacteria. Furthermore, we demonstrated that the addition of Ag43-containing MVs to Ag43-expressing E. coli significantly enhanced biofilm formation. These findings reveal the contribution of MVs harboring autotransporters in promoting bacterial aggregation and enhancing biofilm formation, highlighting the impact of MVs and their specific composition to bacterial adaptation and pathogenesis.IMPORTANCEAutotransporter proteins are the largest family of outer membrane and secreted proteins in Gram-negative bacteria which contribute to pathogenesis by promoting aggregation, biofilm formation, persistence, and cytotoxicity. Although the roles of bacterial autotransporters are well known, the ability of bacterial membrane vesicles (MVs) naturally released from the surface of bacteria to contain autotransporters and their role in promoting virulence remains less investigated. Our findings reveal that MVs produced by E. coli contain the autotransporter protein Ag43. Furthermore, we show that Ag43-containing MVs function to enhance bacterial cell interactions and biofilm formation. By demonstrating the ability of MVs to carry functional autotransporter adhesins, this work highlights the importance of MVs in disseminating autotransporters beyond the bacterial cell membrane to ultimately promote cellular interactions and enhance biofilm development. Overall, these findings have significant implications in furthering our understanding of the numerous ways in which MVs can facilitate bacterial persistence and pathogenesis.

Antimicrobial Proficiency of Amlodipine: Investigating its Impact on Pseudomonas spp. in Urinary Tract Infections

Antibiotic resistance in urinary tract infections (UTIs) is a growing concern due to extensive antibiotic use. The study explores a drug repurposing approach to find non-antibiotic drugs with antibacterial activity. In the present study, 8 strains of Pseudomonas spp. were used that were clinically isolated from UTI-infected patients. Amlodipine, a cardiovascular drug used in this study, has shown potential antimicrobial effect in reducing the various virulence factors, including swimming and twitching motility, biofilm, rhamnolipid, pyocyanin, and oxidative stress resistance against all the strains. Amlodipine exhibited the most potent antimicrobial activity with MIC in the range of 6.25 to 25 µg/ml. Significant inhibition in biofilm production was seen in the range of 45.75 to 76.70%. A maximum decrease of 54.66% and 59.45% in swimming and twitching motility was observed, respectively. Maximum inhibition of 65.87% of pyocyanin pigment was observed with the effect of amlodipine. Moreover, a significant decrease in rhamnolipids production observed after amlodipine treatment was between 16.5 and 0.001 mg/ml as compared to the control. All bacterial strains exhibited leakage of proteins and nucleic acids from their cell membranes when exposed to amlodipine which suggests the damage of the structural integrity. In conclusion, amlodipine exhibited good antimicrobial activity and can be used as a potential candidate to be repurposed for the treatment of urinary tract infections.

Architectural dissection of adhesive bacterial cell surface appendages from a "molecular machines" viewpoint

The ability of bacteria to interact with and respond to their environment is crucial to their lifestyle and survival. Bacterial cells routinely need to engage with extracellular target molecules, in locations spatially separated from their cell surface. Engagement with distant targets allows bacteria to adhere to abiotic surfaces and host cells, sense harmful or friendly molecules in their vicinity, as well as establish symbiotic interactions with neighboring cells in multicellular communities such as biofilms. Binding to extracellular molecules also facilitates transmission of information back to the originating cell, allowing the cell to respond appropriately to external stimuli, which is critical throughout the bacterial life cycle. This requirement of bacteria to bind to spatially separated targets is fulfilled by a myriad of specialized cell surface molecules, which often have an extended, filamentous arrangement. In this review, we compare and contrast such molecules from diverse bacteria, which fulfil a range of binding functions critical for the cell. Our comparison shows that even though these extended molecules have vastly different sequence, biochemical and functional characteristics, they share common architectural principles that underpin bacterial adhesion in a variety of contexts. In this light, we can consider different bacterial adhesins under one umbrella, specifically from the point of view of a modular molecular machine, with each part fulfilling a distinct architectural role. Such a treatise provides an opportunity to discover fundamental molecular principles governing surface sensing, bacterial adhesion, and biofilm formation.

Unveiling the hidden arsenal: new insights into Proteus mirabilis virulence in UTIs

Proteus mirabilis is a Gram-negative bacterium commonly found in urinary tract infections (UTIs) and catheter-associated urinary tract infections (CAUTIs). The pathogenic mechanisms of Proteus mirabilis are complex and diverse, involving various virulence factors, including fimbriae, flagella, urease, polyphosphate kinase, lipopolysaccharides, cyclic AMP receptor protein, Sigma factor RpoE, and RNA chaperone protein Hfq. These factors play crucial roles in bacterial colonization, invasion, evasion of host immune responses, biofilm formation, and urinary stone formation. This paper is the first to comprehensively describe the hydrogenase system, autotransporter proteins, molybdate-binding protein ModA, and two-component systems as virulence factors in Proteus mirabilis, providing new insights into its pathogenic mechanisms in urinary tract infections. This review explores the mechanisms of biofilm formation by Proteus mirabilis and the various virulence factors involved in UTIs, revealing many newly discovered virulence factors from recent studies. These findings may offer new targets for clinical treatment of UTIs and vaccine development, highlighting the importance of understanding these virulence factors.

The Assembly of the Inverse Autotransporter Protein YeeJ is Driven by its C-terminal β-strand

Autotransporter proteins are bacterial outer membrane proteins that display passenger domains with various functions through a β-barrel shaped translocation domain. YeeJ is an autotransporter protein from E. coli MG1655. In contrast to most other autotransporter proteins, its passenger domain is located at the C-terminus of the translocation domain. Due to this inverted domain organization, YeeJ belongs to autotransporter proteins of type Ve. To investigate the assembly of YeeJ, the fluorescence of a heterologous mCherry passenger domain was measured to quantify its assembly. Based on AlphaFold2 models of 119 sequences similar to YeeJ, a sequence conservation logo for the β1- and the β12-strand of type Ve autotransporter proteins was generated. Then, the effect of mutations in these strands on the assembly of YeeJ were analyzed. Mutations of the N-terminal aromatic amino acid of the β1-strand did not affect the assembly of the translocation domain and the display of the passenger domain. Likewise, exchange of the β1-strand with the β3-strand did not impair the assembly of the autotransporter fusion protein. Mutation of the C-terminal aromatic amino acid of the β12-strand strongly impaired surface display of the mCherry passenger domain. This amino acid has been shown before as an essential feature of the β-signals of classical autotransporter proteins and outer membrane β-barrel proteins in general. We therefore propose that the β12-strand of YeeJ acts as its β-signal and that the assembly of the YeeJ β-barrel is driven by its C-terminal β-strand, like in most other autotransporter proteins, despite its inverted domain organization.

Selection of vaccine candidates against Pseudomonas koreensis using reverse vaccinology and a preliminary efficacy trial in Empurau (Tor tambroides)

This study marks the first utilization of reverse vaccinology to develop recombinant subunit vaccines against Pseudomonas koreensis infection in Empurau (Tor tambroides). The proteome (5538 proteins) was screened against various filters to prioritize proteins based on features that are associated with virulence, subcellular localization, transmembrane helical structure, antigenicity, essentiality, non-homology with the host proteome, molecular weight, and stability, which led to the identification of eight potential vaccine candidates. These potential vaccine candidates were cloned and expressed, with six achieving successful expression and purification. The antigens were formulated into two distinct vaccine mixtures, Vac A and Vac B, and their protective efficacy was assessed through in vivo challenge experiments. Vac A and Vac B demonstrated high protective efficacies of 100 % and 81.2 %, respectively. Histological analyses revealed reduced tissue damage in vaccinated fish after experimental infection, with Vac A showing no adverse effects, whereas Vac B exhibited mild degenerative changes. Quantitative real-time PCR results showed a significant upregulation of TNF-α and downregulation of IL-1β in the kidneys, spleen, gills, and intestine in both Vac A- and Vac B-immunized fish after challenged with P. koreensis. Additionally, IL-8 exhibits tissue-specific differential expression, with significant upregulation in the kidney, gills, and intestine, and downregulation in the spleen, particularly notable in Vac A-immunized fish. The research underscores the effectiveness of the reverse vaccinology approach in fish and demonstrates the promising potential of Vac A and Vac B as recombinant subunit vaccines.

