ABSTRACT
Staphylococcus aureus is a Gram-positive commensal that can also cause a variety of infections in humans. S. aureus virulence factor gene expression is under tight control by a complex regulatory network, which includes, sigma factors, sRNAs, and two-component systems (TCS). Previous work in our laboratory demonstrated that overexpression of the sRNA tsr37 leads to an increase in bacterial aggregation. Here, we demonstrate that the clumping phenotype is dependent on a previously unannotated 88 amino acid protein encoded within the tsr37 sRNA transcript (which we named ScrA for S. aureus clumping regulator A). To investigate the mechanism of action of ScrA we performed proteomics and transcriptomics in a ScrA overexpressing strain and show that a number of surface adhesins are upregulated, while secreted proteases are downregulated. Results also showed upregulation of the SaeRS TCS, suggesting that ScrA is influencing SaeRS activity. Overexpression of ScrA in a saeR mutant abrogates the clumping phenotype confirming that ScrA functions via the Sae system. Finally, we identified the ArlRS TCS as a positive regulator of scrA expression. Collectively, our results show that ScrA is an activator of the SaeRS system and suggests that ScrA may act as an intermediary between the ArlRS and SaeRS systems.
Subject(s)
RNA, Small Untranslated , Staphylococcal Infections , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Gene Expression , Gene Expression Regulation, Bacterial/genetics , Humans , Protein Kinases/metabolism , RNA, Small Untranslated/metabolism , Staphylococcus aureus/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , Virulence/geneticsABSTRACT
Previously, our group demonstrated a role for the small RNA (sRNA) Teg41 in regulating production of the alpha phenol-soluble modulin toxins (αPSMs) in Staphylococcus aureus. Overexpressing Teg41 increased αPSM production while deleting the 3' end of Teg41 (Teg41Δ3' strain) resulted in a decrease in αPSM production, reduced hemolytic activity of S. aureus culture supernatants, and attenuated virulence in a murine abscess model of infection. In this study, we further explore the attenuation of virulence in the Teg41Δ3' strain. Using both localized and systemic models of infection, we demonstrate that the Teg41Δ3' strain is more severely attenuated than an ΔαPSM mutant, strongly suggesting that Teg41 influences more than the αPSMs. Proteomic and transcriptomic analysis of the wild-type and Teg41Δ3' strains reveals widespread alterations in transcript abundance and protein production in the absence of Teg41, confirming that Teg41 has pleiotropic effects in the cell. We go on to investigate the molecular mechanism underlying Teg41-mediated gene regulation. Surprisingly, results demonstrate that certain Teg41 target genes, including the αPSMs and ßPSMs, are transcriptionally altered in the Teg41Δ3' strain, while other targets, specifically spa (encoding surface protein A), are regulated at the level of transcript stability. Collectively, these data demonstrate that Teg41 is a pleiotropic RNA regulator in S. aureus that influences expression of a variety of genes using multiple different mechanisms.
Subject(s)
Staphylococcal Infections , Staphylococcus aureus , Mice , Animals , Virulence , RNA/metabolism , Proteomics , Gene Expression Regulation, Bacterial , Virulence Factors/genetics , Virulence Factors/metabolism , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Staphylococcal Infections/metabolismABSTRACT
Peptidyl-prolyl cis/trans isomerases (PPIases) are enzymes that assist in protein folding around proline-peptide bonds, and they often possess chaperone activity. Staphylococcus aureus encodes three PPIases, i.e., PrsA, PpiB, and trigger factor (TF). Previous work by our group demonstrated a role for both PrsA and PpiB in S. aureus; however, TF remains largely unstudied. Here, we identify a role for TF in S. aureus biofilm formation and demonstrate cooperation between TF and the cytoplasmic PPIase PpiB. Mutation of the tig gene (encoding TF) led to reduced biofilm development in vitro but no significant attenuation of virulence in a mouse model of infection. To investigate whether TF possesses chaperone activity, we analyzed the ability of a tig mutant to survive acid and base stress. While there was no significant decrease for a tig mutant, a ppiBtig double mutant exhibited significant decreases in cell viability after acid and base challenges. We then demonstrated that a ppiB tig double mutant had exacerbated phenotypes in vitro and in vivo, compared to either single mutant. Finally, in vivo immunoprecipitation of epitope-tagged PpiB revealed that PpiB interacted with 4 times the number of proteins when TF was absent from the cell, suggesting that it may be compensating for the loss of TF. Interestingly, the only proteins found to interact with TF were TF itself, fibronectin-binding protein B (FnBPB), and the chaperone protein ClpB. Collectively, these results support the first phenotype for S. aureus TF and demonstrate a greater network of cooperation between chaperone proteins in Staphylococcus aureusIMPORTANCES. aureus encodes a large number of virulence factors that aid the bacterium in survival and pathogenesis. These virulence factors have a wide variety of functions; however, they must all be properly secreted in order to be functional. Bacterial chaperone proteins often assist in secretion by trafficking proteins to secretion machinery or assisting in proper protein folding. Here, we report that the S. aureus chaperone TF contributes to biofilm formation and cooperates with the chaperone PpiB to regulate S. aureus virulence processes. These data highlight the first known role for TF in S. aureus and suggest that S. aureus chaperone proteins may be involved in a greater regulatory network in the cell.
