Growth phase-dependent modulation of Rgg binding specificity in Streptococcus pyogenes

Ag2[Fe(CN)5NO]-Fabricated Hydrophobic Cotton as a Potential Wound Healing Dressing: An In Vivo Approach

There have been reports of different types of wound dressings for various functions and purposes. Cotton being one of the most widely used wound dressing material due to its non-toxic, biodegradable, and other properties is used for fabrication as well as in the form of scaffolds for faster and effective wound closure. Our research team has already demonstrated the role of silver nitroprusside nanoparticles (SNPNPs) for wound healing and antibacterial activity. In the current study, we have developed cotton fabric impregnated with SNPNPs (SNPCFs) which remain photo inert and displayed long-term antimicrobial activity due to the surface modification with the silver nitroprusside complex. These SNPCFs were characterized by various analytical techniques (XRD, FTIR, UV spectroscopy, TGA, TEM, FESEM, EDAX, ICP-OES). The fabricated cotton dressings with nanoparticles showed an improved water contact angle (113-130°) than that of bare cotton gauze (60°) and exhibited more antibacterial property in case of both Gram-negative bacteria (Klebsiella aerogenes and Escherichia coli) and Gram-positive bacteria (Pseudomonas aeruginosa and Bacillus subtilis) even after several washings. The biocompatible nature of SNPCFs was assessed by in vivo chorioallantoic membrane assay that showed no obstruction in the formation of blood vessels. The SNPCFs exhibited better wound healing activity compared to the bare cotton and AgCFs as observed in the C57BL6/J mouse. The histopathological investigation reveals increase in re-epithelialization and deposition of connective tissue. The macrophage (M2) counts in SNPCF-treated skin tissues were supportive of more wound healing activity than mice treated with cotton fabric impregnated with chemically synthesized silver nanoparticles. Based on biodistribution analysis using ICP-OES, the data illustrated that a significant amount of silver is absorbed in the skin tissues of mice as compared to the blood and kidney. Furthermore, the absence of silver from the vital organs (heart, liver, and kidney) corroborates our hypothesis that the SNPCFs can act excellently in treating wounds when topically applied over skin. Thereafter, all these results highlight a strong possibility that SNPCFs exemplify the potential as a new antimicrobial and wound healing agent in future times.

Endopeptidase PepO Regulates the SpeB Cysteine Protease and Is Essential for the Virulence of Invasive M1T1 Streptococcus pyogenes

Streptococcus pyogenes (group A Streptococcus [GAS]) causes a wide range of human infections. The pathogenesis of GAS infections is dependent on the temporal expression of numerous secreted and surface-associated virulence factors that interact with host proteins. Streptococcal pyrogenic exotoxin B (SpeB) is one of the most extensively studied toxins produced by GAS, and the coordinate growth phase-dependent regulation of speB expression is linked to disease severity phenotypes. Here, we identified the endopeptidase PepO as a novel growth phase-dependent regulator of SpeB in the invasive GAS M1 serotype strain 5448. By using transcriptomics followed by quantitative reverse transcriptase PCR and Western blot analyses, we demonstrate through targeted mutagenesis that PepO influences growth phase-dependent induction of speB gene expression. Compared to wild-type and complemented mutant strains, we demonstrate that the 5448ΔpepO mutant strain is more susceptible to killing by human neutrophils and is attenuated in virulence in a murine model of invasive GAS infection. Our results expand the complex regulatory network that is operating in GAS to control SpeB production and suggest that PepO is a virulence requirement during GAS M1T1 strain 5448 infections.IMPORTANCE Despite the continuing susceptibility of S. pyogenes to penicillin, this bacterial pathogen remains a leading infectious cause of global morbidity and mortality. A particular subclone of the M1 serotype (M1T1) has persisted globally for decades as the most frequently isolated serotype from patients with invasive and noninvasive diseases in Western countries. One of the key GAS pathogenicity factors is the potent broad-spectrum cysteine protease SpeB. Although there has been extensive research interest on the regulatory mechanisms that control speB gene expression, its genetic regulation is not fully understood. Here, we identify the endopeptidase PepO as a new regulator of speB gene expression in the globally disseminated M1T1 clone and as being essential for virulence.

