Murine vaginal colonization model for investigating asymptomatic mucosal carriage of Streptococcus pyogenes

Engineered probiotic overcomes pathogen defences using signal interference and antibiotic production to treat infection in mice

Probiotic supplements are suggested to promote human health by preventing pathogen colonization. However, the mechanistic bases for their efficacy in vivo are largely uncharacterized. Here using metabolomics and bacterial genetics, we show that the human oral probiotic Streptococcus salivarius K12 (SAL) produces salivabactin, an antibiotic that effectively inhibits pathogenic Streptococcus pyogenes (GAS) in vitro and in mice. However, prophylactic dosing with SAL enhanced GAS colonization in mice and ex vivo in human saliva. We showed that, on co-colonization, GAS responds to a SAL intercellular peptide signal that controls SAL salivabactin production. GAS produces a secreted protease, SpeB, that targets SAL-derived salivaricins and enhances GAS survival. Using this knowledge, we re-engineered probiotic SAL to prevent signal eavesdropping by GAS and potentiate SAL antimicrobials. This engineered probiotic demonstrated superior efficacy in preventing GAS colonization in vivo. Our findings show that knowledge of interspecies interactions can identify antibiotic- and probiotic-based strategies to combat infection.

Studies of Streptococcus anginosus Virulence in Dictyostelium discoideum and Galleria mellonella Models

For many years, Streptococcus anginosus has been considered a commensal colonizing the oral cavity, as well as the gastrointestinal and genitourinary tracts. However, recent epidemiological and clinical data designate this bacterium as an emerging opportunistic pathogen. Despite the reported pathogenicity of S. anginosus, the molecular mechanism underpinning its virulence is poorly described. Therefore, our goal was to develop and optimize efficient and simple infection models that can be applied to examine the virulence of S. anginosus and to study host-pathogen interactions. Using 23 S. anginosus isolates collected from different infections, including severe and superficial infections, as well as an attenuated strain devoid of CppA, we demonstrate for the first time that Dictyostelium discoideum is a suitable model for initial, fast, and large-scale screening of virulence. Furthermore, we found that another nonvertebrate animal model, Galleria mellonella, can be used to study the pathogenesis of S. anginosus infection, with an emphasis on the interactions between the pathogen and host innate immunity. Examining the profile of immune defense genes, including antimicrobial peptides, opsonins, regulators of nodulation, and inhibitors of proteases, by quantitative PCR (qPCR) we identified different immune response profiles depending on the S. anginosus strain. Using these models, we show that S. anginosus is resistant to the bactericidal activity of phagocytes, a phenomenon confirmed using human neutrophils. Notably, since we found that the data from these models corresponded to the clinical severity of infection, we propose their further application to studies of the virulence of S. anginosus.

The Integrative Conjugative Element ICESpyM92 Contributes to Pathogenicity of Emergent Antimicrobial-Resistant emm92 Group A Streptococcus

Antimicrobial resistance-encoding mobile genetic elements (MGEs) may contribute to the disease potential of bacterial pathogens. We previously described the association of Group A Streptococcus (GAS) derived from invasive disease with increasingly frequent antimicrobial resistance (AMR). We hypothesized that a 65-kb AMR-encoding MGE (ICESpyM92), highly conserved among closely related emergent invasive emm92 GAS, contributes to GAS disease potential. Here, we provide evidence that a combination of ICESpyM92- and core genome-dependent differential gene expression (DGE) contributes to invasive disease phenotypes of emergent emm92 GAS. Using isogenic ICESpyM92 mutants generated in distinct emm92 genomic backgrounds, we determined the presence of ICESpyM92 enhances GAS virulence in a mouse subcutaneous infection model. Measurement of in vitro and ex vivo DGE indicates ICESpyM92 influences GAS global gene expression in a background-dependent manner. Our study links virulence and AMR on a unique MGE via MGE-related DGE and highlights the importance of investigating associations between AMR-encoding MGEs and pathogenicity.

