Relevance of the two-component sensor protein CiaH to acid and oxidative stress responses in Streptococcus pyogenes

Lactiplantibacillus plantarum KAU007 Extract Modulates Critical Virulence Attributes and Biofilm Formation in Sinusitis Causing Streptococcus pyogenes

Streptococcus pyogenes is one of the most common bacteria causing sinusitis in children and adult patients. Probiotics are known to cause antagonistic effects on S. pyogenes growth and biofilm formation. In the present study, we demonstrated the anti-biofilm and anti-virulence properties of Lactiplantibacillus plantarum KAU007 against S. pyogenes ATCC 8668. The antibacterial potential of L. plantarum KAU007 metabolite extract (LME) purified from the cell-free supernatant of L. plantarum KAU007 was evaluated in terms of minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC). LME was further analyzed for its anti-biofilm potential using crystal violet assay and microscopic examination. Furthermore, the effect of LME was tested on the important virulence attributes of S. pyogenes, such as secreted protease production, hemolysis, extracellular polymeric substance production, and cell surface hydrophobicity. Additionally, the impact of LME on the expression of genes associated with biofilm formation and virulence attributes was analyzed using qPCR. The results revealed that LME significantly inhibited the growth and survival of S. pyogenes at a low concentration (MIC, 9.76 µg/mL; MBC, 39.06 µg/mL). Furthermore, LME inhibited biofilm formation and mitigated the production of extracellular polymeric substance at a concentration of 4.88 μg/mL in S. pyogenes. The results obtained from qPCR and biochemical assays advocated that LME suppresses the expression of various critical virulence-associated genes, which correspondingly affect various pathogenicity markers and were responsible for the impairment of virulence and biofilm formation in S. pyogenes. The non-hemolytic nature of LME and its anti-biofilm and anti-virulence properties against S. pyogenes invoke further investigation to study the role of LME as an antibacterial agent to combat streptococcal infections.

Carvacrol inhibits Streptococcus pyogenes biofilms by suppressing the expression of genes associated with quorum-sensing and reducing cell surface hydrophobicity

Streptococcus pyogenes is a leading cause of chronic and acute infections, including streptococcus pharyngitis. Biofilm formation by S. pyogenes can cause tolerance against antibiotics. Although penicillin remains the first choice of antibiotic for S. pyogenes, alternative approaches have gained interest due to treatment failures and hypersensitive individuals. Carvacrol is a monoterpenoid from herbal plants with selective biocidal activity on S. pyogenes. Therefore, the present study reveals the efficacy of carvacrol in inhibiting and eradicating S. pyogenes biofilm. The antibiofilm activities were investigated using colorimetric assays, microscopy, cell surface hydrophobicity, gene expression analysis, and in-silico analysis. Carvacrol also showed a minimum biofilm inhibitory concentration (MBIC) against S. pyogenes of 125 μg/mL. The electron microscopic and confocal microscopic analyses revealed a dose-dependent suppression of biofilm formation and a reduction in the biofilm thickness by carvacrol. Carvacrol also inhibited the biofilm-associated virulence factors such as cell surface hydrophobicity. Quantitative real-time polymerase chain reaction analysis showed the downregulation of speB, srtB, luxS, covS, dltA, ciaH, and hasA genes involved in biofilm formation. The results suggested the therapeutic potential of carvacrol against biofilm-associated streptococcal infections.