Interference of a speB 5' untranslated region partial deletion with mRNA degradation in Streptococcus pyogenes

The 5' untranslated region (5' UTR) of an mRNA molecule embeds important determinants that modify its stability and translation efficiency. In Streptococcus pyogenes, a strict human pathogen, a gene encoding a secreted protease (speB) has a large 5' UTR with unknown functions. Here we describe that a partial deletion of the speB 5' UTR caused a general accumulation of mRNA in the stationary phase, and that the mRNA accumulation was due to retarded mRNA degradation. The phenotype was observed in several M serotypes harboring the partial deletion of the speB 5' UTR. The phenotype was triggered by the production of the truncated speB 5' UTR, but not by the disruption of the intact speB 5' UTR. RNase Y, a major endoribonuclease, was previously shown to play a central role in bulk mRNA turnover in stationary phase. However, in contrast to our expectations, we observed a weaker interaction between the truncated speB 5' UTR and RNase Y compared with the wild-type, which suggests that other unidentified RNA degrading components are required for the pleiotropic effects observed from the speB UTR truncation. Our study demonstrates how S. pyogenes uses distinct mRNA degradation schemes in exponential and stationary growth phases.

Repression of Rgg But Not Upregulation of LacD.1 in emm1-type covS Mutant Mediates the SpeB Repression in Group A Streptococcus

CovR/CovS is an important two-component regulatory system in human pathogen group A Streptococcus (GAS). Epidemiological studies have shown that inactivation of the sensor kinase CovS is correlated with invasive clinical manifestations. The phosphorylation level of response regulator CovR decreases dramatically in the absence of CovS, resulting in the derepression of virulence factor expression and an increase in bacterial invasiveness. Streptococcal pyrogenic exotoxin B (SpeB) is a cysteine protease and is negatively regulated by CovR; however, the expression of SpeB is almost completely repressed in the covS mutant. The present study found that in the emm1-type A20 strain, non-phosphorylated CovR acts as a transcriptional repressor for SpeB-positive regulator Rgg. In addition, the expression of Rgg-negative regulator LacD.1 is upregulated in the covS mutant. These results suggest that inactivation of Rgg in the covS mutant would directly mediate speB repression. The current study showed that overexpression of rgg but not inactivation of lacD.1 in the covS mutant partially restores speB expression, indicating that only rgg repression, but not lacD.1 upregulation, contributes to the speB repression in the covS mutant.

Molecular epidemiology and genomics of group A Streptococcus

Streptococcus pyogenes (group A Streptococcus; GAS) is a strict human pathogen with a very high prevalence worldwide. This review highlights the genetic organization of the species and the important ecological considerations that impact its evolution. Recent advances are presented on the topics of molecular epidemiology, population biology, molecular basis for genetic change, genome structure and genetic flux, phylogenomics and closely related streptococcal species, and the long- and short-term evolution of GAS. The application of whole genome sequence data to addressing key biological questions is discussed.

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.

Unique genomic arrangements in an invasive serotype M23 strain of Streptococcus pyogenes identify genes that induce hypervirulence