Subject(s)
Biofilms/growth & development , Gene Expression Regulation, Bacterial/physiology , Peptidylprolyl Isomerase/metabolism , Staphylococcal Infections/microbiology , Staphylococcus aureus/metabolism , Amino Acid Sequence , Animals , Bacterial Proteins , Blood/microbiology , Cell-Free System , Gene Expression Regulation, Enzymologic , Hemolysis , Humans , Mice , Molecular Chaperones , Peptidylprolyl Isomerase/genetics , Staphylococcus aureus/genetics , Staphylococcus aureus/physiologyABSTRACT
A standalone electrochemical method for detecting the bacterium Escherichia coli in water was developed using a nickel electrode and no biorecognition element. Electric current responses from different E. coli concentrations were recorded based on their interaction with a locally formed electrocatalyst. A rotating disk electrode was used to minimize the mass transport limitations at the interface. Results from experiments with the rotating disk electrode also paved the way for hypothesizing the detection mechanism. The operating conditions were established for sensing the electric current responses in the presence of E. coli. The least-squares linear regression model was fit to the data obtained from currents of some known E. coli concentrations. This probe had a detection limit in the order of 104 CFU/ml. The response time to detect the presence/absence of E. coli was less than half a second, while the total assay time, including quantification of its concentration, was 10 min. The electric current response from a solution mixed with E. coli and S. aureus showed current similar to E. coli only solution indicating the specificity of the sensor to respond to signals from E. coli. This electrochemical microbial sensor's uniqueness lies in its ability to rapidly detect E. coli by forming the catalyst locally on demand without the attachment of biorecognition elements.
ABSTRACT
Streptococcus mutans utilizes numerous metabolite transporters to obtain essential nutrients in the "feast or famine" environment of the human mouth. S. mutans and most other streptococci are considered auxotrophic for several essential vitamins including riboflavin (vitamin B2), which is used to generate key cofactors and to perform numerous cellular redox reactions. Despite the well-known contributions of this vitamin to central metabolism, little is known about how S. mutans obtains and metabolizes B2 The uncharacterized protein SMU.1703c displays high sequence homology to the riboflavin transporter RibU. Deletion of SMU.1703c hindered S. mutans growth in complex and defined medium in the absence of saturating levels of exogenous riboflavin, whereas deletion of cotranscribed SMU.1702c alone had no apparent effect on growth. Expression of SMU.1703c in a Bacillus subtilis riboflavin auxotroph functionally complemented growth in nonsaturating riboflavin conditions. S. mutans was also able to grow on flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) in an SMU.1703c-dependent manner. Deletion of SMU.1703c and/or SMU.1702c impacted S. mutans acid stress tolerance, as all mutants showed improved growth at pH 5.5 compared to that of the wild type when medium was supplemented with saturating riboflavin. Cooccurrence of SMU.1703c and SMU.1702c, a hypothetical PAP2 family acid phosphatase gene, appears unique to the streptococci and may suggest a connection of SMU.1702c to the acquisition or metabolism of flavins within this genus. Identification of SMU.1703c as a RibU-like riboflavin transporter furthers our understanding of how S. mutans acquires essential micronutrients within the oral cavity and how this pathogen successfully competes within nutrient-starved oral biofilms.IMPORTANCE Dental caries form when acid produced by oral bacteria erodes tooth enamel. This process is driven by the fermentative metabolism of cariogenic bacteria, most notably Streptococcus mutans Nutrient acquisition is key in the competitive oral cavity, and many organisms have evolved various strategies to procure carbon sources or necessary biomolecules. B vitamins, such as riboflavin, which many oral streptococci must scavenge from the oral environment, are necessary for survival within the competitive oral cavity. However, the primary mechanism and proteins involved in this process remain uncharacterized. This study is important because it identifies a key step in S. mutans riboflavin acquisition and cofactor generation, which may enable the development of novel anticaries treatment strategies via selective targeting of metabolite transporters.
