Identification of oligopeptide-binding protein (OppA) and its role in the virulence of Streptococcus suis serotype 2

The ABC transporter Opp imports reduced glutathione, while Gsi imports glutathione disulfide in Escherichia coli

Glutathione is the major thiol-based antioxidant in a wide variety of biological systems, ranging from bacteria to eukaryotes. As a redox couple, consisting of reduced glutathione (GSH) and its oxidized form, glutathione disulfide (GSSG), it is crucial for the maintenance of the cellular redox balance. Glutathione transport out of and into cellular compartments and the extracellular space is a determinant of the thiol-disulfide redox state of the organelles and bodily fluids in question, but is currently not well understood. Here we use the genetically-encoded, glutathione-measuring redox probe Grx1-roGFP2 to comprehensively elucidate the import of extracellular glutathione into the cytoplasm of the model organism Escherichia coli. The elimination of only two ATP-Binding Cassette (ABC) transporter systems, Gsi and Opp, completely abrogates glutathione import into E. coli's cytoplasm, both in its reduced and oxidized form. The lack of only one of them, Gsi, completely prevents import of GSSG, while the lack of the other, Opp, substantially retards the uptake of reduced glutathione (GSH).

AcfA Regulates the Virulence and Cell Envelope Stress Response of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a ubiquitous inhabitant of estuarine and marine environments that causes vibriosis in aquatic animals and food poisoning in humans. Accessory colonizing factor (ACF) is employed by Vibrio to assist in the colonization and invasion of host cells leading to subsequent illnesses. In this work, ΔacfA, an in-frame deletion mutant strain lacking the 4th to the 645th nucleotides of the open reading frame (ORF) of the acfA gene, and the complementary strain acfA+ were constructed to decipher the function of AcfA in V. parahaemolyticus. The deletion of acfA had no effect on bacterial growth but resulted in a significant reduction in biofilm formation, hemolytic activity, mucus adhesion, and the accumulated mortality of zebrafish, compared to the wild-type strain and the complementary strain acfA+. Additionally, AcfA was involved in adapting to stressors, such as H2O2, EDTA, and acid, in V. parahaemolyticus. Furthermore, RNA-Seq transcriptome analysis was conducted to identify global gene transcription alterations resulting from deletion of the acfA gene. A total of 416 differentially expressed genes were identified in the ΔacfA vs. wild-type comparison, with 238 up-regulated genes and 178 down-regulated genes. The expression of genes associated with the type III secretion system, type VI secretion system, and oligopeptide permeases system were significantly reduced, and yet the expression of genes associated with cell envelope biosynthesis and response regulation system were enhanced dramatically in the absence of the acfA gene compared to the wild-type strain. These findings suggest that AcfA may play a role in the overall success of pathogenesis and the cell envelope stress response of V. parahaemolyticus.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

Increased heat tolerance and transcriptome analysis of Salmonella enterica Enteritidis PT 30 heat-shocked at 42 ℃

In this study, we compared the heat tolerance parameter (D_65℃) values of Salmonella enterica serovar Enteritidis PT 30 (S. Enteritidis ) heat adapted at different degrees (at 42 ℃ for 20-180 min) and cultivated using two methods. The treated group with the highest D_65℃ value (LP-42 ℃-60 min) and the untreated groups (Control-TSB and Control-TSA) were subjected to transcriptome analysis. Heat-adaptation increased the D_65℃ values of S. Enteritidis by 24.5-60.8%. The D_65℃ values of the LP-42 ℃-60 min group (1.85 ± 0.13 min, 7.7% higher) was comparable to that of the Control-TSA. A total of 483 up- and 443 downregulated genes of S. enteritidis were identified in the LP-42 ℃-60 min group (log₂fold change > 1, adjusted p-value < 0.05). Among these genes, 5 co-expressed and 15 differentially expressed genes in the LP-42 ℃-60 min and Control-TSA grops possibly contributed to the high D_65℃ values of S. Enteritidis . The Rpo regulon was involved in the heat adaptation of S. Enteritidis , as evidenced by the significant upregulation of rpoS, rpoN, and rpoE. KEGG enrichment pathways, such as biosynthesis of secondary metabolites, tricarboxylic acid, and ribosomes were identified and mapped to reveal the molecular mechanisms of S. enteritidis during heat adaptation. This study quantified the enhanced heat tolerance of S. Enteritidis heat adapted at different degrees of heat-adaptation. The results of this study may serve as a basis for elucidating the molecular mechanisms underlying the enhanced heat tolerance at the transcriptome level.