Gastrointestinal signals in supplemented media reveal a role in adherence for the Shigella flexneri sap autotransporter gene

Shigella flexneri causes severe diarrheal disease worldwide. While many aspects of pathogenesis have been elucidated, significant knowledge gaps remain regarding the role of putative chromosomally-encoded virulence genes. The uncharacterized sap gene encoded on the chromosome has significant nucleotide sequence identity to the fluffy (flu) antigen 43 autotransporter gene in pathogenic Escherichia coli. Here, we constructed a Δsap mutant in S. flexneri strain 2457T and examined the effects of this mutation on bacterial cell aggregation, biofilm formation, and adherence to colonic epithelial cells. Analyses included the use of growth media supplemented with glucose and bile salts to replicate small intestinal signals encountered by S. flexneri. Deletion of the sap gene in 2457T affected epithelial cell adherence, resulted in quicker bacterial cell aggregation, but did not affect biofilm formation. This work highlights a functional role for the sap gene in S. flexneri pathogenesis and further demonstrates the importance of using relevant and appropriate gastrointestinal signals to characterize virulence genes of enteropathogenic bacteria.

The Love and Hate Relationship between T5SS and Other Secretion Systems in Bacteria

Bacteria have existed on Earth for billions of years, exhibiting ubiquity and involvement in various biological activities. To ensure survival, bacteria usually release and secrete effector proteins to acquire nutrients and compete with other microorganisms for living space during long-term evolution. Consequently, bacteria have developed a range of secretion systems, which are complex macromolecular transport machines responsible for transporting proteins across the bacterial cell membranes. Among them, one particular secretion system that stands out from the rest is the type V secretion system (T5SS), known as the "autotransporter". Bacterial activities mediated by T5SS include adherence to host cells or the extracellular matrix, invasion of host cells, immune evasion and serum resistance, contact-dependent growth inhibition, cytotoxicity, intracellular flow, protease activity, autoaggregation, and biofilm formation. In a bacterial body, it is not enough to rely on T5SS alone; in most cases, T5SS cooperates with other secretion systems to carry out bacterial life activities, but regardless of how good the relationship is, there is friction between the secretion systems. T5SS and T1SS/T2SS/T3SS/T6SS all play a synergistic role in the pathogenic processes of bacteria, such as nutrient acquisition, pathogenicity enhancement, and immune modulation, but T5SS indirectly inhibits the function of T4SS. This could be considered a love-hate relationship between secretion systems. This paper uses the systematic literature review methodology to review 117 journal articles published within the period from 1995 to 2024, which are all available from the PubMed, Web of Science, and Scopus databases and aim to elucidate the link between T5SS and other secretion systems, providing clues for future prevention and control of bacterial diseases.

Interactive effects of Pseudomonas entomophila strain 23S and Clavibacter michiganensis subsp. michiganensis on proteome and anti-Cmm compound production

Pseudomonas entomophila strain 23S is an effective biocontrol bacterium for tomato bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm); it produces an inhibitory compound affecting the growth of Cmm. In this study, the interactions between pure cultures of P. entomophila 23S and Cmm were investigated. First, the population dynamics of each bacterium during the interaction was determined using the selective media. Second, the amount of anti-Cmm compound produced by P. entomophila 23S in the presence of Cmm was quantified using HPLC. Lastly, a label-free shotgun proteomics study of P. entomophila 23S, Cmm, and a co-culture was conducted to understand the effects of the interaction of each bacterium at the proteomic level. Compared with the pure culture grown, the total number of proteins decreased in the interaction for both bacteria. P. entomophila 23S secreted stress-related proteins, such as chaperonins, peptidases, ABC-transporters and elongation factors. The bacterium also produced more proteins related with purine, pyrimidine, carbon and nitrogen metabolisms in the presence of Cmm. The population enumeration study revealed that the Cmm population declined dramatically during the interaction, while the population of P. entomophila 23S maintained. The quantification of anti-Cmm compound indicated that P. entomophila 23S produced significantly higher amount of anti-Cmm compound when it was cultured with Cmm. Overall, the study suggested that P. entomophila 23S, although is cidal to Cmm, was also negatively affected by the presence of Cmm, while trying to adapt to the stress condition, and that such an environment favored increased production of the anti-Cmm compound by P. entomophila 23S. SIGNIFICANCE: Pseudomonas entomophila strain 23S is an effective biocontrol bacterium for tomato bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm); it produces an inhibitory compound affecting the growth of Cmm. In this study, secreted proteome of pure cultures of P. entomophila 23S and Cmm, and also of a co-culture was first time identified. Furthermore, the study found that P. entomophila strain 23S produced significantly higher amount of anti-Cmm compound when the bacterium was grown together with Cmm. Co-culture enhancing anti-Cmm compound production by P. entomophila 23S is useful information, particularly from a commercial point of view of biocontrol application, and for scale-up of anti-Cmm compound production.

Genomic evidence and virulence properties decipher the extra-host origin of Bordetella bronchiseptica

Until recently, members of the classical Bordetella species comprised only pathogenic bacteria that were thought to live exclusively in warm-blooded animals. The close phylogenetic relationship of Bordetella with Achromobacter and Alcaligenes, which include primarily environmental bacteria, suggests that the ancestral Bordetellae were probably free-living. Eventually, the Bordetella species evolved to infect and live within warm-blooded animals. The modern history of pathogens related to the genus Bordetella started towards the end of the 19th century when it was discovered in the infected respiratory epithelium of mammals, including humans. The first identified member was Bordetella pertussis, which causes whooping cough, a fatal disease in young children. In due course, B. bronchiseptica was recovered from the trachea and bronchi of dogs with distemper. Later, a second closely related human pathogen, B. parapertussis, was described as causing milder whooping cough. The classical Bordetellae are strictly host-associated pathogens transmitted via the host-to-host aerosol route. Recently, the B. bronchiseptica strain HT200 has been reported from a thermal spring exhibiting unique genomic features that were not previously observed in clinical strains. Therefore, it advocates that members of classical Bordetella species have evolved from environmental sources. This organism can be transmitted via environmental reservoirs as it can survive nutrient-limiting conditions and possesses a motile flagellum. This study aims to review the molecular basis of origin and virulence properties of obligate host-restricted and environmental strains of classical Bordetella.

Identification of an autotransporter peptidase of Rickettsia rickettsii responsible for maturation of surface exposed autotransporters

Members of the spotted fever group rickettsia express four large, surface-exposed autotransporters, at least one of which is a known virulence determinant. Autotransporter translocation to the bacterial outer surface, also known as type V secretion, involves formation of a β-barrel autotransporter domain in the periplasm that inserts into the outer membrane to form a pore through which the N-terminal passenger domain is passed and exposed on the outer surface. Two major surface antigens of Rickettsia rickettsii, are known to be surface exposed and the passenger domain cleaved from the autotransporter domain. A highly passaged strain of R. rickettsii, Iowa, fails to cleave these autotransporters and is avirulent. We have identified a putative peptidase, truncated in the Iowa strain, that when reconstituted into Iowa restores appropriate processing of the autotransporters as well as restoring a modest degree of virulence.