Influence of the Alternative Sigma Factor RpoN on Global Gene Expression and Carbon Catabolism in Enterococcus faecalis V583

The alternative sigma factor σ⁵⁴ has been shown to regulate the expression of a wide array of virulence-associated genes, as well as central metabolism, in bacterial pathogens. In Gram-positive organisms, the σ⁵⁴ is commonly associated with carbon metabolism. In this study, we show that the Enterococcus faecalis alternative sigma factor σ⁵⁴ (RpoN) and its cognate enhancer binding protein MptR are essential for mannose utilization and are primary contributors to glucose uptake through the Mpt phosphotransferase system. To gain further insight into how RpoN contributes to global transcriptional changes, we performed microarray transcriptional analysis of strain V583 and an isogenic rpoN mutant grown in a chemically defined medium with glucose as the sole carbon source. Transcripts of 340 genes were differentially affected in the rpoN mutant; the predicted functions of these genes mainly related to nutrient acquisition. These differentially expressed genes included those with predicted catabolite-responsive element (cre) sites, consistent with loss of repression by the major carbon catabolite repressor CcpA. To determine if the inability to efficiently metabolize glucose/mannose affected infection outcome, we utilized two distinct infection models. We found that the rpoN mutant is significantly attenuated in both rabbit endocarditis and murine catheter-associated urinary tract infection (CAUTI). Here, we examined a ccpA mutant in the CAUTI model and showed that the absence of carbon catabolite control also significantly attenuates bacterial tissue burden in this model. Our data highlight the contribution of central carbon metabolism to growth of E. faecalis at various sites of infection.

Genome-wide analysis of in vivo CcpA binding with and without its key co-factor HPr in the major human pathogen group A Streptococcus

Catabolite control protein A (CcpA) is a master regulator of carbon source utilization and contributes to the virulence of numerous medically important Gram‐positive bacteria. Most functional assessments of CcpA, including interaction with its key co‐factor HPr, have been performed in nonpathogenic bacteria. In this study we aimed to identify the in vivo DNA binding profile of CcpA and assess the extent to which HPr is required for CcpA‐mediated regulation and DNA binding in the major human pathogen group A Streptococcus (GAS). Using a combination RNAseq/ChIP‐seq approach, we found that CcpA affects transcript levels of 514 of 1667 GAS genes (31%) whereas direct DNA binding was identified for 105 GAS genes. Three of the directly regulated genes encode the key GAS virulence factors Streptolysin S, PrtS (IL‐8 degrading proteinase), and SpeB (cysteine protease). Mutating CcpA Val301 to Ala (strain 2221‐CcpA‐V301A) abolished interaction between CcpA and HPr and impacted the transcript levels of 205 genes (40%) in the total CcpA regulon. By ChIP‐seq analysis, CcpAV301A bound to DNA from 74% of genes bound by wild‐type CcpA, but generally with lower affinity. These data delineate the direct CcpA regulon and clarify the HPr‐dependent and independent activities of CcpA in a key pathogenic bacterium.

A Novel Heme Transporter from the Energy Coupling Factor Family Is Vital for Group A Streptococcus Colonization and Infections

Group A streptococcus (GAS) produces millions of infections worldwide, including mild mucosal infections, postinfection sequelae, and life-threatening invasive diseases. During infection, GAS readily acquires nutritional iron from host heme and hemoproteins. Here, we identified a new heme importer, named SiaFGH, and investigated its role in GAS pathophysiology. The SiaFGH proteins belong to a group of transporters with an unknown ligand from the recently described family of energy coupling factors (ECFs). A siaFGH deletion mutant exhibited high streptonigrin resistance compared to the parental strain, suggesting that iron ions or an iron complex is the likely ligand. Iron uptake and inductively coupled plasma mass spectrometry (ICP-MS) studies showed that the loss of siaFGH did not impact GAS import of ferric or ferrous iron, but the mutant was impaired in using hemoglobin iron for growth. Analysis of cells growing on hemoglobin iron revealed a substantial decrease in the cellular heme content in the mutant compared to the complemented strain. The induction of the siaFGH genes in trans resulted in the induction of heme uptake. The siaFGH mutant exhibited a significant impairment in murine models of mucosal colonization and systemic infection. Together, the data show that SiaFGH is a new type of heme importer that is key for GAS use of host hemoproteins and that this system is imperative for bacterial colonization and invasive infection.IMPORTANCE ECF systems are new transporters that take up various vitamins, cobalt, or nickel with a high affinity. Here, we establish the GAS SiaFGH proteins as a new ECF module that imports heme and demonstrate its importance in virulence. SiaFGH is the first heme ECF system described in bacteria. We identified homologous systems in the genomes of related pathogens from the Firmicutes phylum. Notably, GAS and other pathogens that use a SiaFGH-type importer rely on host hemoproteins for a source of iron during infection. Hence, recognizing the function of this noncanonical ABC transporter in heme acquisition and the critical role that it plays in disease has broad implications.