Subject(s)
Operon/physiology , Riboflavin/metabolism , Streptococcus mutans/physiology , Amino Acid Sequence , Computational Biology , Genetic Complementation Test , Humans , Hydrogen-Ion Concentration , Polymerase Chain Reaction/methods , Riboflavin/chemistry , Sequence Alignment , Streptococcus mutans/genetics , Streptococcus mutans/growth & development , Stress, Physiological/geneticsABSTRACT
Extracellular vesicles (EVs) are membrane-derived lipid bilayers secreted by bacteria and eukaryotic cells. Bacterial membrane vesicles were discovered over 60 years ago and have been extensively studied in Gram-negative bacteria. During their production, EVs are loaded with proteins, nucleic acids, and various compounds that are subsequently released into the environment. Depending on the packaged cargo, EVs have a broad spectrum of action and are involved in pathogenesis, antibiotic resistance, nutrient uptake, and nucleic acid transfer. Due to differences in cell wall structure, EVs in Gram-positive bacteria have been disregarded for decades, and our understanding of their biogenesis and host cell interaction is incomplete. Recently, studies on bacteria such as Staphylococcus aureus, Streptococcus spp., Bacillus subtilis, and Mycobacterium spp. have demonstrated EV production in Gram-positive bacteria and shown the great importance EVs have in Gram-positive bacterial physiology and disease progression. Here, we review the latest findings on the biogenesis and functions of EVs from Gram-positive bacteria and identify key areas for future research.
Subject(s)
Extracellular Vesicles/metabolism , Gram-Positive Bacteria/metabolism , Animals , Bacillus subtilis/metabolism , Bioengineering , Biological Transport/genetics , Extracellular Vesicles/chemistry , Extracellular Vesicles/immunology , Gram-Positive Bacteria/genetics , Humans , Inflammation/immunology , Inflammation/metabolism , Inflammation/microbiology , Mycobacterium/metabolism , Staphylococcal Infections/immunology , Staphylococcal Infections/metabolism , Staphylococcus aureus/metabolism , Streptococcus/metabolism , VaccinesABSTRACT
Numerous factors have, to date, been identified as playing a role in the regulation of Agr activity in Staphylococcus aureus, including transcription factors, antisense RNAs, and host elements. Herein we investigated the product of SAUSA300_1984 (termed MroQ), a transmembrane Abi-domain/M79 protease-family protein, as a novel effector of this system. Using a USA300 mroQ mutant, we observed a drastic reduction in proteolysis, hemolysis, and pigmentation that was fully complementable. This appears to result from diminished agr activity, as transcriptional analysis revealed significant decreases in expression of both RNAII and RNAIII in the mroQ mutant. Such effects appear to be direct, rather than indirect, as known agr effectors demonstrated limited alterations in their activity upon mroQ disruption. A comparison of RNA sequencing data sets for both mroQ and agr mutants revealed a profound overlap in their regulomes, with the majority of factors affected being known virulence determinants. Importantly, the preponderance of alterations in expression were more striking in the agr mutant, indicating that MroQ is necessary, but not sufficient, for Agr function. Mechanism profiling revealed that putative residues for metalloprotease activity within MroQ are required for its Agr-controlling effect; however, this was not wielded at the level of AgrD processing. Virulence assessment demonstrated that both mroQ and agr mutants exhibited increased formation of renal abscesses but decreased skin abscess formation alongside diminished dermonecrosis. Collectively, we present the characterization of a novel agr effector in S. aureus which would appear to be a direct regulator, potentially functioning via interaction with the AgrC histidine kinase.