Comparative Metabolic Pathways Analysis and Subtractive Genomics Profiling to Prioritize Potential Drug Targets Against Streptococcus pneumoniae

Streptococcus pneumoniae is a notorious pathogen that affects ∼450 million people worldwide and causes up to four million deaths per annum. Despite availability of antibiotics (i.e., penicillin, doxycycline, or clarithromycin) and conjugate vaccines (e.g., PCVs), it is still challenging to treat because of its drug resistance ability. The rise of antibiotic resistance in S. pneumoniae is a major source of concern across the world. Computational subtractive genomics is one of the most applied techniques in which the whole proteome of the bacterial pathogen is gradually reduced to a limited number of potential therapeutic targets. Whole-genome sequencing has greatly reduced the time required and provides more opportunities for drug target identification. The goal of this work is to evaluate and analyze metabolic pathways in serotype 14 of S. pneumonia to identify potential drug targets. In the present study, 47 potent drug targets were identified against S. pneumonia by employing the computational subtractive genomics approach. Among these, two proteins are prioritized (i.e., 4-oxalocrotonate tautomerase and Sensor histidine kinase uniquely present in S. pneumonia) as novel drug targets and selected for further structure-based studies. The identified proteins may provide a platform for the discovery of a lead drug candidate that may be capable of inhibiting these proteins and, therefore, could be helpful in minimizing the associated risk related to the drug-resistant S. pneumoniae. Finally, these enzymatic proteins could be of prime interest against S. pneumoniae to design rational targeted therapy.

Streptococcus pyogenes ("Group A Streptococcus"), a Highly Adapted Human Pathogen-Potential Implications of Its Virulence Regulation for Epidemiology and Disease Management

Streptococcus pyogenes (group A streptococci; GAS) is an exclusively human pathogen. It causes a variety of suppurative and non-suppurative diseases in people of all ages worldwide. Not all can be successfully treated with antibiotics. A licensed vaccine, in spite of its global importance, is not yet available. GAS express an arsenal of virulence factors responsible for pathological immune reactions. The transcription of all these virulence factors is under the control of three types of virulence-related regulators: (i) two-component systems (TCS), (ii) stand-alone regulators, and (iii) non-coding RNAs. This review summarizes major TCS and stand-alone transcriptional regulatory systems, which are directly associated with virulence control. It is suggested that this treasure of knowledge on the genetics of virulence regulation should be better harnessed for new therapies and prevention methods for GAS infections, thereby changing its global epidemiology for the better.

Arginine Decarboxylase Is Essential for Pneumococcal Stress Responses

Polyamines such as putrescine, cadaverine, and spermidine are small cationic molecules that play significant roles in cellular processes, including bacterial stress responses and host–pathogen interactions. Streptococcus pneumoniae is an opportunistic human pathogen, which causes several diseases that account for significant morbidity and mortality worldwide. As it transits through different host niches, S. pneumoniae is exposed to and must adapt to different types of stress in the host microenvironment. We earlier reported that S. pneumoniae TIGR4, which harbors an isogenic deletion of an arginine decarboxylase (ΔspeA), an enzyme that catalyzes the synthesis of agmatine in the polyamine synthesis pathway, has a reduced capsule. Here, we report the impact of arginine decarboxylase deletion on pneumococcal stress responses. Our results show that ΔspeA is more susceptible to oxidative, nitrosative, and acid stress compared to the wild-type strain. Gene expression analysis by qRT-PCR indicates that thiol peroxidase, a scavenger of reactive oxygen species and aguA from the arginine deiminase system, could be important for peroxide stress responses in a polyamine-dependent manner. Our results also show that speA is essential for endogenous hydrogen peroxide and glutathione production in S. pneumoniae. Taken together, our findings demonstrate the critical role of arginine decarboxylase in pneumococcal stress responses that could impact adaptation and survival in the host.