Phenotypic and Genomic Comparison of Staphylococcus aureus Highlight Virulence and Host Adaptation Favoring the Success of Epidemic Clones

Methicillin-resistant Staphylococcus aureus (MRSA) of the sequence type 59 (ST59) and ST398 lineages has emerged in hospitals and displayed a higher virulent potential than its counterparts ST5 and ST239. However, the mechanism of the host cell-pathogen interaction and specific determinates that contribute to the success of epidemic clones remain incompletely understood. In the present study, 142 S. aureus strains (ST59, ST398, ST239, and ST5) were selected from our 7-year national surveillance of S. aureus bloodstream infections (n = 983). We revealed that ST59 and ST398 had a higher prevalence of the protease-associated genes hysA^VSaβ, paiB, and cfim and enhanced proteolytic activity than the other lineages. ST59 and ST398 showed a higher expression of RNAIII and psmα and greater proficiency at causing cell lysis than other lineages. Furthermore, ST59 and ST398 were strongly recognized by human neutrophils and caused more cell apoptosis and neutrophil extracellular trap degradation than the other lineages. In addition, these strains differed substantially in their repertoire and composition of intact adhesion genes. Moreover, ST398 displayed higher adaptability to human epidermal keratinocytes and a unique genetic arrangement inside the oligopeptide ABC transport system, indicating functional variations. Overall, our study revealed some potential genomic traits associated with virulence and fitness that might account for the success of epidemic clones. IMPORTANCE Considerable efforts have been exerted to identify factors contributing to the success of epidemic Staphylococcus aureus clones, however, comparative phenotypic studies lack representation owing to the small number of strains. Large-scale strain collections focused on the description of genomic characteristics. Moreover, methicillin-resistant S. aureus infections constitute 30% to 40% of S. aureus bloodstream infections, and recent research has elucidated highly virulent methicillin-susceptible S. aureus strains. However, comprehensive research on the factors contributing to the success of epidemic S. aureus clones is lacking. In this study, 142 S. aureus strains were selected from our 7-year national surveillance of S. aureus bloodstream infections (n = 983) accompanied by a rigorous strain selection process. A combination of host cell-pathogen interactions and genomic analyses was applied to the represented strains. We revealed some potential genomic traits associated with virulence and fitness that might account for the success of epidemic clones.

Streptococcus suis TrpX is part of a tryptophan uptake system, and its expression is regulated by a T-box regulatory element

Streptococcus suis, a common member of the porcine respiratory microbiota, can cause life-threatening diseases in pigs as well as humans. A previous study identified the gene trpX as conditionally essential for in vivo survival by intrathecal infection of pigs with a transposon library of S. suis strain 10. Here, we characterized trpX, encoding a putative tryptophan/tyrosine transport system substrate-binding protein, in more detail. We compared growth capacities of the isogenic trpX-deficient mutant derivative strain 10∆trpX with its parent. Growth experiments in chemically defined media (CDM) revealed that growth of 10∆trpX depended on tryptophan concentration, suggesting TrpX involvement in tryptophan uptake. We demonstrated that trpX is part of an operon structure and co-transcribed with two additional genes encoding a putative permease and ATPase, respectively. Bioinformatics analysis identified a putative tryptophan T-box riboswitch in the 5′ untranslated region of this operon. Finally, qRT-PCR and a reporter activation assay revealed trpX mRNA induction under tryptophan-limited conditions. In conclusion, our study showed that TrpX is part of a putative tryptophan ABC transporter system regulated by a T-box riboswitch probably functioning as a substrate-binding protein. Due to the tryptophan auxotrophy of S. suis, TrpX plays a crucial role for metabolic adaptation and growth during infection.