Subject(s)
Bacterial Proteins/immunology , Gene Expression Regulation, Bacterial/immunology , Staphylococcal Infections/immunology , Staphylococcal Infections/pathology , Staphylococcus aureus/immunology , Transcription Factors/immunology , Virulence Factors/immunology , Animals , Bacterial Proteins/genetics , Female , Gene Expression Regulation, Bacterial/genetics , Humans , Mice , Models, Animal , Staphylococcal Infections/genetics , Staphylococcus aureus/genetics , Transcription Factors/genetics , Virulence Factors/geneticsABSTRACT
The Staphylococcus aureus cyclophilin PpiB is an intracellular peptidyl prolyl cis/trans isomerase (PPIase) that has previously been shown to contribute to secreted nuclease and hemolytic activity. In this study, we investigated the contribution of PpiB to S. aureus virulence. Using a murine abscess model of infection, we demonstrated that a ppiB mutant is attenuated for virulence. We went on to investigate the mechanism through which PpiB protein contributes to virulence, in particular the contribution of PpiB PPIase activity. We determined the amino acid residues that are important for PpiB PPIase activity and showed that a single amino acid substitution (F64A) completely abrogates PPIase activity. Using purified PpiB F64A protein in vitro, we showed that PPIase activity only partially contributes to Nuc refolding and that PpiB also possesses PPIase-independent activity. Using allelic exchange, we introduced the F64A substitution onto the S. aureus chromosome, generating a strain that produces enzymatically inactive PpiB. Analysis of the PpiB F64A strain revealed that PPIase activity is not required for hemolysis of human blood or virulence in a mouse. Together, these results demonstrate that PpiB contributes to S. aureus virulence via a mechanism unrelated to prolyl isomerase activity.
Subject(s)
Abscess/pathology , Bacterial Proteins/metabolism , Cyclophilins/metabolism , Staphylococcal Infections/pathology , Staphylococcus aureus/growth & development , Virulence Factors/metabolism , Abscess/microbiology , Amino Acid Substitution , Animals , Bacterial Proteins/genetics , Cyclophilins/genetics , DNA Mutational Analysis , Disease Models, Animal , Erythrocytes/microbiology , Gene Deletion , Hemolysis , Humans , Mice , Staphylococcal Infections/microbiology , Staphylococcus aureus/pathogenicity , Virulence , Virulence Factors/geneticsABSTRACT
Nitric oxide (NO) is generated from arginine and oxygen via NO synthase (NOS). Staphylococcus aureus NOS (saNOS) has previously been shown to affect virulence and resistance to exogenous oxidative stress, yet the exact mechanism is unknown. Herein, a previously undescribed role of saNOS in S. aureus aerobic physiology was reported. Specifically, aerobic S. aureus nos mutant cultures presented with elevated endogenous reactive oxygen species (ROS) and superoxide levels, as well as increased membrane potential, increased respiratory dehydrogenase activity and slightly elevated oxygen consumption. Elevated ROS levels in the nos mutant likely resulted from altered respiratory function, as inhibition of NADH dehydrogenase brought ROS levels back to wild-type levels. These results indicate that, in addition to its recently reported role in regulating the switch to nitrate-based respiration during low-oxygen growth, saNOS also plays a modulatory role during aerobic respiration. Multiple transcriptional changes were also observed in the nos mutant, including elevated expression of genes associated with oxidative/nitrosative stress, anaerobic respiration and lactate metabolism. Targeted metabolomics revealed decreased cellular lactate levels, and altered levels of TCA cycle intermediates, the latter of which may be related to decreased aconitase activity. Collectively, these findings demonstrate a key contribution of saNOS to S. aureus aerobic respiratory metabolism.