Usnic acid deteriorates acidogenicity, acidurance and glucose metabolism of Streptococcus mutans through downregulation of two-component signal transduction systems

The principal etiological agent of human dental caries, Streptococcus mutans is a multi-virulent pathogen that can transform commensal oral microbial community to plaque biofilms. Major virulence factors that are associated with the cariogenicity of S. mutans include adhesion, acidogenicity and acidurity. All these pathogenic traits coordinate and alter the dental plaque ecology which provide room for interaction with other similar acidogenic and aciduric bacteria. This cariogenic flora increases the possibility of enamel demineralization which headway to caries development. The present study was aimed at evaluating the antimicrobial and antiinfective potential of a lichen secondary metabolite usnic acid (UA) against S. mutans. Minimum inhibitory concentration (MIC), Minimum bactericidal concentration (MBC) and growth kinetics were evaluated to determine the antimicrobial potential of UA against S. mutans. UA at 5 µg mL-1 and 10 µg mL-1 concentration were considered as MIC and MBC respectively. Effect on biofilm formation was microscopically assessed and found to be reduced in a concentration dependent manner. Gene expression of gtfB, gtfC, gtfD, vicR, ComDE and smu0630 was found to be downregulated upon treatment with sub-MIC of UA. Acidogenicity, acidurity, eDNA synthesis and response to oxidative stress were found to be attenuated by the influence of UA. It was also demonstrated to act on preformed mature biofilm of S. mutans. Moreover, UA was shown to possess very low frequency to acquire spontaneous resistance development in S. mutans. Besides, no morphological aberrations or toxic effect was instigated by UA in the human buccal epithelial cells as well as to the oral commensals. Altogether, these results demonstrate the therapeutic potential of usnic acid in the treatment of S. mutans infection.

Single Amino Acid Replacements in RocA Disrupt Protein-Protein Interactions To Alter the Molecular Pathogenesis of Group A Streptococcus

Group A Streptococcus (GAS) is a human-specific pathogen and major cause of disease worldwide. The molecular pathogenesis of GAS, like many pathogens, is dependent on the coordinated expression of genes encoding different virulence factors. The control of virulence regulator/sensor (CovRS) two-component system is a major virulence regulator of GAS that has been extensively studied. More recent investigations have also involved regulator of Cov (RocA), a regulatory accessory protein to CovRS. RocA interacts, in some manner, with CovRS; however, the precise molecular mechanism is unknown. Here, we demonstrate that RocA is a membrane protein containing seven transmembrane helices with an extracytoplasmically located N terminus and cytoplasmically located C terminus. For the first time, we demonstrate that RocA directly interacts with itself (RocA) and CovS, but not CovR, in intact cells. Single amino acid replacements along the entire length of RocA disrupt RocA-RocA and RocA-CovS interactions to significantly alter the GAS virulence phenotype as defined by secreted virulence factor activity in vitro and tissue destruction and mortality in vivo In summary, we show that single amino acid replacements in a regulatory accessory protein can affect protein-protein interactions to significantly alter the virulence of a major human pathogen.

5-Hydroxymethylfurfural inhibits Acinetobacter baumannii biofilms: an in vitro study

The present study was aimed to investigate the antibiofilm activity of 5-hydroxymethylfurfural against Acinetobacter baumanni and Vellar estuary isolates v3 (Acinetobacter nosocomialis). The biofilm inhibitory concentration (BIC) of 5HMF against A. baumannii and v3 (A. nosocomialis) was found to be 100 µg/ml) exhibited non-bactericidal concentration-dependent antibiofilm activities against Acinetobacter species. The present study found that 5HMF treatment is very effective in the initial stage of A. baumannii biofilms and it significantly disrupted the mature biofilms. Moreover, 5HMF treatment inhibited the extracellular polymeric substances (EPS), including polysaccharides and proteins production. Results from gene expression and in vitro assays further demonstrated the 5HMF treatment downregulated the expression of bfmR, bap, csuA/B, ompA and katE virulence genes, which consistently affects biofilm formation and its mediated virulence property. The present study suggests that 5HMF unveil its antibiofilm activity by interfering initial biofilm formation and suppressing the virulence regulator genes in A. baumannii. Further studies are required to explore the 5HMF mode of action responsible for the antibiofilm activity.