Bordetella pertussis and outer membrane vesicles

Bordetella pertussis is the causative agent of a respiratory infection called pertussis (whooping cough) that can be fatal in newborns and infants. The pathogen produces a variety of antigenic compounds which alone or simultaneously can damage various host cells. Despite the availability of pertussis vaccines and high vaccination coverage around the world, a resurgence of the disease has been observed in many countries. Reasons for the increase in pertussis cases may include increased awareness, improved diagnostic techniques, low vaccine efficacy, especially acellular vaccines, and waning immunity. Many efforts have been made to develop more effective strategies to fight against B. pertussis and one of the strategies is the use of outer membrane vesicles (OMVs) in vaccine formulations. OMVs are attracting great interest as vaccine platforms since they can carry immunogenic structures such as toxins and LPS. Many studies have been carried out with OMVs from different B. pertussis strains and they revealed promising results in the animal challenge and human preclinical model. However, the composition of OMVs differs in terms of isolation and purification methods, strains, culture, and stress conditions. Although the vesicles from B. pertussis represent an attractive pertussis vaccine candidate, further studies are needed to advance clinical research for next-generation pertussis vaccines. This review summarizes general information about pertussis, the history of vaccines against the disease, and the immune response to these vaccines, with a focus on OMVs. We discuss progress in developing an OMV-based pertussis vaccine platform and highlight successful applications as well as potential challenges and gaps.

Phylogenetic survey of the subtilase family and a data-mining-based search for new subtilisins from Bacillaceae

The subtilase family (S8), a member of the clan SB of serine proteases are ubiquitous in all kingdoms of life and fulfil different physiological functions. Subtilases are divided in several groups and especially subtilisins are of interest as they are used in various industrial sectors. Therefore, we searched for new subtilisin sequences of the family Bacillaceae using a data mining approach. The obtained 1,400 sequences were phylogenetically classified in the context of the subtilase family. This required an updated comprehensive overview of the different groups within this family. To fill this gap, we conducted a phylogenetic survey of the S8 family with characterised holotypes derived from the MEROPS database. The analysis revealed the presence of eight previously uncharacterised groups and 13 subgroups within the S8 family. The sequences that emerged from the data mining with the set filter parameters were mainly assigned to the subtilisin subgroups of true subtilisins, high-alkaline subtilisins, and phylogenetically intermediate subtilisins and represent an excellent source for new subtilisin candidates.

Third Generation Genome Sequencing Reveals That Endobacteria in Nematophagous Fungi Esteya vermicola Contain Multiple Genes Encoding for Nematicidal Proteins

Esteya vermicola is the first recorded endoparasitic nematophagous fungus with high infectivity capacity, attacking the pinewood nematode Bursaphelenchus xylophilus which causes pine wilt disease. Endosymbionts are found in the cytoplasm of E. vermicola from various geographical areas. We sequenced the genome of endobacteria residing in E. vermicola to discover possible biological functions of these widespread endobacteria. Multilocus phylogenetic analyses showed that the endobacteria form a previously unidentified lineage sister to Phyllobacterium myrsinacearum species. The number of genes in the endobacterium was 4542, with 87.8% of the proteins having a known function. It contained a high proportion of repetitive sequences, as well as more Acyl-CoA synthetase genes and genes encoding the electron transport chain, compared with compared with plant-associated P. zundukense Tri 48 and P. myrsinacearum DSM 5893. Thus, this symbiotic bacterium is likely to be more efficient in regulating gene expression and energy release. Furthermore, the endobacteria in nematophagous fungi Esteya vermicola contained multiple nematicidal subtilase/subtilisin encoding genes, so it is likely that endobacteria cooperate with the host to kill nematodes.

Comprehensive pan-genomic, resistome and virulome analysis of clinical OXA-48 producing carbapenem-resistant Serratia marcescens strains

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) have been thoroughly studied as the pathogens associated with hospital acquired infections. However, data on Serratia marcescens are not enough. S. marcescens is now becoming a propensity for its highly antimicrobial-resistant clinical infections.

METHODS

Four carbapenem-resistant S. marcescens (CR-SM) isolates were obtained from hospitalized patients through routine microbiological experiments. We assembled the isolates genomes using whole genome sequencing (WGS) and compared their resistome and virulome patterns.

RESULTS

The average length and CG content of chromosomes was 5.33 Mbp and 59.8%, respectively. The number of coding sequences (CDSs) ranged from 4,959 to 4,989. All strains had one single putative conjugative plasmid with IncL incompatibility (Inc) group. The strains harbored bla_CTX-M-15, bla_TEM-1 and bla_SHV-134. All plamsids were positive for bla_OXA-48. No bla_NDM-1, bla_KPC, bla_VIM and bla_IMP were identified. The bla_SRT-2 and aac(6')-Ic genes were chromosomally-encoded. Class 1 integron was detected in strains P8, P11 and P14. The Escher_RCS47 and Salmon_SJ46 prophages played major role in plasmid-mediated carraige of extended spectrum β-lactamases (ESBLs). The CR-SM strains were equipt with typical virulence factors of oppotunistic pathogens including biofilm formation, adhesins, secretory systems and siderophores. The strains did not have ability to produce prodigiosin but were positive for chitinase and EstA.

CONCLUSION

The presence of conjugative plasmids harboring major β-lactamases within prophage and class 1 integron structures highlights the role of different mobile genetic elements (MGEs) in distribution of AMR factors and more specifically carbapenemases. More molecular studies are required to determine the status of carbapenem resistance in clinical starins. However, appropriate strategies to control the global dissemination of CR-SM are urgent.

Secreted Autotransporter Toxin (Sat) Mediates Innate Immune System Evasion

Several strategies are used by Escherichia coli to evade the host innate immune system in the blood, such as the cleavage of complement system proteins by secreted proteases. Members of the Serine Proteases Autotransporters of Enterobacteriaceae (SPATE) family have been described as presenting proteolytic effects against complement proteins. Among the SPATE-encoding genes sat (secreted autotransporter toxin) has been detected in high frequencies among strains of E. coli isolated from bacteremia. Sat has been characterized for its cytotoxic action, but the possible immunomodulatory effects of Sat have not been investigated. Therefore, this study aimed to evaluate the proteolytic effects of Sat on complement proteins and the role in pathogenesis of BSI caused by extraintestinal E. coli (ExPEC). E. coli EC071 was selected as a Sat-producing ExPEC strain. Whole-genome sequencing showed that sat sequences of EC071 and uropathogenic E. coli CFT073 present 99% identity. EC071 was shown to be resistant to the bactericidal activity of normal human serum (NHS). Purified native Sat was used in proteolytic assays with proteins of the complement system and, except for C1q, all tested substrates were cleaved by Sat in a dose and time-dependent manner. Moreover, E. coli DH5α survived in NHS pre-incubated with Sat. EC071-derivative strains harboring sat knockout and in trans complementations producing either active or non-active Sat were tested in a murine sepsis model. Lethality was reduced by 50% when mice were inoculated with the sat mutant strain. The complemented strain producing active Sat partially restored the effect caused by the wild-type strain. The results presented in this study show that Sat presents immunomodulatory effects by cleaving several proteins of the three complement system pathways. Therefore, Sat plays an important role in the establishment of bloodstream infections and sepsis.

Multiple bacterial virulence factors focused on adherence and biofilm formation associate with outcomes in cirrhosis

BACKGROUND & AIMS

Altered gut microbiota is associated with poor outcomes in cirrhosis, including infections and hepatic encephalopathy (HE). However, the role of bacterial virulence factors (VFs) is unclear. Aim: Define association of VFs with cirrhosis severity and infections, their linkage with outcomes, and impact of fecal microbiota transplant (FMT).

METHODS

VF abundances were determined using metagenomic analysis in stools from controls and cirrhosis patients (compensated, HE-only, ascites-only, both and infected). Patients were followed for 90-day hospitalizations and 1-year death. Stool samples collected before/after a placebo-controlled FMT trial were also analyzed. Bacterial species and VFs for all species and selected pathogens (Escherichia, Klebsiella, Pseudomonas, Staphylococcus, Streptococcus, and Enterococcus spp) were compared between groups. Multi-variable analyses were performed for clinical biomarkers and VFs for outcome prediction. Changes in VFs pre/post-FMT and post-FMT/placebo were analyzed. Results: We included 233 subjects (40 controls, 43 compensated, 30 HE-only, 20 ascites-only, 70 both, and 30 infected). Decompensated patients, especially those with infections, had higher VFs coding for siderophores, biofilms, and adhesion factors versus the rest. Biofilm and adhesion VFs from Enterobacteriaceae and Enterococcus spp associated with death and hospitalizations independent of clinical factors regardless of when all VFs or selected pathogens were analyzed. FMT was associated with reduced VF post-FMT versus pre-FMT and post-placebo groups.