Subject(s)
Nitric Oxide Synthase/metabolism , Staphylococcus aureus/metabolism , Arginine/metabolism , Cell Physiological Phenomena/physiology , Nitrates/metabolism , Nitric Oxide/metabolism , Oxidation-Reduction , Oxidative Stress , Oxygen/metabolism , Oxygen Consumption/physiology , Reactive Oxygen Species/metabolism , Staphylococcal Infections/metabolism , Staphylococcus aureus/genetics , Superoxides/metabolism , VirulenceABSTRACT
Staphylococcus aureus is an important human pathogen that relies on a large repertoire of secreted and cell wall-associated proteins for pathogenesis. Consequently, the ability of the organism to cause disease is absolutely dependent on its ability to synthesize and successfully secrete these proteins. In this study, we investigate the role of peptidyl-prolyl cis/trans isomerases (PPIases) on the activity of the S. aureus secreted virulence factor nuclease (Nuc). We identify a staphylococcal cyclophilin-type PPIase (PpiB) that is required for optimal activity of Nuc. Disruption of ppiB results in decreased nuclease activity in culture supernatants; however, the levels of Nuc protein are not altered, suggesting that the decrease in activity results from misfolding of Nuc in the absence of PpiB. We go on to demonstrate that PpiB exhibits PPIase activity in vitro, is localized to the bacterial cytosol, and directly interacts with Nuc in vitro to accelerate the rate of Nuc refolding. Finally, we demonstrate an additional role for PpiB in S. aureus hemolysis and demonstrate that the S. aureus parvulin-type PPIase PrsA also plays a role in the activity of secreted virulence factors. The deletion of prsA leads to a decrease in secreted protease and phospholipase activity, similar to that observed in other Gram-positive pathogens. Together, these results demonstrate, for the first time to our knowledge, that PPIases play an important role in the secretion of virulence factors in S. aureus IMPORTANCE: Staphylococcus aureus is a highly dangerous bacterial pathogen capable of causing a variety of infections throughout the human body. The ability of S. aureus to cause disease is largely due to an extensive repertoire of secreted and cell wall-associated proteins, including adhesins, toxins, exoenzymes, and superantigens. These virulence factors, once produced, are typically transported across the cell membrane by the secretory (Sec) system in a denatured state. Consequently, once outside the cell, they must refold into their active form. This step often requires the assistance of bacterial folding proteins, such as PPIases. In this work, we investigate the role of PPIases in S. aureus and uncover a cyclophilin-type enzyme that assists in the folding/refolding of staphylococcal nuclease.
Subject(s)
Bacterial Proteins/metabolism , Gene Expression Regulation, Bacterial/physiology , Peptidylprolyl Isomerase/metabolism , Protein Folding , Staphylococcus aureus/enzymology , Virulence Factors , Bacterial Proteins/genetics , Gene Expression Regulation, Enzymologic/physiology , Mutation , Peptidylprolyl Isomerase/genetics , Staphylococcus aureus/genetics , Staphylococcus aureus/metabolismABSTRACT
Staphylococcus aureus SufT is composed solely of the domain of unknown function 59 (DUF59) and has a role in the maturation of iron-sulphur (Fe-S) proteins. We report that SufT is essential for S. aureus when growth is heavily reliant upon lipoamide-utilizing enzymes, but dispensable when this reliance is decreased. LipA requires Fe-S clusters for lipoic acid (LA) synthesis and a ΔsufT strain had phenotypes suggestive of decreased LA production and decreased activities of lipoamide-requiring enzymes. Fermentative growth, a null clpC allele, or decreased flux through the TCA cycle diminished the demand for LA and rendered SufT non-essential. Abundance of the Fe-S cluster carrier Nfu was increased in a ΔclpC strain and a null clpC allele was unable to suppress the LA requirement of a ΔsufT Δnfu strain. Over-expression of nfu suppressed the LA requirement of the ΔsufT strain. We propose a model wherein SufT, and by extension the DUF59, is essential for the maturation of holo-LipA in S. aureus cells experiencing a high demand for lipoamide-dependent enzymes. The findings presented suggest that the demand for products of Fe-S enzymes is a factor governing the usage of one Fe-S cluster assembly factor over another in the maturation of apo-proteins.