Eucalyptol inhibits biofilm formation of Streptococcus pyogenes and its mediated virulence factors

Introduction. Streptococcus pyogenes is a diverse virulent synthesis pathogen responsible for invasive systemic infections. Establishment of antibiotic resistance in the pathogen has produced a need for new antibiofilm agents to control the biofilm formation and reduce biofilm-associated resistance development.Aim. The present study investigates the in vitro antibiofilm activity of eucalyptol against S. pyogenes.Methodology. The antibiofilm potential of eucalyptol was assessed using a microdilution method and their biofilm inhibition efficacy was visualized by microscopic analysis. The biochemical assays were performed to assess the influence of eucalyptol on virulence productions. Real-time PCR analysis was performed to evaluate the expression profile of the virulence genes.Results. Eucalyptol showed significant antibiofilm potential in a dose-dependent manner without affecting bacterial growth. Eucalyptol at 300 µg ml^-1 (biofilm inhibitory concentration) significantly inhibited the initial stage of biofilm formation in S. pyogenes. However, eucalyptol failed to diminish the mature biofilms of S. pyogenes at biofilm inhibitory concentration and it effectively reduced the biofilm formation on stainless steel, titanium, and silicone surfaces. The biochemical assay results revealed that eucalyptol greatly affects the cell-surface hydrophobicity, auto-aggregation, extracellular protease, haemolysis and hyaluronic acid synthesis. Further, the gene-expression analysis results showed significant downregulation of virulence gene expression upon eucalyptol treatment.Conclusion. The present study suggests that eucalyptol applies its antibiofilm assets by intruding the initial biofilm formation of S. pyogenes. Supplementary studies are needed to understand the mode of action involved in biofilm inhibition.

Quebrachitol inhibits biofilm formation and virulence production against methicillin-resistant Staphylococcus aureus

The present study evaluated the quebrachitol (QBC) antibiofilm and antivirulence potential against methicillin-resistant Staphylococcus aureus (MRSA). QBC inhibited MRSA biofilm formation at concentration dependent manner without affecting the bacterial growth. Then, QBC biofilm efficacy was confirmed with light and confocal laser scanning microscopy analysis. QBC treatment significantly inhibited the biofilm formation on stainless steel, titanium and silicone surfaces. Besides, QBC treatment significantly reduced the MRSA virulence productions such as lipase and hemolysis. Moreover, it reduced MRSA survival rate in the presence of hydrogen peroxide. QBC treatment inhibited the MRSA adherence on hydrophobic, hydrophilic, collagen coating and fibrinogen coating surfaces. As well as it significantly reduced the autolysin and bacterial aggregation progress. The real-time PCR analysis revealed the ability of QBC downregulated the virulence genes expression including global regulator sarA, agr and polysaccharide intracellular adhesion (PIA) encode ica. The cumulative results of the present study suggest that QBC as a potential agent to combat against MRSA pathogenesis.

New Pathogenesis Mechanisms and Translational Leads Identified by Multidimensional Analysis of Necrotizing Myositis in Primates