CONCLUSIONS

Virulence factors from multiple species focused on adhesion and biofilms increased with decompensation and infections, associated with death and hospitalizations independent of clinical factors, and were attenuated with FMT. Strategies focused on targeting multiple virulence factors could potentially impact outcomes in cirrhosis.

PRESENTATIONS

Portions of this manuscript were an oral presentation in the virtual International Liver Congress 2021.

ABBREVIATIONS

VF: virulence factors, HE: hepatic encephalopathy, FMT: Fecal microbiota transplant, PPI: proton pump inhibitors, LPS: lipopolysaccharides, VFDB: Virulence factor database, OTU: operational taxonomic units, SBP: spontaneous bacterial peritonitis, UTI: urinary tract infections, MRSA: methicillin resistant Staphylococcus aureus, VRE: vancomycin-resistant Enterococcus, MAAsLin2: Microbiome Multivariable Associations with Linear Models, LPS: lipopolysaccharides, AKI: acute kidney injury.

Immunoglobulin-fold containing bacterial adhesins: molecular and structural perspectives in host tissue colonization and infection

Immunoglobulin (Ig) domains are one of the most widespread protein domains encoded by the human genome and are present in a large array of proteins with diverse biological functions. These Ig domains possess a central structure, the immunoglobulin-fold, which is a sandwich of two β sheets, each made up of anti-parallel β strands, surrounding a central hydrophobic core. Apart from humans, proteins containing Ig-like domains are also distributed in a vast selection of organisms including vertebrates, invertebrates, plants, viruses and bacteria where they execute a wide array of discrete cellular functions. In this review, we have described the key structural deviations of bacterial Ig-folds when compared to the classical eukaryotic Ig-fold. Further, we have comprehensively grouped all the Ig-domain containing adhesins present in both Gram-negative and Gram-positive bacteria. Additionally, we describe the role of these particular adhesins in host tissue attachment, colonization and subsequent infection by both pathogenic and non-pathogenic Escherichia coli as well as other bacterial species. The structural properties of these Ig-domain containing adhesins, along with their interactions with specific Ig-like and non Ig-like binding partners present on the host cell surface have been discussed in detail.

An Inducible Expression System for Recombinant Sca Proteins with an Autotransporter Domain from Orientia Tsutsugamushi in Escherichia coli

BACKGROUND

Orientia tsutsugamushi (Ot) is an obligate, intracellular, gram-negative bacterium causing scrub typhus. Some of its encoded proteins play key roles in the adhesion and internalization of the Ot strain into host cells and are suitable resources for vaccine development and tools for scrub typhus diagnosis. Surface cell antigen (Sca) proteins, classified as autotransporter (AT) proteins, are one of the largest protein families involved in bacterial pathogenesis and can be promising candidates for vaccine development. These proteins are typically large and contain inhibitory domains; therefore, recombinant proteins without such domains have been evaluated for this purpose. However, the expression for recombinant Sca proteins containing the AT domain, which might largely affect their protective role against scrub typhus, has not been analyzed and optimized.

OBJECTIVE

In this study, we optimized expression and purification conditions for individual Ot Sca protein fragments [ScaA (27-1461), ScaC (257-526), ScaD (26-998), and ScaE (35-760)] harboring the AT domain.

METHODS

To this end, we subcloned sequences of codon-optimized DNA encoding Sca protein fragments into the Escherichia coli expression vector. In addition, the expression condition for individual Sca fragments was optimized, and the proteins were purified using one-step Ni-NTA column method. The purified fractions were re-folded by serial dilution method, followed by BCA quantification and densitometric analysis to estimate the yield and purity of proteins.

RESULTS

We prepared platforms for expression of recombinant Sca protein fragments [ScaA (27-1461), ScaC (257-526), ScaD (26-998), and ScaE (35-760)] containing an AT domain without the signal peptide and transmembrane (TM) domain. The protein yield per liter of culture with >70% of purity was ScaC (257-576), ScaE (35-760), ScaD (26-998), and ScaA (27-1461) in order.

CONCLUSION

Our results could be used to develop Sca AT-domain based vaccines and tools for scrub typhus diagnosis with rapid and cost-effective ways.

IgA1 Protease as a Vaccine Basis for Prevention of Bacterial Meningitis

Abstract

The review covers the study of the protective properties of IgA1 protease and the possibility of creating a vaccine preparation for the prevention of bacterial meningitis of various origins on its basis. Bacterial meningitis belongs to the group of socially dangerous diseases and is characterized by a severe course, numerous complications and high mortality. The approaches used at present in world practice to create antimicrobial vaccines are based on a narrow targeting against a specific pathogen. The development of a monocomponent vaccine against a wide range of bacterial pathogens with a common virulence factor is still relevant. IgA1 protease, a protein that is one of the main virulence factors of a number of gram-negative and gram-positive bacteria, can serve as such an antigen. Bacterial IgA1 protease is uniquely specific for immunoglobulins A1 (IgA1), cleaving peptide bonds in the hinge regions of the IgA1 in humans and other higher primates. Bacteria, getting on the mucous membrane, destroy IgA1, which acts as the first barrier to protect the body from infections. Neutralization of IgA1 protease at this stage can become an obstacle to the development of infection, hindering the adhesion of a number of pathogens that produce this protein. The data available in the literature on the mechanism of antibacterial protection are scattered and ambiguous. The review considers the literature data and the results of our own experiments on the protective activity of IgA1 protease. We have shown that the recombinant meningococcal IgA1 protease and some of its fragments protect mice from infection with a live virulent culture not only of meningococci of the main epidemic serogroups (A, B, C, and W135), but also of some of the most common virulent pneumococcal serotypes. The data obtained indicate the possibility of creating a monocomponent vaccine against these and, possibly, other bacterial infections. Currently, significant progress has been made in studying the structure and functions of secreted proteins in the bacteria Neisseria meningitidis and Haemophilus influenzae. In this review we describe protein translocation systems of N. meningitidis, which are related to the secretion of proteins in these bacteria, and also present modern data on the functions of these proteins. Analysis of experimental data on the structure of IgA1 protease of N. meningitidis and the formation of immunity during vaccination is of key importance in the development of prophylactic preparations.

Immunization with recombinant protein Ag43::UpaH with alum and 1,25(OH)2D3 adjuvants significantly protects Balb/C mice against urinary tract infection caused by uropathogenic Escherichia coli

The majority of urinary tract infections (UTIs) are caused by uropathogenic Escherichia coli (UPEC). Designing a vaccine will certainly reduce the occurrence of infection and antibiotic resistance of the isolates. Antigen 43 (Ag43) and autotransporter H (UpaH) have been associated with the virulence of UPEC. In the present study, the efficacy of different formulations of a hybrid protein composed of Ag43 and UpaH with and without alum and 1,25(OH)2D3 (Vitamin D3) adjuvants were evaluated in mice model. A significant increase in IgG and cellular responses was developed against Ag43::UpaH as compared to the control mice. The addition of alum or a mixture of alum and Vitamin D3 to the protein significantly enhanced the serum IgG responses and tended to remain in a steady state until 6 months. In addition, the mentioned formulations produced significant amounts of IgG1, IL-4, and IL-17 as compared to the fusion protein alone. In addition to the mentioned formulations, the combination of protein with Vitamin D3 also resulted in significantly higher serum IgA and IFN-γ levels as compared to the fusion protein alone. Mice immunized with fusion plus alum and formulation protein admixed with both alum and Vitamin D3 significantly reduced the bacterial load in the bladders and kidneys of mice as compared to the control. In this study, for the first time, the ability of a novel hybrid protein in combination with adjuvants alum and Vitamin D3 was evaluated against UPEC. Our results indicated that fusion Ag43::UpaH admixed with alum and Vitamin D3 could be a promising candidate against UTIs.