The first genome sequence of a group A Streptococcus pyogenes serotype M23 (emm23) strain (M23ND), isolated from an invasive human infection, has been completed. The genome of this opacity factor-negative (SOF(-)) strain is composed of a circular chromosome of 1,846,477 bp. Gene profiling showed that this strain contained six phage-encoded and 24 chromosomally inherited well-known virulence factors, as well as 11 pseudogenes. The bacterium has acquired four large prophage elements, ΦM23ND.1 to ΦM23ND.4, harboring genes encoding streptococcal superantigen (ssa), streptococcal pyrogenic exotoxins (speC, speH, and speI), and DNases (spd1 and spd3), with phage integrase genes being present at one flank of each phage insertion, suggesting that the phages were integrated by horizontal gene transfer. Comparative analyses revealed unique large-scale genomic rearrangements that result in genomic rearrangements that differ from those of previously sequenced GAS strains. These rearrangements resulted in an imbalanced genomic architecture and translocations of chromosomal virulence genes. The covS sensor in M23ND was identified as a pseudogene, resulting in the attenuation of speB function and increased expression of the genes for the chromosomal virulence factors multiple-gene activator (mga), M protein (emm23), C5a peptidase (scpA), fibronectin-binding proteins (sfbI and fbp54), streptolysin O (slo), hyaluronic acid capsule (hasA), streptokinase (ska), and DNases (spd and spd3), which were verified by PCR. These genes are responsible for facilitating host epithelial cell binding and and/or immune evasion, thus further contributing to the virulence of M23ND. In conclusion, strain M23ND has become highly pathogenic as the result of a combination of multiple genetic factors, particularly gene composition and mutations, prophage integrations, unique genomic rearrangements, and regulated expression of critical virulence factors.

Quorum sensing in group A Streptococcus

Quorum sensing (QS) is a widespread phenomenon in the microbial world that has important implications in the coordination of population-wide responses in several bacterial pathogens. In Group A Streptococcus (GAS), many questions surrounding QS systems remain to be solved pertaining to their function and their contribution to the GAS lifestyle in the host. The QS systems of GAS described to date can be categorized into four groups: regulator gene of glucosyltransferase (Rgg), Sil, lantibiotic systems, and LuxS/AI-2. The Rgg family of proteins, a conserved group of transcription factors that modify their activity in response to signaling peptides, has been shown to regulate genes involved in virulence, biofilm formation and competence. The sil locus, whose expression is regulated by the activity of signaling peptides and a putative two-component system (TCS), has been implicated on regulating genes involved with invasive disease in GAS isolates. Lantibiotic regulatory systems are involved in the production of bacteriocins and their autoregulation, and some of these genes have been shown to target both bacterial organisms as well as processes of survival inside the infected host. Finally AI-2 (dihydroxy pentanedione, DPD), synthesized by the LuxS enzyme in several bacteria including GAS, has been proposed to be a universal bacterial communication molecule. In this review we discuss the mechanisms of these four systems, the putative functions of their targets, and pose critical questions for future studies.

Cloning, purification, crystallization and preliminary X-ray studies of the putative transcriptional regulator SPD0280 from Streptococcus pneumoniae D39

Streptococcus pneumoniae SPD0280 is a hypothetical protein that has been putatively identified as a transcriptional regulator. However, it has very low sequence identity to other well characterized transcriptional regulators. Determination of the three-dimensional structure may provide information for the characterization of proteins; therefore, it was decided to use X-ray diffraction analysis to learn more about this protein. Here, the expression, purification, crystallization and preliminary crystallographic analysis of SPD0280 from S. pneumoniae are reported. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 45.886, b = 66.785, c = 150.050 Å, and diffracted to a resolution of 2.5 Å. The crystals are likely to contain one molecule in the asymmetric unit, with a VM value of 2.06 Å(3) Da(-1).

Bacterial Adhesion of Streptococcus suis to Host Cells and Its Inhibition by Carbohydrate Ligands