Connections between Exoproteome Heterogeneity and Virulence in the Oral Pathogen Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a Gram-negative bacterial pathogen associated with severe periodontitis and nonoral diseases. Clinical isolates of A. actinomycetemcomitans display a rough (R) colony phenotype with strong adherent properties. Upon prolonged culturing, nonadherent strains with a smooth (S) colony phenotype emerge. To date, most virulence studies on A. actinomycetemcomitans have been performed with S strains of A. actinomycetemcomitans, whereas the virulence of clinical R isolates has received relatively little attention. Since the extracellular proteome is the main bacterial reservoir of virulence factors, the present study was aimed at a comparative analysis of this subproteome fraction for a collection of R isolates and derivative S strains, in order to link particular proteins to the virulence of A. actinomycetemcomitans with serotype b. To assess the bacterial virulence, we applied different infection models based on larvae of the greater wax moth Galleria mellonella, a human salivary gland-derived epithelial cell line, and freshly isolated neutrophils from healthy human volunteers. A total number of 351 extracellular A. actinomycetemcomitans proteins was identified by mass spectrometry, with the S strains consistently showing more extracellular proteins than their parental R isolates. A total of 50 known extracellular virulence factors was identified, of which 15 were expressed by all investigated bacteria. Importantly, the comparison of differences in exoproteome composition and virulence highlights critical roles of 10 extracellular proteins in the different infection models. Together, our findings provide novel clues for understanding the virulence of A. actinomycetemcomitans and for development of potential preventive or therapeutic avenues to neutralize this important oral pathogen.

IMPORTANCE Periodontitis is one of the most common inflammatory diseases worldwide, causing high morbidity and decreasing the quality of life of millions of people. The bacterial pathogen Aggregatibacter actinomycetemcomitans is strongly associated with aggressive forms of periodontitis. Moreover, it has been implicated in serious nonoral infections, including endocarditis and brain abscesses. Therefore, it is important to investigate how A. actinomycetemcomitans can cause disease. In the present study, we applied a mass spectrometry approach to make an inventory of the virulence factors secreted by different clinical A. actinomycetemcomitans isolates and derivative strains that emerged upon culturing. We subsequently correlated the secreted virulence factors to the pathogenicity of the investigated bacteria in different infection models. The results show that a limited number of extracellular virulence factors of A. actinomycetemcomitans have central roles in pathogenesis, indicating that they could be druggable targets to prevent or treat oral disease.

Proteomic Study of the Adaptive Mechanism of Ciprofloxacin-Resistant Staphylococcus aureus to the Host Environment

Antibiotic-resistant bacteria can escape host immune killing and settle in the host to form persistent infections. In this study we investigated the adaptive mechanism of resistant Staphylococcus aureus to the host environment by data-independent acquisition-based quantitative proteomics and functional validation. The growth curve and minimum inhibitory concentration (MIC) indicated that ciprofloxacin-resistant (Cip-R) S. aureus showed a survival advantage over sensitive strains. Cip-R also exhibited a stronger invasion and biofilm formation ability than sensitive bacteria. Cip-R stimulation resulted in the improved production of inflammatory factors of the host cells. Proteomics study combined with biochemical validations showed that Cip-R obtained adaptability to the host via upregulation of the tricarboxylic acid cycle (TCA cycle) and downregulation of ribosome metabolism and protein folding to maintain energy to support Cip-R's survival. Thus, this study will help us to further explain the growth strategy of resistant bacteria to adapt to the host environment, and provide important information for the development of new antibacterial drugs.