The Orientia tsutsugamushi ScaB Autotransporter Protein Is Required for Adhesion and Invasion of Mammalian Cells

Autotransporter proteins are widely present in Gram-negative bacteria. They play a pivotal role in processes related to bacterial pathogenesis, including adhesion, invasion, colonization, biofilm formation, and cellular toxicity. Bioinformatics analysis revealed that Orientia tsutsugamushi, the causative agent of scrub typhus, encodes six different autotransporter genes (scaA-scaF). Although four of these genes (scaA, scaC, scaD, and scaE) are present in diverse strains, scaB and scaF have been detected in only a limited number of strains. Previous studies have demonstrated that ScaA and ScaC are involved in the adherence of host cells. However, the putative function of other O. tsutsugamushi Sca proteins has not been studied yet. In this study, we show that scaB is transcribed and expressed on the surface of O. tsutsugamushi Boryong strain. Using a heterologous Escherichia coli expression system, we demonstrated that ScaB-expressing E. coli can successfully mediate adherence to and invasion into non-phagocytic cells, including epithelial and endothelial cells. In addition, pretreatment with a recombinant ScaB polypeptide inhibits the entry of O. tsutsugamushi into cultured mammalian cells. Finally, we also identified the scaB gene in the Kuroki and TA686 strains and observed high levels of sequence variation in the passenger domains. Here, we propose that the ScaB protein of O. tsutsugamushi can mediate both adhesion to and invasion into host cells in the absence of other O. tsutsugamushi genes and may play important roles in bacterial pathogenesis.

The Translocation and Assembly Module (TAM) of Edwardsiella tarda Is Essential for Stress Resistance and Host Infection

Translocation and assembly module (TAM) is a protein channel known to mediate the secretion of virulence factors during pathogen infection. Edwardsiella tarda is a Gram-negative bacterium that is pathogenic to a wide range of farmed fish and other hosts including humans. In this study, we examined the function of the two components of the TAM, TamA and TamB, of E. tarda (named tamA_Et and tamB_Et, respectively). TamA_Et was found to localize on the surface of E. tarda and be recognizable by TamA_Et antibody. Compared to the wild type, the tamA and tamB knockouts, TX01ΔtamA and TX01ΔtamB, respectively, were significantly reduced in motility, flagella formation, invasion into host cells, intracellular replication, dissemination in host tissues, and inducing host mortality. The lost virulence capacities of TX01ΔtamA and TX01ΔtamB were restored by complementation with the tamA_Et and tamB_Et genes, respectively. Furthermore, TX01ΔtamA and TX01ΔtamB were significantly impaired in the ability to survive under low pH and oxidizing conditions, and were unable to maintain their internal pH balance and cellular structures in acidic environments, which led to increased susceptibility to lysozyme destruction. Taken together, these results indicate that TamA_Et and TamB_Et are essential for the virulence of E. tarda and required for E. tarda to survive under stress conditions.

The Vacuolating Autotransporter Toxin (Vat) of Escherichia coli Causes Cell Cytoskeleton Changes and Produces Non-lysosomal Vacuole Formation in Bladder Epithelial Cells

Urinary tract infections (UTIs) affect more than 150 million people, with a cost of over 3.5 billion dollars, each year. Escherichia coli is associated with 70–80% of UTIs. Uropathogenic E. coli (UPEC) has virulence factors including adhesins, siderophores, and toxins that damage host cells. Vacuolating autotransporter toxin (Vat) is a member of serine protease autotransporter proteins of Enterobacteriaceae (SPATEs) present in some uropathogenic E. coli (UPEC) strains. Vat has been identified in 20–36% of UPEC and is present in almost 68% of urosepsis isolates. However, the mechanism of action of Vat on host cells is not well-known. Thus, in this study the effect of Vat in a urothelium model of bladder cells was investigated. Several toxin concentrations were tested for different time periods, resulting in 15–47% of cellular damage as measured by the LDH assay. Vat induced vacuole formation on the urothelium model in a time-dependent manner. Vat treatment showed loss of the intercellular contacts on the bladder cell monolayer, observed by Scanning Electron Microscopy. This was also shown using antibodies against ZO-1 and occludin by immunofluorescence. Additionally, changes in permeability of the epithelial monolayer was demonstrated with a fluorescence-based permeability assay. Cellular damage was also evaluated by the identification of cytoskeletal changes produced by Vat. Thus, after Vat treatment, cells presented F-actin distribution changes and loss of stress fibers in comparison with control cells. Vat also modified tubulin, but it was not found to affect Arp3 distribution. In order to find the nature of the vacuoles generated by Vat, the Lysotracker deep red fluorescent dye for the detection of acidic organelles was used. Cells treated with Vat showed generation of some vacuoles without acidic content. An ex vivo experiment with mouse bladder exposed to Vat demonstrated loss of integrity of the urothelium. In conclusion, Vat induced cellular damage, vacuole formation, and urothelial barrier dysregulation of bladder epithelial cells. Further studies are needed to elucidate the role of these vacuoles induced by Vat and their relationship with the pathogenesis of urinary tract infection.

Multiple ways to kill bacteria via inhibiting novel cell wall or membrane targets

The rise of antibiotic-resistant infections has been well documented and the need for novel antibiotics cannot be overemphasized. US FDA approved antibiotics target only a small fraction of bacterial cell wall or membrane components, well-validated antimicrobial targets. In this review, we highlight small molecules that inhibit relatively unexplored cell wall and membrane targets. Some of these targets include teichoic acids-related proteins (DltA, LtaS, TarG and TarO), lipid II, Mur family enzymes, components of LPS assembly (MsbA, LptA, LptB and LptD), penicillin-binding protein 2a in methicillin-resistant Staphylococcus aureus, outer membrane protein transport (such as LepB and BamA) and lipoprotein transport components (LspA, LolC, LolD and LolE). Inhibitors of SecA, cell division protein, FtsZ and compounds that kill persister cells via membrane targeting are also covered.

The Rich Tapestry of Bacterial Protein Translocation Systems

The translocation of proteins across membranes is a fundamental cellular function. Bacteria have evolved a striking array of pathways for delivering proteins into or across cytoplasmic membranes and, when present, outer membranes. Translocated proteins can form part of the membrane landscape, reside in the periplasmic space situated between the inner and outer membranes of Gram-negative bacteria, deposit on the cell surface, or be released to the extracellular milieu or injected directly into target cells. One protein translocation system, the general secretory pathway, is conserved in all domains of life. A second, the twin-arginine translocation pathway, is also phylogenetically distributed among most bacteria and plant chloroplasts. While all cell types have evolved additional systems dedicated to the translocation of protein cargoes, the number of such systems in bacteria is now known to exceed nine. These dedicated protein translocation systems, which include the types 1 through 9 secretion systems (T1SSs-T9SSs), the chaperone-usher pathway, and type IV pilus system, are the subject of this review. Most of these systems were originally identified and have been extensively characterized in Gram-negative or diderm (two-membrane) species. It is now known that several of these systems also have been adapted to function in Gram-positive or monoderm (single-membrane) species, and at least one pathway is found only in monoderms. This review briefly summarizes the distinctive mechanistic and structural features of each dedicated pathway, as well as the shared properties, that together account for the broad biological diversity of protein translocation in bacteria.