A fundamental goal of contemporary biomedical research is to understand the molecular basis of disease pathogenesis and exploit this information to develop targeted and more-effective therapies. Necrotizing myositis caused by the bacterial pathogen Streptococcus pyogenes is a devastating human infection with a high mortality rate and few successful therapeutic options. We used dual transcriptome sequencing (RNA-seq) to analyze the transcriptomes of S. pyogenes and host skeletal muscle recovered contemporaneously from infected nonhuman primates. The in vivo bacterial transcriptome was strikingly remodeled compared to organisms grown in vitro, with significant upregulation of genes contributing to virulence and altered regulation of metabolic genes. The transcriptome of muscle tissue from infected nonhuman primates (NHPs) differed significantly from that of mock-infected animals, due in part to substantial changes in genes contributing to inflammation and host defense processes. We discovered significant positive correlations between group A streptococcus (GAS) virulence factor transcripts and genes involved in the host immune response and inflammation. We also discovered significant correlations between the magnitude of bacterial virulence gene expression in vivo and pathogen fitness, as assessed by previously conducted genome-wide transposon-directed insertion site sequencing (TraDIS). By integrating the bacterial RNA-seq data with the fitness data generated by TraDIS, we discovered five new pathogen genes, namely, S. pyogenes 0281 (Spy0281 [dahA]), ihk-irr, slr, isp, and ciaH, that contribute to necrotizing myositis and confirmed these findings using isogenic deletion-mutant strains. Taken together, our study results provide rich new information about the molecular events occurring in severe invasive infection of primate skeletal muscle that has extensive translational research implications.IMPORTANCE Necrotizing myositis caused by Streptococcus pyogenes has high morbidity and mortality rates and relatively few successful therapeutic options. In addition, there is no licensed human S. pyogenes vaccine. To gain enhanced understanding of the molecular basis of this infection, we employed a multidimensional analysis strategy that included dual RNA-seq and other data derived from experimental infection of nonhuman primates. The data were used to target five streptococcal genes for pathogenesis research, resulting in the unambiguous demonstration that these genes contribute to pathogen-host molecular interactions in necrotizing infections. We exploited fitness data derived from a recently conducted genome-wide transposon mutagenesis study to discover significant correlation between the magnitude of bacterial virulence gene expression in vivo and pathogen fitness. Collectively, our findings have significant implications for translational research, potentially including vaccine efforts.

Impact of Citral and Phloretin, Alone and in Combination, on Major Virulence Traits of Streptococcus pyogenes

Streptococcus pyogenes is well documented as a multi-virulent and exclusively human pathogen. The LuxS-based signaling in these bacteria has a crucial role in causing several infections through pathways that are pathogenic. This study evaluated the individual and synergistic effects of citral and phloretin against S. pyogenes in relation to major virulence traits. The in vitro synergy of citral and phloretin was evaluated by the checkerboard method. The fractional inhibitory concentration (FIC) values were calculated to determine the interactions between the inhibitors. The bacteria’s virulence properties were tested in the presence of the molecules, individually as well as in combination. Molecules’ cytotoxicity was tested using human tonsil epithelial cells. The synergistic effects of the molecules on the expression of biofilm and quorum sensing genes were tested using quantitative real-time polymerase chain reaction (qRT-PCR). The molecules were also tested for their impact on LuxS protein by molecular docking, modeling, and free-energy calculations. When the two molecules were assessed in combination (synergistic effect, FIC Index of 0.5), a stronger growth inhibitory activity was exhibited than the individual molecules. The cell surface hydrophobicity, as well as genes involved in quorum sensing and biofilm formation, showed greater suppression when the molecules were tested in combination. The in silico findings also suggest the inhibitory potential of the two molecules against LuxS protein. The binding orientation and the binding affinity of citral and phloretin well support the notion that there is a synergistic effect of citral and phloretin. The data reveal the combination of citral and phloretin as a potent antibacterial agent to combat the virulence of S. pyogenes.

Myrtenol Attenuates MRSA Biofilm and Virulence by Suppressing sarA Expression Dynamism