Influence of Polysaccharides From Polygonatum kingianum on Short-Chain Fatty Acid Production and Quorum Sensing in Lactobacillus faecis

Polysaccharide is one of the main active ingredients of Polygonatum kingianum, which has been proven to regulate the balance of gut microbiota. For the first time, this study focused on the regulation of polysaccharides from Polygonatum kingianum (PS) on Lactobacillus faecis, a specific probiotic in the intestinal tract. PS effectively promoted the biomass, biofilm and acetic acid production in L. faecis 2-84, and enhanced quorum sensing (QS) signaling. The characteristics of gene sequence were analyzed using genomics approaches, and L. faecis 2-84 was found to encode 18 genes that are closely related to QS and 10 genes related to short-chain fatty acids (SCFAs). Additionally, transcriptome and proteome analysis demonstrated that PS could promote the QS system of L. faecis by enhancing the transcription of oppA gene and expression of oppD protein. PS also regulated the production and metabolism of SCFAs of L. faecis by upregulating the expression of ldh and metE gene and adh2 protein, and downregulating the expression of mvK gene. In conclusion, it was speculated that PS could affect intestinal SCFAs production by affecting the QS system and SCFAs production in L. faecis. The present study implied that PS might have a role in promoting the growth of intestinal probiotics, where the QS system and SCFAs might be two of the important mechanisms for the probiotic activity of PS.

The type II histidine triad protein HtpsC facilitates invasion of epithelial cells by highly virulent Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is an important zoonotic pathogen that presents a significant threat both to pigs and to workers in the pork industry. The initial steps of S. suis 2 pathogenesis are unclear. In this study, we found that the type II histidine triad protein HtpsC from the highly virulent Chinese isolate 05ZYH33 is structurally similar to internalin A (InlA) from Listeria monocytogenes, which plays an important role in mediating listerial invasion of epithelial cells. To determine if HtpsC and InlA function similarly, an isogenic htpsC mutant (ΔhtpsC) was generated in S. suis by homologous recombination. The htpsC deletion strain exhibited a diminished ability to adhere to and invade epithelial cells from different sources. Double immunofluorescence microscopy also revealed reduced survival of the ΔhtpsC mutant after co-cultivation with epithelium. Adhesion to epithelium and invasion by the wild type strain was inhibited by a monoclonal antibody against E-cadherin. In contrast, the htpsC-deficient mutant was unaffected by the same treatment, suggesting that E-cadherin is the host-cell receptor that interacts with HtpsC and facilitates bacterial internalization. Based on these results, we propose that HtpsC is involved in the process by which S. suis 2 penetrates host epithelial cells, and that this protein is an important virulence factor associated with cell adhesion and invasion.

Novel Streptococcus uberis sequence types causing bovine subclinical mastitis in Hainan, China

AIM

To determine the molecular epidemiology, genotypes, and phenotypes of the major species of Streptococcus associated with bovine subclinical mastitis in Hainan, China.

METHODS AND RESULTS

In total, 150 subclinical mastitis milk samples were collected from two large dairy farms in Hainan. On the basis of biochemical tests and 16S rDNA sequencing, 39 samples were Streptococcus positive and the most frequently isolated species was Streptococcus uberis (n=29, 74.4%). According to multilocus sequence typing (MLST), and assays of biofilm formation, antimicrobial susceptibility, resistance and virulence genes, the S. uberis isolates were clustered into nine new sequence types (STs; ST986-ST994), but were not merged into a clonal group (except for ST991 (CC143)). All isolates produced biofilm, but most weakly. The dominant virulence pattern was hasABC + sua + gapC + oppF + pauA + mtuA + cfu (27/29, 91.1%), based on the 11 virulence genes tested. The majority of isolates (88.46%) carried at least one resistance gene and more than half (58.62%) were multidrug-resistant. The main resistance genes were linB (65.5%), ermB (37.9%), and tetS (34.5%), among the six antibiotic resistance genes and 11 antimicrobials tested.

CONCLUSION

Environmental S. uberis is important in bovine subclinical mastitis in Hainan.