Dissecting Streptococcus pyogenes interaction with human

Streptococcus pyogenes is a species of Gram-positive bacteria. It is also known as Group A Streptococcus (GAS) that causes pathogenesis to humans only. The GAS infection has several manifestations including invasive illness. Current research has linked the molecular modes of GAS virulence with substantial sequencing determinations for the isolation of genomes. These advances help to comprehend the molecular evolution resulting in the pandemic strains. Thus, it is indispensable to reconsider the philosophy that involves GAS pathogenesis. The recent investigations involve studying GAS in the nasopharynx and its capability to cause infection or asymptomatically reside in the host. These advances have been discussed in this article with an emphasis on the natural history of GAS and the evolutionary change in the pandemic strains. In addition, this review describes the unique functions for major pathogenicity determinants to comprehend their physiological effects.

Invasion of vaginal epithelial cells by uropathogenic Escherichia coli

Host-associated reservoirs account for the majority of recurrent and oftentimes recalcitrant infections. Previous studies established that uropathogenic E. coli - the primary cause of urinary tract infections (UTIs) - can adhere to vaginal epithelial cells preceding UTI. Here, we demonstrate that diverse urinary E. coli isolates not only adhere to, but also invade vaginal cells. Intracellular colonization of the vaginal epithelium is detected in acute and chronic murine UTI models indicating the ability of E. coli to reside in the vagina following UTI. Conversely, in a vaginal colonization model, E. coli are detected inside vaginal cells and the urinary tract, indicating that vaginal colonization can seed the bladder. More critically, bacteria are identified inside vaginal cells from clinical samples from women with a history of recurrent UTI. These findings suggest that E. coli can establish a vaginal intracellular reservoir, where it may reside safely from extracellular stressors prior to causing an ascending infection.

A Mobile Genetic Element Promotes the Association Between Serotype M28 Group A Streptococcus Isolates and Cases of Puerperal Sepsis

BACKGROUND

Bacterial infections following childbirth-so-called puerperal infections-cause morbidity in 5%-10% of all new mothers. At low frequency, the infection can spread to the blood, resulting in life-threatening sepsis known as puerperal sepsis. Pathogens causing puerperal sepsis include group A Streptococcus (GAS), and epidemiological analyses have identified isolates of a single serotype, M28, as being nonrandomly associated with cases of puerperal sepsis. The genomes of serotype M28 GAS isolates harbor a 36.3-kb mobile genetic element of apparent group B Streptococcus origin, termed region of difference 2 (RD2).

METHODS

The phenotypic (determined via tissue culture and a vaginal colonization model) and regulatory (determined via RNA sequencing analysis) contributions of RD2 were assessed by comparing parental, RD2 deletion mutant, and complemented mutant serotype M28 GAS strains.

RESULTS

RD2 affords serotype M28 isolates an enhanced ability to adhere to human vaginal epithelial cells and to colonize the female reproductive tract in a mouse model of infection. In addition, RD2 influences the abundance of messenger RNAs from >100 core chromosomal GAS genes.

CONCLUSIONS

The data are consistent with RD2 directly, via encoded virulence factors, and indirectly, via encoded regulatory proteins, modifying the virulence potential of GAS and contributing to the decades-old association of serotype M28 isolates with cases of puerperal sepsis.

Genome-Wide Screens Identify Group A Streptococcus Surface Proteins Promoting Female Genital Tract Colonization and Virulence

Group A streptococcus (GAS) is a major pathogen that impacts health and economic affairs worldwide. Although the oropharynx is the primary site of infection, GAS can colonize the female genital tract and cause severe diseases, such as puerperal sepsis, neonatal infections, and necrotizing myometritis. Our understanding of how GAS genes contribute to interaction with the primate female genital tract is limited by the lack of relevant animal models. Using two genome-wide transposon mutagenesis screens, we identified 69 GAS genes required for colonization of the primate vaginal mucosa in vivo and 96 genes required for infection of the uterine wall ex vivo. We discovered a common set of 39 genes important for GAS fitness in both environments. They include genes encoding transporters, surface proteins, transcriptional regulators, and metabolic pathways. Notably, the genes that encode the surface-exclusion protein (SpyAD) and the immunogenic secreted protein 2 (Isp2) were found to be crucial for GAS fitness in the female primate genital tract. Targeted gene deletion confirmed that isogenic mutant strains ΔspyAD and Δisp2 are significantly impaired in ability to colonize the primate genital tract and cause uterine wall pathologic findings. Our studies identified novel GAS genes that contribute to female reproductive tract interaction that warrant translational research investigation.