Methicillin-resistant Staphylococcus aureus (MRSA) is a deleterious human pathogen responsible for severe morbidity and mortality worldwide. The pathogen has attained high priority in the World Health Organization (WHO) - Multidrug-resistant (MDR) pathogens list. Emerging MDR strains of S. aureus are clinically challenging due to failure in conventional antibiotic therapy. Biofilm formation is one of the underlying mechanisms behind the antibiotic resistance. Hence, attenuating biofilm formation has become an alternative strategy to control persistent infections. The current study is probably the first that focuses on the antibiofilm and antivirulence potential of myrtenol against MRSA and its clinical isolates. Myrtenol exhibited a concentration-dependent biofilm inhibition without causing any harmful effect on cell growth and viability. Further, microscopic analysis validated the biofilm inhibitory efficacy of myrtenol against MRSA. In addition, myrtenol inhibited the synthesis of major virulence factors including slime, lipase, α-hemolysin, staphyloxanthin and autolysin. Inhibition of staphyloxanthin in turn sensitized the MRSA cells to healthy human blood and hydrogen peroxide (H2O2). Notably, myrtenol treated cells were deficient in extracellular DNA (eDNA) mediated autoaggregation as eDNA releasing autolysis was impaired by myrtenol. Biofilm disruptive activity on preformed biofilms was observed at concentrations higher than minimum biofilm inhibitory concentration (MBIC) of myrtenol. Also, the non-cytotoxic effect of myrtenol on human peripheral blood mononuclear cell (PBMC) was evidenced by trypan blue and Alamar blue assays. Transcriptional analysis unveiled the down-regulation of global regulator sarA and sarA mediated virulence genes upon myrtenol treatment, which is well correlated with results of phenotypic assays. Thus, the results of the present study revealed the sarA mediated antibiofilm and antivirulence potential of myrtenol against MRSA.

Polymorphisms in Regulator of Cov Contribute to the Molecular Pathogenesis of Serotype M28 Group A Streptococcus

Two-component systems (TCSs) are signal transduction proteins that enable bacteria to respond to external stimuli by altering the global transcriptome. Accessory proteins interact with TCSs to fine-tune their activity. In group A Streptococcus (GAS), regulator of Cov (RocA) is an accessory protein that functions with the control of virulence regulator/sensor TCS, which regulates approximately 15% of the GAS transcriptome. Whole-genome sequencing analysis of serotype M28 GAS strains collected from invasive infections in humans identified a higher number of missense (amino acid-altering) and nonsense (protein-truncating) polymorphisms in rocA than expected. We hypothesized that polymorphisms in RocA alter the global transcriptome and virulence of serotype M28 GAS. We used naturally occurring clinical isolates with rocA polymorphisms (n = 48), an isogenic rocA deletion mutant strain, and five isogenic rocA polymorphism mutant strains to perform genome-wide transcript analysis (RNA sequencing), in vitro virulence factor assays, and mouse and nonhuman primate pathogenesis studies to test this hypothesis. Results demonstrated that polymorphisms in rocA result in either a subtle transcriptome change, causing a wild-type-like virulence phenotype, or a substantial transcriptome change, leading to a significantly increased virulence phenotype. Each polymorphism had a unique effect on the global GAS transcriptome. Taken together, our data show that naturally occurring polymorphisms in one gene encoding an accessory protein can significantly alter the global transcriptome and virulence phenotype of GAS, an important human pathogen.

RocA Has Serotype-Specific Gene Regulatory and Pathogenesis Activities in Serotype M28 Group A Streptococcus

Serotype M28 group A streptococcus (GAS) is a common cause of infections such as pharyngitis ("strep throat") and necrotizing fasciitis ("flesh-eating" disease). Relatively little is known about the molecular mechanisms underpinning M28 GAS pathogenesis. Whole-genome sequencing studies of M28 GAS strains recovered from patients with invasive infections found an unexpectedly high number of missense (amino acid-changing) and nonsense (protein-truncating) polymorphisms in rocA (regulator of Cov), leading us to hypothesize that altered RocA activity contributes to M28 GAS molecular pathogenesis. To test this hypothesis, an isogenic rocA deletion mutant strain was created. Transcriptome sequencing (RNA-seq) analysis revealed that RocA inactivation significantly alters the level of transcripts for 427 and 323 genes at mid-exponential and early stationary growth phases, respectively, including genes for 41 transcription regulators and 21 virulence factors. In contrast, RocA transcriptomes from other GAS M protein serotypes are much smaller and include fewer transcription regulators. The rocA mutant strain had significantly increased secreted activity of multiple virulence factors and grew to significantly higher colony counts under acid stress in vitro RocA inactivation also significantly increased GAS virulence in a mouse model of necrotizing myositis. Our results demonstrate that RocA is an important regulator of transcription regulators and virulence factors in M28 GAS and raise the possibility that naturally occurring polymorphisms in rocA in some fashion contribute to human invasive infections caused by M28 GAS strains.