SIGNIFICANCE AND IMPACT OF THE STUDY

S. uberis isolates in Hainan, China, show distinct MLST, virulence, and antibiotic resistance characteristics.

Anatomical Site, Typing, Virulence Gene Profiling, Antimicrobial Susceptibility and Resistance Genes of Streptococcus suis Isolates Recovered from Pigs in Spain

A set of 207 Streptococcus suis isolates were collected from ten autonomous communities from Spain in 2019 to 2020 from pigs with meningitis, pneumonic lungs, arthritic joints or other swollen viscera, to a lesser extent. Thirteen capsular types were detected being the most prevalent serotype 2 (21.7%), followed by serotypes 1 (21.3%), 9 (19.3%) and 3 (6.3%). Serotypes 2 and 9 were recovered mainly from the central nervous system (CNS), while serotype 1 was isolated mostly from swollen joints and serotype 3 from the lungs. Twenty-five isolates (12.1%) could not be typed. The most prevalent pathotype was epf + mrp + sly + luxS (49 isolates, 23.8%), and it was related mainly to serotypes 1 and 2. Serotypes 1–3 and 9 were significantly associated with anatomical sites of isolation and virulence factors, serotype 9 (CNS) and serotypes 3 and 9 (lungs) being associated with virulence profiles without the epf gene. S. suis isolates showed globally high antimicrobial resistances, but ampicillin followed by spectinomycin and tiamulin resulted in the highest activities, while the greatest resistances were detected for sulphadimethoxine, tetracyclines, neomycin, clindamycin and macrolides. A total of 87.4% isolates were positive to the tetO gene, 62.4% to the ermB gene and 25.2% to the fexA gene, while 14.6% were positive to all three genes simultaneously. A significative association between isolate resistances to tetracyclines and macrolides and the resistance genes tested was established, except for phenicol resistance and the fexA gene. A set of 14 multiresistance patterns were obtained according to the number of antimicrobials to which the isolates were resistant, the resistances to 12 or more agents being the most prevalent ones. A remarkable amount of multiresistance profiles could be seen among the S. suis serotype 9 isolates.

Quantitative proteomic analysis reveals that serine/threonine kinase is involved in Streptococcus suis virulence and adaption to stress conditions

The eukaryotic-type serine/threonine kinase of Streptococcus suis serotype 2 (SS2) performs critical roles in bacterial pathogenesis. In this study, isobaric tags for relative and absolute quantification (iTRAQ) MS/MS were used to analyze the protein profiles of wild type strain SS2-1 and its isogenic STK deletion mutant (Δstk). A total of 281 significant differential proteins, including 147 up-regulated and 134 down-regulated proteins, were found in Δstk. Moreover, 69 virulence factors (VFs) among these 281 proteins were predicted by the Virulence Factor Database (VFDB), including 38 downregulated and 31 up-regulated proteins in Δstk, among which 15 down regulated VFs were known VFs of SS2. Among the down-regulated proteins, high temperature requirement A (HtrA), glutamine synthase (GlnA), ferrichrome ABC transporter substrate-binding protein FepB, and Zinc-binding protein AdcA are known to be involved in bacterial survival and/or nutrient and energy acquisition under adverse host conditions. Overall, our results indicate that STK regulates the expression of proteins involved in virulence of SS2 and its adaption to stress environments.

Evaluation of immunogenicity and protection mediated by Lawsonia intracellularis subunit vaccines