Transcriptomic Analysis of Streptococcus pyogenes Colonizing the Vaginal Mucosa Identifies hupY, an MtsR-Regulated Adhesin Involved in Heme Utilization

Colonization of the host requires the ability to adapt to an environment that is often low in essential nutrients such as iron. Here we present data showing that the transcriptome of the important human pathogen Streptococcus pyogenes shows extensive remodeling during in vivo growth, resulting in, among many other differentially expressed genes and pathways, a significant increase in genes involved in acquiring iron from host heme. Data show that HupY, previously characterized as an adhesin in both S. pyogenes and the related pathogen Streptococcus agalactiae, binds heme and affects intracellular iron concentrations. HupY, a protein with no known heme binding domains, represents a novel heme binding protein playing an important role in bacterial iron homeostasis as well as vaginal colonization.

Streptococcus pyogenes (group A streptococcus [GAS]) is a serious human pathogen with the ability to colonize mucosal surfaces such as the nasopharynx and vaginal tract, often leading to infections such as pharyngitis and vulvovaginitis. We present genome-wide transcriptome sequencing (RNASeq) data showing the transcriptomic changes GAS undergoes during vaginal colonization. These data reveal that the regulon controlled by MtsR, a master metal regulator, is activated during vaginal colonization. This regulon includes two genes highly expressed during vaginal colonization, hupYZ. Here we show that HupY binds heme in vitro, affects intracellular concentrations of iron, and is essential for proper growth of GAS using hemoglobin or serum as the sole iron source. HupY is also important for murine vaginal colonization of both GAS and the related vaginal colonizer and pathogen Streptococcus agalactiae (group B streptococcus [GBS]). These data provide essential information on the link between metal regulation and mucosal colonization in both GAS and GBS.

DNA methylation from a Type I restriction modification system influences gene expression and virulence in Streptococcus pyogenes

DNA methylation is pervasive across all domains of life. In bacteria, the presence of N6-methyladenosine (m6A) has been detected among diverse species, yet the contribution of m6A to the regulation of gene expression is unclear in many organisms. Here we investigated the impact of DNA methylation on gene expression and virulence within the human pathogen Streptococcus pyogenes, or Group A Streptococcus. Single Molecule Real-Time sequencing and subsequent methylation analysis identified 412 putative m6A sites throughout the 1.8 Mb genome. Deletion of the Restriction, Specificity, and Methylation gene subunits (ΔRSM strain) of a putative Type I restriction modification system lost all detectable m6A at the recognition sites and failed to prevent transformation with foreign-methylated DNA. RNA-sequencing identified 20 genes out of 1,895 predicted coding regions with significantly different gene expression. All of the differentially expressed genes were down regulated in the ΔRSM strain relative to the parent strain. Importantly, we found that the presence of m6A DNA modifications affected expression of Mga, a master transcriptional regulator for multiple virulence genes, surface adhesins, and immune-evasion factors in S. pyogenes. Using a murine subcutaneous infection model, mice infected with the ΔRSM strain exhibited an enhanced host immune response with larger skin lesions and increased levels of pro-inflammatory cytokines compared to mice infected with the parent or complemented mutant strains, suggesting alterations in m6A methylation influence virulence. Further, we found that the ΔRSM strain showed poor survival within human neutrophils and reduced adherence to human epithelial cells. These results demonstrate that, in addition to restriction of foreign DNA, gram-positive bacteria also use restriction modification systems to regulate the expression of gene networks important for virulence.

DNA methylation is common among many bacterial species, yet the contribution of DNA methylation to the regulation of gene expression is unclear outside of a limited number of gram-negative species. We characterized sites of DNA methylation throughout the genome of the gram-positive pathogen Streptococcus pyogenes or Group A Streptococcus. We determined that the gene products of a functional restriction modification system are responsible for genome-wide m6A. The mutant strain lacking DNA methylation showed altered gene expression compared to the parent strain, with several genes important for causing human disease down regulated. Furthermore, we showed that the mutant strain lacking DNA methylation exhibited altered virulence properties compared to the parent strain using various models of pathogenesis. The mutant strain was attenuated for both survival within human neutrophils and adherence to human epithelial cells, and was unable to suppress the host immune response in a murine subcutaneous infection model. Together, these results show that bacterial m6A contributes to differential gene expression and influences the ability of Group A Streptococcus to cause disease. DNA methylation is a conserved feature among bacteria and may represent a potential target for intervention in effort to interfere with the ability of bacteria to cause human disease.