In silico characterisation of the two-component system regulators of Streptococcus pyogenes

Bacteria respond to environmental changes through the co-ordinated regulation of gene expression, often mediated by two-component regulatory systems (TCS). Group A Streptococcus (GAS), a bacterium which infects multiple human body sites and causes multiple diseases, possesses up to 14 TCS. In this study we examined genetic variation in the coding sequences and non-coding DNA upstream of these TCS as a method for evaluating relationships between different GAS emm-types, and potential associations with GAS disease. Twelve of the 14 TCS were present in 90% of the genomes examined. The length of the intergenic regions (IGRs) upstream of TCS coding regions varied from 39 to 345 nucleotides, with an average nucleotide diversity of 0.0064. Overall, IGR allelic variation was generally conserved with an emm-type. Subsequent phylogenetic analysis of concatenated sequences based on all TCS IGR sequences grouped genomes of the same emm-type together. However grouping with emm-pattern and emm-cluster-types was much weaker, suggesting epidemiological and functional properties associated with the latter are not due to evolutionary relatedness of emm-types. All emm5, emm6 and most of the emm18 genomes, all historically considered rheumatogenic emm-types clustered together, suggesting a shared evolutionary history. However emm1, emm3 and several emm18 genomes did not cluster within this group. These latter emm18 isolates were epidemiologically distinct from other emm18 genomes in study, providing evidence for local variation. emm-types associated with invasive disease or nephritogenicity also did not cluster together. Considering the TCS coding sequences (cds), correlation with emm-type was weaker than for the IGRs, and no strong correlation with disease was observed. Deletion of the malate transporter, maeP, was identified that serves as a putative marker for the emm89.0 subtype, which has been implicated in invasive outbreaks. A recombination-related, subclade-forming DNA motif was identified in the putative receiver domain of the Spy1556 response regulator that correlated with throat-associated emm-pattern-type A-C strains.

YvqE and CovRS of Group A Streptococcus Play a Pivotal Role in Viability and Phenotypic Adaptations to Multiple Environmental Stresses

Streptococcus pyogenes (group A Streptococcus, or GAS) is a human pathogen that causes a wide range of diseases. For successful colonization within a variety of host niches, GAS utilizes TCSs to sense and respond to environmental changes and adapts its pathogenic traits accordingly; however, many GAS TCSs and their interactions remain uncharacterized. Here, we elucidated the roles of a poorly characterized TCS, YvqEC, and a well-studied TCS, CovRS, in 2 different GAS strain SSI-1 and JRS4, respectively. Deletion of yvqE and yvqC in JRS4 resulted in lower cell viability and abnormality of cell division when compared to the wild-type strain under standard culture conditions, demonstrating an important role for YvqEC. Furthermore, a double-deletion of yvqEC and covRS in SSI-1 and JRS4 resulted in a significantly impaired ability to survive under various stress conditions, as well as an increased sensitivity to cell wall-targeting antibiotics compared to that observed in either single mutant or wild-type strains suggesting synergistic interactions. Our findings provide new insights into the impact of poorly characterized TCS (YvqEC) and potential synergistic interactions between YvqEC and CovRS and reveal their potential role as novel therapeutic targets against GAS infection.