Lawsonia intracellularis is an economically important bacterium that causes ileitis in pigs. Current vaccines for L. intracellularis do not allow for differentiation between infected and vaccinated animals (DIVA), which is beneficial for disease tracking and surveillance. Previously, we identified five putative surface L. intracellularis proteins that were targeted by antibodies from pigs infected with L. intracellularis which could serve as antigens in a subunit vaccine. We conducted two trials to determine whether these antigens were immunogenic and provided protection against infectious challenge and whether truncated glycoprotein D could be used as a DIVA antigen. For Trial 1, 5 week-old piglets were administered intramuscular monovalent vaccines comprised of a recombinant (r) flagella subunit protein (rFliC,) and DIVA antigen (truncated glycoprotein D (TgD), a herpes virus antigen) both formulated with a combination adjuvant consisting of polyinosinic:polycytidylic acid(poly I:C), host defense peptide 1002 and polyphosphazene, referred to as Triple Adjuvant (TriAdj). Relative to control animals, animals vaccinated with rFliC and rTgD had significantly elevated antigen-specific humoral immunity in sera suggesting that rFliC and TgD are immunogenic. Control animals had negligible anti-TgD titres suggesting that TgD may be a suitable DIVA antigen for pigs. For Trial 2, piglets were immunized with a trivalent vaccine (FOG vaccine consisting of rFLiC, rOppA protein (a ABC Type dipeptide transport system) and rGroEL (a stress response protein)) and a divalent vaccine (CM vaccine consisting of rClpP (an ATP-dependent Clp protease proteolytic subunit) and rMetK (a S-adenosyl methionine synthase)) formulated with Emulsigen®. Relative to the control pigs, pigs immunized with the FOG vaccine produced robust and significantly higher serum IgG antibodies against rFliC and rGroEL, and significantly higher anti-FliC and anti-GroEL IgA antibodies in jejunal (GroEL only) and ileal intestinal mucosa. Pigs immunized with CM vaccine produced significantly higher serum antibodies against rClpP and rMetK and significantly higher anti-rClpP IgA antibodies in the ileum relative to the control pigs. Quantitative polymerase chain reaction (qPCR) analysis showed that 18 days after challenge with infectious L. intracellularis, challenged/control pigs and pigs that received the CM vaccine, but not the pigs vaccinated with the FOG vaccine, shed significantly more bacteria in feces than the unchallenged controls pigs. These data suggest that the FOG vaccinated pigs showed limited protection. While promising, more work is needed to enhance the efficiency of the intramuscular vaccine to show significant disease protection.

Genetic analysis and pathogenicity of different sequence types of Streptococcus suis isolated from pigs in southern China

In this study, 52 Streptococcus suis isolates from pigs in southern China were divided into four known sequence types (STs) and six new STs, using multilocus sequence typing. Ten representative isolates were selected from 10 STs for the analysis of whole genome sequences. Virulence was assessed in 10 isolates, which were classified into three pathogenic groups. The prevalence of virulence-associated factors in the moderately pathogenic group was higher than that in the highly pathogenic group. The isolates from ST1 complex and serotype 2 were allocated to the moderately pathogenic group, while the isolates from the highly pathogenic group belonged to the non-ST1 complex and non-serotype 2. Three clusters were obtained based on multilocus sequence typing sequences: cluster III isolates from the nasal cavity of healthy pigs were classified into the highly pathogenic group and showed many peculiarities compared with cluster I and II isolates in virulence genotypes, genetic typing and pathogenesis, indicating a potential independent evolutionary line. Our results suggest that S. suis infections in China are becoming more complicated with constantly mutating isolates, which makes it difficult to distinguish their virulence by recognized typing methods. Thus, increased investigation and monitoring of these infections should be a priority for the swine industry in China.

Streptococcus suis pathogenesis-A diverse array of virulence factors for a zoonotic lifestyle

Streptococcus suis is a major cause of respiratory tract and invasive infections in pigs and is responsible for a substantial disease burden in the pig industry. S. suis is also a significant cause of bacterial meningitis in humans, particularly in South East Asia. S. suis expresses a wide array of virulence factors, and although many are described as being required for disease, no single factor has been demonstrated to be absolutely required. The lack of uniform distribution of known virulence factors among individual strains and lack of evidence that any particular virulence factor is essential for disease makes the development of vaccines and treatments challenging. Here we review the current understanding of S. suis virulence factors and their role in the pathogenesis of this important zoonotic pathogen.