Identification of Haemophilus parasuis genes uniquely expressed during infection using in vivo-induced antigen technology

Haemophilus parasuis is the etiological agent of Glässer's disease which is characterized by fibrinous polyserositis, arthritis and meningitis. The pathogenesis of this bacterium remains largely unknown. Genes expressed in vivo may play an important role in the pathogenicity of H. parasuis. The development of in vivo-induced antigen technology (IVIAT) has provided a valuable tool for the identification of in vivo-induced genes during bacterial infection. In this study, IVIAT was applied to identify in vivo-induced antigens of H. parasuis. Pooled swine H. parasuis-positive sera, adsorbed against in vitro-grown cultures of H. parasuis SH0165 and Escherichia coli BL21 (DE3), were used to screen the inducible expression library of genomic proteins from whole genome sequenced H. parsuis SH0165. Finally, 24 unique genes expressed in vivo were successfully identified after secondary and tertiary screening with IVIAT. These genes were implicated in cell surface proteins, metabolism, stress response, regulation, transportation and other processes. Quantitative real-time PCR showed that the mRNA levels of 24 genes were all upregulated in vivo relative to in vitro, with 13 genes were detected significantly upregulated in H. parasuis infected pigs. Several potential virulence-associated genes were found to be uniquely expressed in vivo, including espP, lnt, hutZ, mreC, vtaA, pilB, tex, sunT and aidA. The results indicated that the proteins identified using IVIAT may play important roles in the pathogenesis of H. parasuis infection in vivo.

BamA is required for autotransporter secretion

BACKGROUND

In Gram-negative bacteria, type Va and Vc autotransporters are proteins that contain both a secreted virulence factor (the "passenger" domain) and a β-barrel that aids its export. While it is known that the folding and insertion of the β-barrel domain utilize the β-barrel assembly machinery (BAM) complex, how the passenger domain is secreted and folded across the membrane remains to be determined. The hairpin model states that passenger domain secretion occurs independently through the fully-formed and membrane-inserted β-barrel domain via a hairpin folding intermediate. In contrast, the BamA-assisted model states that the passenger domain is secreted through a hybrid of BamA, the essential subunit of the BAM complex, and the β-barrel domain of the autotransporter.

METHODS

To ascertain the models' plausibility, we have used molecular dynamics to simulate passenger domain secretion for two autotransporters, EspP and YadA.

RESULTS

We observed that each protein's β-barrel is unable to accommodate the secreting passenger domain in a hairpin configuration without major structural distortions. Additionally, the force required for secretion through EspP's β-barrel is more than that through the BamA β-barrel.

CONCLUSIONS

Secretion of autotransporters most likely occurs through an incompletely formed β-barrel domain of the autotransporter in conjunction with BamA.

GENERAL SIGNIFICANCE

Secretion of virulence factors is a process used by practically all pathogenic Gram-negative bacteria. Understanding this process is a necessary step towards limiting their infectious capacity.

Chlamydia: what is on the outside does matter

This review summarises major highlights on the structural biology of the chlamydial envelope. Chlamydiae are obligate intracellular bacteria, characterised by a unique biphasic developmental cycle. Depending on the stage of their lifecycle, they appear in the form of elementary or reticulate bodies. Since these particles have distinctive functions, it is not surprising that their envelope differs in lipid as well as in protein content. Vice versa, by identifying surface proteins, specific characteristics of the particles such as rigidity or immunogenicity may be deduced. Detailed information on the bacterial membranes will increase our understanding on the host-pathogen interactions chlamydiae employ to survive and grow and might lead to new strategies to battle chlamydial infections.

Antimicrobial activity of endodontic sealers and medications containing chitosan and silver nanoparticles against Enterococcus faecalis

BACKGROUND

The main microorganism associated with the failure of endodontic treatments is Enterococcus faecalis. Although several endodontic therapeutics have demonstrated antimicrobial activity against E. faecalis, the antimicrobial effectiveness of chitosan (CsNPs) and silver nanoparticles (AgNPs) included into conventional endodontic sealers for endodontic therapies is still unclear.

AIM

The objective of this study was to evaluate the antibacterial activity increment (AAI) of endodontic sealers containing CsNPs and AgNPs as well as some chemical components against E. faecalis by direct contact assays.

METHODS

CsNPs and AgNPs were synthesized by reduction and ionic gelation methods, respectively. Nanoparticles were characterized by dynamic light scattering and energy dispersive X-ray analysis. The bactericidal activity was tested on monolayers on agar plates and collagen membrane surface assays against E. faecalis.

RESULTS

The size of CsNPs was 70.6±14.8 nm and zeta potential was 52.0±5.4 mV; the size of AgNPs was 54.2±8.5 nm, and zeta potential was -48.4±6.9 mV. All materials, single or combined, showed an AAI, especially when CsNPs, chlorhexidine (Chx), and the combination of CsNPs-Chx were added. However, the combination of CsNPs-Chx showed the highest (55%) AAI, followed by Chx (35.5%) and CsNPs (11.1%), respectively. There was a significant statistical difference in all comparisons (p < 0.05). Tubliseal (40%) and AH Plus (32%) sealants showed a higher AAI on E. faecalis in the monolayer test and collagen membrane assay analyzed by scanning electron microscopy.

CONCLUSIONS

Tubliseal and AH plus sealers combined with nanoparticles, especially CsNPs-Chx, could be used for conventional endodontic treatments in the control of E. faecalis bacteria.

Serine protease autotransporters of Enterobacteriaceae (SPATEs) are largely distributed among Escherichia coli isolated from the bloodstream

Extraintestinal pathogenic Escherichia coli (ExPEC) is the major cause of Gram-negative-related sepsis. Bacterial survival in the bloodstream is mediated by a variety of virulence traits, including those mediating immune system evasion. Serine protease autotransporters of Enterobacteriaceae (SPATE) constitute a superfamily of virulence factors that can cause tissue damage and cleavage of molecules of the complement system, which is a key feature for the establishment of infection in the bloodstream. In this study, we analyzed 278 E. coli strains isolated from human bacteremia from inpatients of both genders, different ages, and clinical conditions. These strains were screened for the presence of SPATE-encoding genes as well as for phylogenetic classification and intrinsic virulence of ExPEC. SPATE-encoding genes were detected in 61.2% of the strains and most of these strains (44.6%) presented distinct SPATE-encoding gene profiles. sat was the most frequent gene among the entire collection, found in 34.2%, followed by vat (28.4%), pic (8.3%), and tsh (4.7%). Although in low frequencies, espC (0.7%), eatA (1.1%), and espI (1.1%) were detected and are being reported for the first time in extraintestinal isolates. The presence of SPATE-encoding genes was positively associated to phylogroup B2 and intrinsic virulent strains. These findings suggest that SPATEs are highly prevalent and involved in diverse steps of the pathogenesis of bacteremia caused by E. coli.

Identification of Host Adaptation Genes in Extraintestinal Pathogenic Escherichia coli during Infection in Different Hosts

Extraintestinal pathogenic Escherichia coli (ExPEC) is an important human and animal pathogen. Despite the apparent similarities in their known virulence attributes, some ExPEC strains can cross the host species barrier and present a zoonotic potential, whereas other strains exhibit host specificity, suggesting the existence of unknown mechanisms that remain to be identified. We applied a transposon-directed insertion site sequencing (TraDIS) strategy to investigate the ExPEC XM strain, which is capable of crossing the host species barrier, and to screen for virulence-essential genes in both mammalian (mouse) and avian (duck) models of E. coli-related septicemia. We identified 151 genes essential for systemic infection in both mammalian and avian models, 97 required only in the mammalian model, and 280 required only in the avian model. Ten genes/gene clusters were selected for further validation, and their contributions to ExPEC virulence in both mammalian and avian models or mammalian- or avian-only models were confirmed by animal tests. This represents the first comprehensive genome-wide analysis of virulence-essential genes required for systemic infections in two different host species and provides a further comprehensive understanding of ExPEC-related virulence, host specificity, and adaptation.