Modeling Streptococcus pyogenes Pharyngeal Colonization in the Mouse

Streptococcus pyogenes, or Group A Streptococcus (GAS), is a human-restricted pathogen most commonly found in the posterior oropharynx of the human host. The bacterium is responsible for 600 million annual cases of pharyngitis globally and has been found to asymptomatically colonize the pharynxes of 4-30% of the population. As such, many studies have utilized animals as models in order to decipher bacterial and host elements that contribute to the bacterial-pharyngeal interaction and determine differences between acute infection and asymptomatic colonization. The aim of this review is to first describe both bacterial and host factors that are important for the pharyngeal persistence of GAS in humans, then to detail the bacterial and host factors that are important for colonization in murine model, and finally to compare the two in order to evaluate the strength of murine pharyngeal colonization as a model for the human-GAS pharyngeal interaction.

Hydrogen Peroxide Production of Group A Streptococci (GAS) is emm-Type Dependent and Increased at Low Temperatures

Group A streptococcus (GAS) is an important human pathogen whose clinical isolates differ in their ability to produce hydrogen peroxide (H₂O₂). H₂O₂ is primarily produced by the enzyme lactate oxidase (LctO), an in depth in silico research revealed that all genome-sequenced GAS possess the required gene lctO. The importance of lctO for GAS is underlined by its highly conserved catabolite control element (cre box) as well as its perfect promotor sequence in comparison to the known consensus sequences of the Gram-positive model organism Bacillus subtilis. In this study, we provide further insight in the function and regulation of lactate oxidase by analyzing a large group of clinical GAS isolates. We found that H₂O₂ production increased over time in the late stationary phase; after 4 days of incubation, 5.4% of the isolates showed a positive result at 37 °C, while the rate increased to 16.4% at 20 °C. This correlation between H₂O₂ production and low temperatures suggests additional regulatory mechanisms for lctO besides catabolite control protein A (CcpA) and indicates that lctO might play a role for GAS energy metabolism at sub-body temperatures. Furthermore, we could identify that H₂O₂ production was different among clinical isolates; we could correlate H₂O₂ production to emm-types, indicating that emm-types 6 and 75 had the highest rate of H₂O₂ production. The emm-type- and temperature-dependent H₂O₂ production of clinical GAS isolates might contribute to their different survival strategies.

CcpA Coordinates Growth/Damage Balance for Streptococcus pyogenes Pathogenesis

To achieve maximum fitness, pathogens must balance growth with tissue damage, coordinating metabolism and virulence factor expression. In the gram-positive bacterium Streptococcus pyogenes, the DNA-binding transcriptional regulator Carbon Catabolite Protein A (CcpA) is a master regulator of both carbon catabolite repression and virulence, suggesting it coordinates growth/damage balance. To examine this, two murine models were used to compare the virulence of a mutant lacking CcpA with a mutant expressing CcpA locked into its high-affinity DNA-binding conformation (CcpAT307Y). In models of acute soft tissue infection and of long-term asymptomatic mucosal colonization, both CcpA mutants displayed altered virulence, albeit with distinct growth/damage profiles. Loss of CcpA resulted in a diminished ability to grow in tissue, leading to less damage and early clearance. In contrast, constitutive DNA-binding activity uncoupled the growth/damage relationship, such that high tissue burdens and extended time of carriage were achieved, despite reduced tissue damage. These data demonstrate that growth/damage balance can be actively controlled by the pathogen and implicate CcpA as a master regulator of this relationship. This suggests a model where the topology of the S. pyogenes virulence network has evolved to couple carbon source selection with growth/damage balance, which may differentially influence pathogenesis at distinct tissues.

Genome-wide discovery of novel M1T1 group A streptococcal determinants important for fitness and virulence during soft-tissue infection

The Group A Streptococcus remains a significant human pathogen causing a wide array of disease ranging from self-limiting to life-threatening invasive infections. Epithelium (skin or throat) colonization with progression to the subepithelial tissues is the common step in all GAS infections. Here, we used transposon-sequencing (Tn-seq) to define the GAS 5448 genetic requirements for in vivo fitness in subepithelial tissue. A near-saturation transposon library of the M1T1 GAS 5448 strain was injected subcutaneously into mice, producing suppurative inflammation at 24 h that progressed to prominent abscesses with tissue necrosis at 48 h. The library composition was monitored en masse by Tn-seq and ratios of mutant abundance comparing the output (12, 24 and 48 h) versus input (T₀) mutant pools were calculated for each gene. We identified a total of 273 subcutaneous fitness (scf) genes with 147 genes (55 of unknown function) critical for the M1T1 GAS 5448 fitness in vivo; and 126 genes (53 of unknown function) potentially linked to in vivo fitness advantage. Selected scf genes were validated in competitive subcutaneous infection with parental 5448. Two uncharacterized genes, scfA and scfB, encoding putative membrane-associated proteins and conserved among Gram-positive pathogens, were further characterized. Defined scfAB mutants in GAS were outcompeted by wild type 5448 in vivo, attenuated for lesion formation in the soft tissue infection model and dissemination to the bloodstream. We hypothesize that scfAB play an integral role in enhancing adaptation and fitness of GAS during localized skin infection, and potentially in propagation to other deeper host environments.