Streptococcus suis is a Gram-positive bacterium, which causes sepsis and meningitis in pigs and humans. This review examines the role of known S. suis virulence factors in adhesion and S. suis carbohydrate-based adhesion mechanisms, as well as the inhibition of S. suis adhesion by anti-adhesion compounds in in vitro assays. Carbohydrate-binding specificities of S. suis have been identified, and these studies have shown that many strains recognize Galα1-4Gal-containing oligosaccharides present in host glycolipids. In the era of increasing antibiotic resistance, new means to treat infections are needed. Since microbial adhesion to carbohydrates is important to establish disease, compounds blocking adhesion could be an alternative to antibiotics. The use of oligosaccharides as drugs is generally hampered by their relatively low affinity (micromolar) to compete with multivalent binding to host receptors. However, screening of a library of chemically modified Galα1-4Gal derivatives has identified compounds that inhibit S. suis adhesion in nanomolar range. Also, design of multivalent Galα1-4Gal-containing dendrimers has resulted in a significant increase of the inhibitory potency of the disaccharide. The S. suis adhesin binding to Galα1-4Gal-oligosaccharides, Streptococcal adhesin P (SadP), was recently identified. It has a Galα1-4Gal-binding N-terminal domain and a C-terminal LPNTG-motif for cell wall anchoring. The carbohydrate-binding domain has no homology to E. coli P fimbrial adhesin, which suggests that these Gram-positive and Gram-negative bacterial adhesins recognizing the same receptor have evolved by convergent evolution. SadP adhesin may represent a promising target for the design of anti-adhesion ligands for the prevention and treatment of S. suis infections.

Transcriptional regulation of a bacteriophage encoded extracellular DNase (Spd-3) by Rgg in Streptococcus pyogenes

The Streptococcus pyogenes transcriptional regulator Rgg controls the expression of virulence-associated genes encoded both within the core genome and within horizontally transmissible DNA such as temperate bacteriophage. Previously, we showed that Rgg binds to the non-coding DNA upstream of the bacteriophage gene encoding an extracellular DNase Spd-3. In the current study, we further characterized Rgg-mediated regulation of spd-3 expression. Two spd-3 transcripts were identified by northern blotting. The 5′ ends were 27 and 594 nucleotides upstream of the start codon as determined with primer extension analysis and 5′ RACE (rapid amplification of c-DNA ends), respectively. Results obtained with gel shift assays showed that purified Rgg bound specifically to non-coding DNA containing the promoters of both transcripts. Transcriptional fusion analyses confirmed the presence of Rgg-repressible promoters within these DNA regions. In addition, repression was associated with direct DNA binding by Rgg as determined with chromatin immunoprecipitation (ChIP) coupled with quantitative PCR (qPCR). The results show that the chromosomally encoded transcriptional regulator, Rgg, directly represses both bacteriophage promoters controlling the expression of Spd-3. The results provide new information regarding the regulation of prophage encoded virulence factors of S. pyogenes and highlight the complex evolutionary history of S. pyogenes and temperate bacteriophage.

Adaptive evolution of the Streptococcus pyogenes regulatory aldolase LacD.1

In the human-pathogenic bacterium Streptococcus pyogenes, the tagatose bisphosphate aldolase LacD.1 likely originated through a gene duplication event and was adapted to a role as a metabolic sensor for regulation of virulence gene transcription. Although LacD.1 retains enzymatic activity, its ancestral metabolic function resides in the LacD.2 aldolase, which is required for the catabolism of galactose. In this study, we compared these paralogous proteins to identify characteristics correlated with divergence and novel function. Surprisingly, despite the fact that these proteins have identical active sites and 82% similarity in amino acid sequence, LacD.1 was less efficient at cleaving both fructose and tagatose bisphosphates. Analysis of kinetic properties revealed that LacD.1's adaptation was associated with a decrease in k(cat) and an increase in K(m). Construction and analysis of enzyme chimeras indicated that non-active-site residues previously associated with the variable activities of human aldolase isoenzymes modulated LacD.1's affinity for substrate. Mutant LacD.1 proteins engineered to have LacD.2-like levels of enzymatic efficiency lost the ability to function as regulators, suggesting that an alteration in efficiency was required for adaptation. In competition under growth conditions that mimic a deep-tissue environment, LacD.1 conferred a significant gain in fitness that was associated with its regulatory activity. Taken together, these data suggest that LacD.1's adaptation represents a form of neofunctionalization in which duplication facilitated the gain of regulatory function important for growth in tissue and pathogenesis.