A new role for host annexin A2 in establishing bacterial adhesion to vascular endothelial cells: lines of evidence from atomic force microscopy and an in vivo study

Understanding bacterial adhesion is challenging and critical to our understanding of the initial stages of the pathogenesis of endovascular bacterial infections. The vascular endothelial cell (EC) is the main target of Rickettsia, an obligately intracellular bacterium that causes serious systemic disease in humans and animals. But the mechanism(s) underlying bacterial adherence to ECs under shear stress from flowing blood prior to activation are unknown for any bacteria. Although host surface annexin a2 (ANXA2) has been identified to participate in efficient bacterial invasion of epithelial cells, direct evidence is lacking in the field of bacterial infections of ECs. In the present study, we employ a novel, anatomically based, in vivo quantitative bacterial-adhesion-to-vascular-EC system, combined with atomic force microscopy (AFM), to examine the role of endothelial luminal surface ANXA2 during rickettsial adherence to ECs. We also examined whether ANXA2 antibody affected binding of Staphylococcus aureus to ECs. We found that deletion of ANXA2 impeded rickettsial attachment to the ECs in vitro and blocked rickettsial adherence to the blood vessel luminal surface in vivo. The AFM studies established that EC surface ANXA2 acts as an adherence receptor for rickettsiae, and that rickettsial adhesin OmpB is the associated bacterial ligand. Furthermore, pretreatment of ECs with anti-ANXA2 antibody reduced EC surface-associated S. aureus. We conclude that the endothelial surface ANXA2 plays an important role in initiating pathogen-host interactions, ultimately leading to bacterial anchoring on the vascular luminal surface.

Chaperone OsmY facilitates the biogenesis of a major family of autotransporters

OsmY is a widely conserved but poorly understood 20 kDa periplasmic protein. Using a folding biosensor, we previously obtained evidence that OsmY has molecular chaperone activity. To discover natural OsmY substrates, we screened for proteins that are destabilized and thus present at lower steady-state levels in an osmY-null strain. The abundance of an outer membrane protein called antigen 43 was substantially decreased and its β-barrel domain was undetectable in the outer membrane of an osmY-null strain. Antigen 43 is a member of the diffuse adherence family of autotransporters. Like strains that are defective in antigen 43 production, osmY-null mutants failed to undergo cellular autoaggregation. In vitro, OsmY assisted in the refolding of the antigen 43 β-barrel domain and protected it from added protease. Finally, an osmY-null strain that expressed two members of the diffuse adherence family of autotransporters that are distantly related to antigen 43, EhaA and TibA, contained reduced levels of the proteins and failed to undergo cellular autoaggregation. Taken together, our results indicate that OsmY is involved in the biogenesis of a major subset of autotransporters, a group of proteins that play key roles in bacterial pathogenesis.

Countering Gram-Negative Antibiotic Resistance: Recent Progress in Disrupting the Outer Membrane with Novel Therapeutics

Gram-negative bacteria shield themselves from antibiotics by producing an outer membrane (OM) that forms a formidable permeability barrier. Multidrug resistance among these organisms is a particularly acute problem that is exacerbated by the OM. The poor penetrance of many available antibiotics prevents their clinical use, and efforts to discover novel classes of antibiotics against Gram-negative bacteria have been unsuccessful for almost 50 years. Recent insights into how the OM is built offer new hope. Several essential multiprotein molecular machines (Bam, Lpt, and Lol) work in concert to assemble the barrier and offer a swathe of new targets for novel therapeutic development. Murepavadin has been at the vanguard of these efforts, but its recently reported phase III clinical trial toxicity has tempered the anticipation of imminent new clinical options. Nonetheless, the many concerted efforts aimed at breaking down the OM barrier provide a source of ongoing optimism for what may soon come through the development pipeline. We will review the current state of drug development against the OM assembly targets, highlighting insightful new discovery approaches and strategies.

Autotransporter MisL of Salmonella enterica serotype Typhimurium facilitates bacterial aggregation and biofilm formation

Salmonella enterica serovar Typhimurium (S. Typhimurium) is an important food-borne zoonotic pathogen that causes increased morbidity and mortality worldwide. The autotransporter (AT) proteins are a large and diverse family of extracellular proteins, many of which contribute to the pathogenicity of Gram-negative bacteria. The S. Typhimurium AT protein MisL mediates intestinal colonization in mice. Bioinformatics analyses indicated that MisL clusters with ATs are involved in bacterial biofilm formation, aggregation and adherence. In this study, we found that the misL overexpression increased S. Typhimurium biofilm formation. In addition, the misL deletion reduced bacterial adherence and invasion abilities on HeLa cells, but did not affect the bacterial virulence. Similarly, MisL expression in Escherichia coli strain promoted bacterial biofilm formation as well as adhesion and invasion capacities. However, the misL overexpression had no influence on the bacterial aggregation except for AAEC189Δflu, a strain lacking type I fimbriae. Moreover, we demonstrated that immunization with recombinant MisL protein stimulated the production of high IgG antibody titers, which conferred modest protection against S. Typhimurium infection. This study illustrates the novel biological functions and immunoprotective effects of MisL in S. Typhimurium.

Inhibition of autotransporter biogenesis by small molecules

Disarming pathogens by targeting virulence factors is a promising alternative to classic antibiotics. Many virulence factors in Gram-negative bacteria are secreted via the autotransporter (AT) pathway, also known as Type 5 secretion. These factors are secreted with the assistance of two membrane-based protein complexes: Sec and Bam. To identify inhibitors of the AT pathway, we used transcriptomics analysis to develop a fluorescence-based high-throughput assay that reports on the stress induced by the model AT hemoglobin protease (Hbp) when its secretion across the outer membrane is inhibited. Screening a library of 1600 fragments yielded the compound VUF15259 that provokes cell envelope stress and secretion inhibition of the ATs Hbp and Antigen-43. VUF15259 also impairs β-barrel folding activity of various outer membrane proteins. Furthermore, we found that mutants that are compromised in outer membrane protein biogenesis are more susceptible to VUF15259. Finally, VUF15259 induces the release of vesicles that appear to assemble in short chains. Taken together, VUF15259 is the first reported compound that inhibits AT secretion and our data are mostly consistent with VUF15259 interfering with the Bam-complex as potential mode of action. The validation of the presented assay incites its use to screen larger compound libraries with drug-like compounds.

Biogenesis and function of the autotransporter adhesins YadA, intimin and invasin

Bacteria often express numerous virulence factors. These virulence factors make them successful pathogens, by e.g. mediating attachment to host cells and thereby facilitating persistence or invasion, or by contributing to the evasion of the host immune system to allow proliferation and spread within the host and in the environment. The site of first contact of Gram negative bacteria with the host is the bacterial outer membrane (OM). Consisting of an asymmetrical lipid bilayer with phospholipids forming the inner, and lipopolysaccharides forming the outer leaflet, the OM harbors numerous integral membrane proteins that are almost exclusively β-barrel proteins. One distinct family of OM β-barrel proteins strongly linked to bacterial virulence are the autotransporter (AT) proteins. During the last years huge progress has been made to better understand the mechanisms underlying the insertion of AT proteins into the OM and also AT function for interaction with the host. This review shortly summarizes our current knowledge about outer membrane protein (OMP) and more specifically AT biogenesis and function. We focused on the AT proteins that we haved studied in most detail: i.e. the Yersinia adhesin A (YadA) and invasin of Yersinia enterocolitica (Ye) as well as its homolog intimin (Int) expressed by enteropathogenic Escherichia coli. In addition, this review provides a short outlook about how we could possibly use this knowledge to fight infection.

Characterization of the non-glandular gastric region microbiota in Helicobacter suis-infected versus non-infected pigs identifies a potential role for Fusobacterium gastrosuis in gastric ulceration

Helicobacter suis has been associated with development of gastric ulcers in the non-glandular part of the porcine stomach, possibly by affecting gastric acid secretion and altering the gastric microbiota. Fusobacterium gastrosuis is highly abundant in the gastric microbiota of H. suis-infected pigs and it was hypothesized that this micro-organism could play a role in the development of gastric ulceration. The aim of this study was to obtain further insights in the influence of a naturally acquired H. suis infection on the microbiota of the non-glandular part of the porcine stomach and in the pathogenic potential of F. gastrosuis. Infection with H. suis influenced the relative abundance of several taxa at phylum, family, genus and species level. H. suis-infected pigs showed a significantly higher colonization rate of F. gastrosuis in the non-glandular gastric region compared to non-infected pigs. In vitro, viable F. gastrosuis strains as well as their lysate induced death of both gastric and oesophageal epithelial cell lines. These gastric cell death inducing bacterial components were heat-labile. Genomic analysis revealed that genes are present in the F. gastrosuis genome with sequence similarity to genes described in other Fusobacterium spp. that encode factors involved in adhesion, invasion and induction of cell death as well as in immune evasion. We hypothesize that, in a gastric environment altered by H. suis, colonization and invasion of the non-glandular porcine stomach region and production of epithelial cell death inducing metabolites by F. gastrosuis, play a role in gastric ulceration.