HP1717 Contributes to Streptococcus suis Virulence by Inducing an Excessive Inflammatory Response and Influencing the Biosynthesis of the Capsule

Streptococcus suis 2 (SS2) is an important zoonotic pathogen that substantially harms the swine industry and poses threats to human health. Excessive inflammation is considered to be a hallmark of SS2 infection because it is responsible for most clinical signs of SS2, especially streptococcal toxic shock-like syndrome. However, the current knowledge of SS2-induced excessive inflammation remains limited. In this study, we identified HP1717 as a novel extracellular pro-inflammatory protein in SS2 that can induce robust expression of inflammatory cytokines in RAW264.7 macrophages. Notably, the pro-inflammatory ability of HP1717 was dose-dependent and heat-sensitive, and it required the recognition of Toll-like receptor 2 (TLR2) and the phosphorylation of both extracellular signal-regulated kinases 1/2 (ERK1/2) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Further, by constructing a deletion mutant, we demonstrated that HP1717 significantly influenced the biosynthesis of the bacterial capsule, which plays a critical role in the virulence of SS2 by interfering with the ability of host immune cells to phagocytize and kill the pathogen. Indeed, the mutant strain displayed reduced resistance to whole-blood killing compared with the wild strain. Finally, murine experiments indicated that the deletion of hp1717 in SS2 reduced the lethality, pro-inflammatory activity, and bacterial loads in mice. Collectively, our data reveal HP1717 as a novel virulence-related factor of SS2 that can induce an excessive inflammatory response and significantly affect the bacterial capsule, thus expanding our understanding of the pathogenesis of S. suis.

Molecular Basis of Unexpected Specificity of ABC Transporter-Associated Substrate-Binding Protein DppA from Helicobacter pylori

The gastric pathogen Helicobacter pylori has limited ability to use carbohydrates as a carbon source, relying instead on exogenous amino acids and peptides. Uptake of certain peptides by H. pylori requires an ATP binding cassette (ABC) transporter annotated dipeptide permease (Dpp). The transporter specificity is determined by its cognate substrate-binding protein DppA, which captures ligands in the periplasm and delivers them to the permease. Here, we show that, unlike previously characterized DppA proteins, H. pylori DppA binds, with micromolar affinity, peptides of diverse amino acid sequences ranging between two and eight residues in length. We present analysis of the 1.45-Å-resolution crystal structure of its complex with the tetrapeptide STSA, which provides a structural rationale for the observed broad specificity. Analysis of the molecular surface revealed a ligand-binding pocket that is large enough to accommodate peptides of up to nine residues in length. The structure suggests that H. pylori DppA is able to recognize a wide range of peptide sequences by forming interactions primarily with the peptide main chain atoms. The loop that terminates the peptide-binding pocket in DppAs from other bacteria is significantly shorter in the H. pylori protein, providing an explanation for its ability to bind longer peptides. The subsites accommodating the two N-terminal residues of the peptide ligand make the greatest contribution to the protein-ligand binding energy, in agreement with the observation that dipeptides bind with affinity close to that of longer peptides.IMPORTANCE The World Health Organization listed Helicobacter pylori as a high-priority pathogen for antibiotic development. The potential of using peptide transporters in drug design is well recognized. We discovered that the substrate-binding protein of the ABC transporter for peptides, termed dipeptide permease, is an unusual member of its family in that it directly binds peptides of diverse amino acid sequences, ranging between two and eight residues in length. We also provided a structural rationale for the observed broad specificity. Since the ability to import peptides as a source of carbon is critical for H. pylori, our findings will inform drug design strategies based on inhibition or fusion of membrane-impermeant antimicrobials with peptides.

Immunoproteomic analysis of Lawsonia intracellularis identifies candidate neutralizing antibody targets for use in subunit vaccine development