The WHO ranks the Group A Streptococcus (GAS) in the top 10 leading causes of morbidity and mortality from infectious diseases worldwide. GAS is a strict human pathogen causing both benign superficial infections as well as life-threatening invasive diseases. All GAS infections begin by colonization of an epithelium (throat or skin) followed by propagation into subepithelial tissues. The genetic requirements for M1T1 GAS 5448 within this niche were interrogated by in vivo transposon sequencing (Tn-seq), identifying 273 subcutaneous fitness (scf) genes with 108 of those previously of “unknown function”. Two yet uncharacterized genes, scfA and scfB, were shown to be critical during GAS 5448 soft tissue infection and dissemination into the bloodstream. Thus, this study improves the functional annotation of the GAS genome, providing new insights into GAS pathophysiology and enhancing the development of novel GAS therapeutics.

Evolutionary Constraints Shaping Streptococcus pyogenes-Host Interactions

Research on the Gram-positive human-restricted pathogen Streptococcus pyogenes (Group A Streptococcus, GAS) has long focused on invasive illness, the most severe manifestations of GAS infection. Recent advances in descriptions of molecular mechanisms of GAS virulence, coupled with massive sequencing efforts to isolate genomes, have allowed the field to better understand the molecular and evolutionary changes leading to pandemic strains. These findings suggest that it is necessary to rethink the dogma involving GAS pathogenesis, and that the most productive avenues for research going forward may be investigations into GAS in its 'normal' habitat, the nasopharynx, and its ability to either live with its host in an asymptomatic lifestyle or as an agent of superficial infections. This review will consider these advances, focusing on the natural history of GAS, the evolution of pandemic strains, and novel roles for several key virulence factors that may allow the field to better understand their physiological role.

Stress Physiology of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance.

Interleukin-17A Contributes to the Control of Streptococcus pyogenes Colonization and Inflammation of the Female Genital Tract

Postpartum women are at increased risk of developing puerperal sepsis caused by group A Streptococcus (GAS). Specific GAS serotypes, including M1 and M28, are more commonly associated with puerperal sepsis. However, the mechanisms of GAS genital tract infection are not well understood. We utilized a murine genital tract carriage model to demonstrate that M1 and M28 GAS colonization triggers TNF-α, IL-1β, and IL-17A production in the female genital tract. GAS-induced IL-17A significantly influences streptococcal carriage and alters local inflammatory responses in two genetically distinct inbred strains of mice. An absence of IL-17A or the IL-1 receptor was associated with reduced neutrophil recruitment to the site of infection; and clearance of GAS was significantly attenuated in IL-17A(-/-) mice and Rag1(-/-) mice (that lack mature lymphocytes) but not in mice deficient for the IL-1 receptor. Together, these findings support a role for IL-17A in contributing to the control of streptococcal mucosal colonization and provide new insight into the inflammatory mediators regulating host-pathogen interactions in the female genital tract.

Complete Genome Sequence of emm28 Type Streptococcus pyogenes MEW123, a Streptomycin-Resistant Derivative of a Clinical Throat Isolate Suitable for Investigation of Pathogenesis

We present here the complete genome sequence of Streptococcus pyogenes type emm28 strain MEW123, a streptomycin-resistant derivative of a pediatric throat isolate. The genome length is 1,878,699 bp, with 38.29% G+C% content. The genome sequence adds value to this virulent emm28 representative strain and will aid in the investigation of streptococcal pathogenesis.