Protective potency of recombinant meningococcal IgA1 protease and its structural derivatives upon animal invasion with meningococcal and pneumococcal infections

Immunization of mice with recombinant IgA1 protease of Neisseria meningitidis or several structural derivatives thereof protects the animals infected with a variety of deadly pathogens, including N. meningitidis serogroups A, B, and C and 3 serotypes of Streptococcus pneumonia. In sera of rabbits immunized with inactivated pneumococcal cultures, antibodies binding IgA1-protease from N. meningitidis serogroup B were detected. Thus, the cross-reactive protection against meningococcal and pneumococcal infections has been demonstrated in vivo. Presumably it indicates the presence of common epitopes in the N. meningitidis IgA1 protease and S. pneumoniae surface proteins.

Type V Secretion in Gram-Negative Bacteria

Type V, or "autotransporter," secretion is a term used to refer to several simple protein export pathways that are found in a wide range of Gram-negative bacteria. Autotransporters are generally single polypeptides that consist of an extracellular ("passenger") domain and a β barrel domain that anchors the protein to the outer membrane (OM). Although it was originally proposed that the passenger domain is secreted through a channel formed solely by the covalently linked β barrel domain, experiments performed primarily on the type Va, or "classical," autotransporter pathway have challenged this hypothesis. Several lines of evidence strongly suggest that both the secretion of the passenger domain and the membrane integration of the β barrel domain are catalyzed by the barrel assembly machinery (Bam) complex, a conserved hetero-oligomer that plays an essential role in the assembly of most integral OM proteins. The secretion reaction appears to be driven at least in part by the folding of the passenger domain in the extracellular space. Although many aspects of autotransporter biogenesis remain to be elucidated, it will be especially interesting to determine whether the different classes of proteins that fall under the type V rubric-most of which have not been examined in detail-are assembled by the same basic mechanism as classical autotransporters.

Proteomic characterization of outer membrane vesicles from gut mucosa-derived fusobacterium nucleatum

Fusobacterium nucleatum is a Gram-negative bacterium commonly found in the oral cavity and is often involved in periodontal diseases. Recent studies have shown increased F. nucleatum prevalence in colorectal cancer (CRC) tissues, and causal data has linked this bacterium to CRC tumorigenesis. Immune-based approaches to contain, reduce or eradicate its gut colonization may prevent CRC. Outer membrane vesicles (OMVs) are naturally produced by Gram-negative bacteria, typically contain multiple putative virulence factors and may elicit protective immune responses if used as vaccines. Here, OMVs were isolated from F. nucleatum cultures and purified using gradient centrifugation. Proteins contained within the OMVs were identified by nano LC/MS/MS analysis. Of 98 proteins consistently identified from duplicate analyses, 60 were predicted to localize to the outer membrane or periplasm via signal peptide driven translocation. Of these, six autotransporter proteins, which constitute the majority of protein mass of OMVs, were associated with Type V secretion system. In addition, other putative virulence factor proteins with functional domains, including FadA, MORN2 and YadA-like domain, were identified with multiple exposed epitope sites as determined by in silico analysis. Altogether, the non-replicative OMVs of F. nucleatum contain multiple antigenic virulence factors that may play important roles in the design and development of vaccines against F. nucleatum. SIGNIFICANCE: Fusobacterium nulceatum has been proved playing significant role in colorectal carcinogenesis. Outer membrane vesicles are nanoparticles that naturally secreted by Gram-negative bacterial containing various antigenic components, which provides new insight in vaccine development. Understanding the constituents of F. nucleatum OMVs will provide fundamental information and potential strategies for OMV-based F. nucleatum vaccines design. Based on our knowledge this is the first proteomic study of OMVs from F. nucleatum.

A Nonfimbrial Adhesin of Aggregatibacter actinomycetemcomitans Mediates Biofilm Biogenesis

Periodontitis is an inflammatory disease caused by polymicrobial biofilms. The periodontal pathogen Aggregatibacter actinomycetemcomitans displays two proteinaceous surface structures, the fimbriae and the nonfimbrial extracellular matrix binding protein A (EmaA), as observed by electron microscopy. Fimbriae participate in biofilm biogenesis and the EmaA adhesins mediate collagen binding. However, in the absence of fimbriae, A. actinomycetemcomitans still retains the potential to form robust biofilms, suggesting that other surface macromolecules participate in biofilm development. Here, isogenic mutant strains lacking EmaA structures, but still expressing fimbriae, were observed to have reduced biofilm potential. In strains lacking both EmaA and fimbriae, biofilm mass was reduced by 80%. EmaA enhanced biofilm formation in different strains, independent of the fimbriation state or serotype. Confocal microscopy revealed differences in cell density within microcolonies between the EmaA positive and mutant strains. EmaA-mediated biofilm formation was found to be independent of the glycosylation state and the precise three-dimensional conformation of the protein, and thus this function is uncorrelated with collagen binding activity. The data suggest that EmaA is a multifunctional adhesin that utilizes different mechanisms to enhance bacterial binding to collagen and to enhance biofilm formation, both of which are important for A. actinomycetemcomitans colonization and subsequent infection.

Proteomics, Bioinformatics and Structure-Function Antigen Mining For Gonorrhea Vaccines

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the serious health consequences combined with the prevalence and the dire possibility of untreatable gonorrhea. Reverse vaccinology, which includes genome and proteome mining, has proven successful in the discovery of vaccine candidates against many pathogenic bacteria. Here, we describe proteomic applications including comprehensive, quantitative proteomic platforms and immunoproteomics coupled with broad-ranging bioinformatics that have been applied for antigen mining to develop gonorrhea vaccine(s). We further focus on outlining the vaccine candidate decision tree, describe the structure-function of novel proteome-derived antigens as well as ways to gain insights into their roles in the cell envelope, and underscore new lessons learned about the fascinating biology of Neisseria gonorrhoeae.

The Pulmonary Extracellular Matrix Is a Bactericidal Barrier Against Haemophilus influenzae in Chronic Obstructive Pulmonary Disease (COPD): Implications for an in vivo Innate Host Defense Function of Collagen VI

Non-typeable Haemophilus influenzae (NTHi) is a Gram-negative human commensal commonly residing in the nasopharynx of preschool children. It occasionally causes upper respiratory tract infection such as acute otitis media, but can also spread to the lower respiratory tract causing bronchitis and pneumonia. There is increasing recognition that NTHi has an important role in chronic lower respiratory tract inflammation, particularly in persistent infection in patients suffering from chronic obstructive pulmonary disease (COPD). Here, we set out to assess the innate protective effects of collagen VI, a ubiquitous extracellular matrix component, against NTHi infection in vivo. In vitro, collagen VI rapidly kills bacteria through pore formation and membrane rupture, followed by exudation of intracellular content. This effect is mediated by specific binding of the von Willebrand A (VWA) domains of collagen VI to the NTHi surface adhesins protein E (PE) and Haemophilus autotransporter protein (Hap). Similar observations were made in vivo specimens from murine airways and COPD patient biopsies. NTHi bacteria adhered to collagen fibrils in the airway mucosa and were rapidly killed by membrane destabilization. The significance in host-pathogen interplay of one of these molecules, PE, was highlighted by the observation that it confers partial protection from bacterial killing. Bacteria lacking PE were more prone to antimicrobial activity than NTHi expressing PE. Altogether the data shed new light on the carefully orchestrated molecular events of the host-pathogen interplay in COPD and emphasize the importance of the extracellular matrix as a novel branch of innate host defense.