Lawsonia intracellularis is an obligate intracellular microorganism and the causative agent of porcine proliferative enteropathy. Due to its obligate intracellular nature, characterization of antigens and proteins involved in host-pathogen interaction and immune recognition have been difficult to achieve using conventional microbiological techniques. In this work, we used 2-dimensional gel electrophoresis coupled with Western-immunoblotting, mass spectrometry and bioinformatics to identify bacterial proteins that interact in vitro with pig intestinal cells (IPEC-1), have immunogenic properties and the potential to be used as subunit vaccine antigens. We detected eleven immunogenic bacterial proteins from which fliC (LI0710), LI1153 (annotated by NCBI as Putative protein N), and LI0649 (annotated as autotransporter) were predicted to be expressed on the outer membrane while LI0169 (oppA; annotated as ABC dipeptide transport system) was predicted to be periplasmic with a transmembrane domain forming a central pore through the plasma membrane. Genes coding for these four proteins were cloned and expressed in Escherichia coli and the corresponding recombinant proteins were purified using affinity chromatography. Porcine hyperimmune serum against whole Lawsonia lysate established that all four recombinant proteins were immunogenic. Further, rabbit hyperimmune sera generated against the vaccine strain of L. intracellularis and rabbit serum specific for each recombinant protein showed an inhibitory effect on the attachment and penetration of live, avirulent L. intracellularis, thus indicating that each protein is a potential neutralizing antibody target and a candidate for subunit vaccine formulation.

Effect of fermented milk from Lactococcus lactis ssp. cremoris strain JFR1 on Salmonella invasion of intestinal epithelial cells

The process of fermentation contributes to the organoleptic properties, preservation, and nutritional benefits of food. Fermented food may interfere with pathogen infections through a variety of mechanisms, including competitive exclusion or improving intestinal barrier integrity. In this study, the effect of milk fermented with Lactococcus lactis ssp. cremoris JFR1 on Salmonella invasion of intestinal epithelial cell cultures was investigated. Epithelial cells (HT29-MTX, Caco-2, and cocultures of the 2) were treated for 1 h with Lactococcus lactis ssp. cremoris JFR1 fermented milk before infection with Salmonella enterica ssp. enterica Typhimurium. Treatment with fermented milk resulted in increased transepithelial electrical resistance, which remained constant for the duration of infection (up to 3 h), illustrating a protective effect. After gentamicin treatment to remove adhered bacterial cells, enumeration revealed a reduction in numbers of intracellular Salmonella. Quantitative reverse-transcription PCR data indicated a downregulation of Salmonella virulence genes hilA, invA, and sopD after treatment with fermented milk. Fermented milk treatment of epithelial cells also exhibited an immunomodulatory effect reducing the production of proinflammatory IL-8. In contrast, chemically acidified milk (glucono delta-lactone) failed to show the same effect on monolayer integrity, Salmonella Typhimurium invasion, and gene expression as well as immune modulation. Furthermore, an oppA knockout mutant of Salmonella Typhimurium infecting treated epithelial cells did not show suppressed virulence gene expression. Collectively, these results suggest that milk fermented with Lactococcus lactis ssp. cremoris JFR1 is effective in vitro in the reduction of Salmonella invasion into intestinal epithelial cells. A functional OppA permease in Salmonella is required to obtain the antivirulence effect of fermented milk.

Examination of Australian Streptococcus suis isolates from clinically affected pigs in a global context and the genomic characterisation of ST1 as a predictor of virulence

Streptococcus suis is a major zoonotic pathogen that causes severe disease in both humans and pigs. Australia's pig herd has been quarantined for over 30 years, however S. suis remains a significant cause of disease. In this study, we investigated S. suis from 148 cases of clinical disease in pigs from 46 pig herds over a period of seven years, to determine the level of genetic difference from international isolates that may have arisen over the 30 years of separation. Isolates underwent whole genome sequencing, genome analysis and antimicrobial susceptibility testing. Data was compared at the core genome level to clinical isolates from overseas. Results demonstrated five predominant multi-locus sequence types and two major cps gene types (cps2 and 3). At the core genome level Australian isolates clustered predominantly within one large clade consisting of isolates from the UK, Canada and North America. A small proportion of Australian swine isolates (5%) were phylogenetically associated with south-east Asian and UK isolates, many of which were classified as causing systemic disease, and derived from cases of human and swine disease. Based on this dataset we provide a comprehensive outline of the current S. suis clones associated with disease in Australian pigs and their global context, with the main finding being that, despite three decades of separation, Australian S. suis are genomically similar to overseas strains. In addition, we show that ST1 clones carry a constellation of putative virulence genes not present in other Australian STs.