Stress responses in Streptococcus species and their effects on the host

Streptococci cause a variety of diseases, such as dental caries, pharyngitis, meningitis, pneumonia, bacteremia, endocarditis, erysipelas, and necrotizing fasciitis. The natural niche of this genus of bacteria ranges from the mouth and nasopharynx to the skin, indicating that the bacteria will inevitably be subjected to environmental changes during invasion into the host, where it is exposed to the host immune system. Thus, the Streptococcus-host interaction determines whether bacteria are cleared by the host's defenses or whether they survive after invasion to cause serious diseases. If this interaction was to be deciphered, it could aid in the development of novel preventive and therapeutic agents. Streptococcus species possess many virulent factors, such as peroxidases and heat-shock proteins (HSPs), which play key roles in protecting the bacteria from hostile host environments. This review will discuss insights into the mechanism(s) by which streptococci adapt to host environments. Additionally, we will address how streptococcal infections trigger host stress responses; however, the mechanism by which bacterial components modulate host stress responses remains largely unknown.

covR Mediated Antibiofilm Activity of 3-Furancarboxaldehyde Increases the Virulence of Group A Streptococcus

BACKGROUND

Group A streptococcus (GAS, Streptococcus pyogenes), a multi-virulent, exclusive human pathogen responsible for various invasive and non-invasive diseases possesses biofilm forming phenomenon as one of its pathogenic armaments. Recently, antibiofilm agents have gained prime importance, since inhibiting the biofilm formation is expected to reduce development of antibiotic resistance and increase their susceptibility to the host immune cells.

PRINCIPAL FINDINGS

The current study demonstrates the antibiofilm activity of 3Furancarboxaldehyde (3FCA), a floral honey derived compound, against GAS biofilm, which was divulged using crystal violet assay, light microscopy, and confocal laser scanning microscopy. The report is extended to study its effect on various aspects of GAS (morphology, virulence, aggregation) at its minimal biofilm inhibitory concentration (132μg/ml). 3FCA was found to alter the growth pattern of GAS in solid and liquid medium and increased the rate of auto-aggregation. Electron microscopy unveiled the increase in extra polymeric substances around cell. Gene expression studies showed down-regulation of covR gene, which is speculated to be the prime target for the antibiofilm activity. Increased hyaluronic acid production and down regulation of srtB gene is attributed to the enhanced rate of auto-aggregation. The virulence genes (srv, mga, luxS and hasA) were also found to be over expressed, which was manifested with the increased susceptibility of the model organism Caenorhabditis elegans to 3FCA treated GAS. The toxicity of 3FCA was ruled out with no adverse effect on C. elegans.

SIGNIFICANCE

Though 3FCA possess antibiofilm activity against GAS, it was also found to increase the virulence of GAS. This study demonstrates that, covR mediated antibiofilm activity may increase the virulence of GAS. This also emphasizes the importance to analyse the acclimatization response and virulence of the pathogen in the presence of antibiofilm compounds prior to their clinical trials.

Mechanisms of group A Streptococcus resistance to reactive oxygen species

Streptococcus pyogenes, also known as group A Streptococcus (GAS), is an exclusively human Gram-positive bacterial pathogen ranked among the ‘top 10’ causes of infection-related deaths worldwide. GAS commonly causes benign and self-limiting epithelial infections (pharyngitis and impetigo), and less frequent severe invasive diseases (bacteremia, toxic shock syndrome and necrotizing fasciitis). Annually, GAS causes 700 million infections, including 1.8 million invasive infections with a mortality rate of 25%. In order to establish an infection, GAS must counteract the oxidative stress conditions generated by the release of reactive oxygen species (ROS) at the infection site by host immune cells such as neutrophils and monocytes. ROS are the highly reactive and toxic byproducts of oxygen metabolism, including hydrogen peroxide (H₂O₂), superoxide anion (O₂•⁻), hydroxyl radicals (OH•) and singlet oxygen (O₂*), which can damage bacterial nucleic acids, proteins and cell membranes. This review summarizes the enzymatic and regulatory mechanisms utilized by GAS to thwart ROS and survive under conditions of oxidative stress.

This review discusses the mechanisms utilized by the bacterial pathogen group A Streptococcus to detoxify reactive oxygen species and survive in the human host under conditions of oxidative stress.