Elimination of Chromosomal Island SpyCIM1 from Streptococcus pyogenes Strain SF370 Reverses the Mutator Phenotype and Alters Global Transcription

Streptococcus pyogenes chromosomal island M1 (SpyCIM1) integrates by site-specific recombination into the 5’ end of DNA mismatch repair (MMR) gene mutL in strain SF370SmR, blocking transcription of it and the downstream operon genes. During exponential growth, SpyCIM1 excises from the chromosome and replicates as an episome, restoring mutL transcription. This process is reversed in stationary phase with SpyCIM1 re-integrating into mutL, returning the cells to a mutator phenotype. Here we show that elimination of SpyCIM1 relieves this mutator phenotype. The downstream MMR operon genes, multidrug efflux pump lmrP, Holliday junction resolution helicase ruvA, and DNA base excision repair glycosylase tag, are also restored to constitutive expression by elimination of SpyCIM1. The presence of SpyCIM1 alters global transcription patterns in SF370SmR. RNA sequencing (RNA-Seq) demonstrated that loss of SpyCIM1 in the SpyCIM1 deletion mutant, CEM1Δ4, impacted the expression of over 100 genes involved in virulence and metabolism both in early exponential phase, when the SpyCIM1 is episomal, as well as at the onset of stationary phase, when SpyCIM1 has reintegrated into mutL. Among these changes, the up-regulation of the genes for the antiphagocytic M protein (emm1), streptolysin O (slo), capsule operon (hasABC), and streptococcal pyrogenic exotoxin (speB), are particularly notable. The expression pattern of the MMR operon confirmed our earlier observations that these genes are transcribed in early exponential phase but silenced as stationary phase is approached. Thus, the direct role of SpyCIM1 in causing the mutator phenotype is confirmed, and further, its influence upon the biology of S. pyogenes was found to impact multiple genes in addition to the MMR operon, which is a novel function for a mobile genetic element. We suggest that such chromosomal islands are a remarkable evolutionary adaptation to promote the survival of its S. pyogenes host cell in changing environments.

Streptococcus pyogenes malate degradation pathway links pH regulation and virulence

The ability of Streptococcus pyogenes to infect different niches within its human host most likely relies on its ability to utilize alternative carbon sources. In examining this question, we discovered that all sequenced S. pyogenes strains possess the genes for the malic enzyme (ME) pathway, which allows malate to be used as a supplemental carbon source for growth. ME is comprised of four genes in two adjacent operons, with the regulatory two-component MaeKR required for expression of genes encoding a malate permease (maeP) and malic enzyme (maeE). Analysis of transcription indicated that expression of maeP and maeE is induced by both malate and low pH, and induction in response to both cues is dependent on the MaeK sensor kinase. Furthermore, both maePE and maeKR are repressed by glucose, which occurs via a CcpA-independent mechanism. Additionally, malate utilization requires the PTS transporter EI enzyme (PtsI), as a PtsI(-) mutant fails to express the ME genes and is unable to utilize malate. Virulence of selected ME mutants was assessed in a murine model of soft tissue infection. MaeP(-), MaeK(-), and MaeR(-) mutants were attenuated for virulence, whereas a MaeE(-) mutant showed enhanced virulence compared to that of the wild type. Taken together, these data show that ME contributes to S. pyogenes' carbon source repertory, that malate utilization is a highly regulated process, and that a single regulator controls ME expression in response to diverse signals. Furthermore, malate uptake and utilization contribute to the adaptive pH response, and ME can influence the outcome of infection.

Inactivation of the Rgg2 transcriptional regulator ablates the virulence of Streptococcus pyogenes

Streptococcus pyogenes adapts to different niches encountered in the human host via the activity of numerous regulatory proteins including the Rgg family of transcriptional regulators. The S. pyogenes chromosome encodes four Rgg paralogues designated Rgg1 (RopB), Rgg2 (MutR), Rgg3, and Rgg4 (ComR). In order to understand the role of the Rgg2 protein in the regulation of metabolic and virulence-associated properties of S. pyogenes, the rgg2 gene was inactivated in the M1 serotype strain SF370. Inactivation of rgg2 increased the growth yield of S. pyogenes in THY broth, increased biofilm formation, and increased production of SIC, which is an important virulence factor that inhibits complement mediated lysis. To identify Rgg2-regulated genes, the transcriptomes of SF370 and the rgg2 mutant strains were compared in the middle-exponential and post-exponential phases of growth. Rgg2 was found to control the expression of dozens of genes primarily in the exponential phase of growth, including genes associated with virulence (sse, scpA, slo, nga, mf-3), DNA transformation, and nucleotide metabolism. Inactivation of rgg2 decreased the ability of S. pyogenes to adhere to epithelial cells. In addition, the mutant strain was more sensitive to killing when incubated with human blood and avirulent in a murine bacteremia model. Finally, inoculation of mice with the avirulent rgg2 mutant of S. pyogenes SF370 conferred complete protection to mice subsequently challenged with the wild-type strain. Restoration of an intact rgg2 gene in mutant strain restored the wild-type phenotypes. Overall, the results demonstrate that Rgg2 is an important regulatory protein in S. pyogenes involved in controlling genes associated with both metabolism and virulence.

Analysis of two-component systems in group B Streptococcus shows that RgfAC and the novel FspSR modulate virulence and bacterial fitness

Group B Streptococcus (GBS), in the transition from commensal organisms to pathogens, will encounter diverse host environments and, thus, require coordinated control of the transcriptional responses to these changes. This work was aimed at better understanding the role of two-component signal transduction systems (TCS) in GBS pathophysiology through a systematic screening procedure. We first performed a complete inventory and sensory mechanism classification of all putative GBS TCS by genomic analysis. Five TCS were further investigated by the generation of knockout strains, and in vitro transcriptome analysis identified genes regulated by these systems, ranging from 0.1% to 3% of the genome. Interestingly, two sugar phosphotransferase systems appeared to be differentially regulated in the TCS-16 knockout strain (TCS loci were numbered in order of their appearance on the chromosome), suggesting an involvement in monitoring carbon source availability. High-throughput analysis of bacterial growth on different carbon sources showed that TCS-16 was necessary for the growth of GBS on fructose-6-phosphate. Additional transcriptional analysis provided further evidence for a stimulus-response circuit where extracellular fructose-6-phosphate leads to autoinduction of TCS-16, with concomitant dramatic upregulation of the adjacent operon, which encodes a phosphotransferase system. The TCS-16-deficient strain exhibited decreased persistence in a model of vaginal colonization. All mutant strains were also characterized in a murine model of systemic infection, and inactivation of TCS-17 (also known as RgfAC) resulted in hypervirulence. Our data suggest a role for the previously unknown TCS-16, here named FspSR, in bacterial fitness and carbon metabolism during host colonization, and the data also provide experimental evidence for TCS-17/RgfAC involvement in virulence.

Two-component systems have been evolved by bacteria to detect environmental changes, and they play key roles in pathogenicity. A comprehensive analysis of TCS in GBS has not been performed previously. In this work, we classify 21 TCS and present evidence for the involvement of two specific TCS in GBS virulence and colonization in vivo. Although pinpointing specific TCS stimuli is notoriously difficult, we used a combination of techniques to identify two systems with different effects on GBS pathogenesis. For one of the systems, we propose that fructose-6-phosphate, a metabolite in glycolysis, is sufficient to induce a regulatory response involving a sugar transport system. Our catalogue and classification of TCS may guide further studies into the role of TCS in GBS pathogenicity and biology.

Streptococcus pyogenes arginine and citrulline catabolism promotes infection and modulates innate immunity

A bacterium's ability to acquire nutrients from its host during infection is an essential component of pathogenesis. For the Gram-positive pathogen Streptococcus pyogenes, catabolism of the amino acid arginine via the arginine deiminase (ADI) pathway supplements energy production and provides protection against acid stress in vitro. Its expression is enhanced in murine models of infection, suggesting an important role in vivo. To gain insight into the function of the ADI pathway in pathogenesis, the virulence of mutants defective in each of its enzymes was examined. Mutants unable to use arginine (ΔArcA) or citrulline (ΔArcB) were attenuated for carriage in a murine model of asymptomatic mucosal colonization. However, in a murine model of inflammatory infection of cutaneous tissue, the ΔArcA mutant was attenuated but the ΔArcB mutant was hyperattenuated, revealing an unexpected tissue-specific role for citrulline metabolism in pathogenesis. When mice defective for the arginine-dependent production of nitric oxide (iNOS(-/-)) were infected with the ΔArcA mutant, cutaneous virulence was rescued, demonstrating that the ability of S. pyogenes to utilize arginine was dispensable in the absence of nitric oxide-mediated innate immunity. This work demonstrates the importance of arginine and citrulline catabolism and suggests a novel mechanism of virulence by which S. pyogenes uses its metabolism to modulate innate immunity through depletion of an essential host nutrient.

Complete Genome Sequence of emm Type 14 Streptococcus pyogenes Strain HSC5

Streptococcus pyogenes causes a greater diversity of human disease than any other bacterial pathogen. Here, we present the complete genome sequence of the emm type 14 S. pyogenes strain HSC5. This strain is a robust producer of the cysteine protease SpeB and is capable of producing infection in several different animal models.