Subject(s)
Iron-Sulfur Proteins/metabolism , Staphylococcus aureus/metabolism , Aconitate Hydratase/metabolism , Bacterial Proteins/metabolism , Citric Acid Cycle , Escherichia coli Proteins , Iron/metabolism , Iron-Sulfur Proteins/genetics , Staphylococcal Infections , Staphylococcus aureus/genetics , Sulfur/metabolism , Thioctic Acid/analogs & derivatives , Thioctic Acid/genetics , Thioctic Acid/metabolism , Transcription FactorsABSTRACT
UNLABELLED: Global regulator of virulence A (GrvA) is a ToxR-family transcriptional regulator that activates locus of enterocyte effacement (LEE)-dependent adherence in enterohemorrhagic Escherichia coli (EHEC). LEE activation by GrvA requires the Rcs phosphorelay response regulator RcsB and is sensitive to physiologically relevant concentrations of bicarbonate, a known stimulant of virulence systems in intestinal pathogens. This study determines the genomic scale of GrvA-dependent regulation and uncovers details of the molecular mechanism underlying GrvA-dependent regulation of pathogenic mechanisms in EHEC. In a grvA-null background of EHEC strain TW14359, RNA sequencing analysis revealed the altered expression of over 700 genes, including the downregulation of LEE- and non-LEE-encoded effectors and the upregulation of genes for glutamate-dependent acid resistance (GDAR). Upregulation of GDAR genes corresponded with a marked increase in acid resistance. GrvA-dependent regulation of GDAR and the LEE required gadE, the central activator of GDAR genes and a direct repressor of the LEE. Control of gadE by GrvA was further determined to occur through downregulation of the gadE activator GadW. This interaction of GrvA with GadW-GadE represses the acid resistance phenotype, while it concomitantly activates the LEE-dependent adherence and secretion of immune subversion effectors. The results of this study significantly broaden the scope of GrvA-dependent regulation and its role in EHEC pathogenesis. IMPORTANCE: Enterohemorrhagic Escherichia coli (EHEC) is an intestinal human pathogen causing acute hemorrhagic colitis and life-threatening hemolytic-uremic syndrome. For successful transmission and gut colonization, EHEC relies on the glutamate-dependent acid resistance (GDAR) system and a type III secretion apparatus, encoded on the LEE pathogenicity island. This study investigates the mechanism whereby the DNA-binding regulator GrvA coordinates activation of the LEE with repression of GDAR. Investigating how these systems are regulated leads to an understanding of pathogenic behavior and novel strategies aimed at disease prevention and control.
Subject(s)
Enterohemorrhagic Escherichia coli/metabolism , Enterohemorrhagic Escherichia coli/pathogenicity , Escherichia coli Proteins/metabolism , Gene Expression Regulation, Bacterial/physiology , Transcription Factors/metabolism , Bacterial Adhesion/physiology , Enterohemorrhagic Escherichia coli/genetics , Escherichia coli Proteins/genetics , Glutamic Acid/metabolism , HT29 Cells , Humans , Hydrogen-Ion Concentration , Transcription Factors/genetics , VirulenceABSTRACT
Prenylation is the addition of prenyl groups to peptide chains or metabolites via the condensation of geranyl- or isopentenyl-diphosphate moieties by geranyltranstransferases. Although this process is extensively studied in eukaryotes, little is known about the influence of prenylation in prokaryotic species. To explore the role of this modification in bacteria, we generated a mutation in the geranyltranstransferase (IspA) of Staphylococcus aureus. Quite strikingly, the ispA mutant completely lacked pigment and exhibited a previously undescribed small colony variant-like phenotype. Further pleiotropic defects in cellular behavior were noted, including impaired growth, decreased ATP production, increased sensitivity to oxidative stress, increased resistance to aminoglycosides and cationic antimicrobial peptides, and decreased resistance to cell wall-targeting antibiotics. These latter effects appear to result from differences in envelope composition as ispA mutants have highly diffuse cell walls (particularly at the septum), marked alterations in fatty acid composition and increased membrane fluidity. Taken together, these data present an important characterization of prokaryotic prenylation and demonstrate that this process is central to a wealth of pathways involved in mediating cellular homeostasis in S. aureus.
Subject(s)
Cell Wall/metabolism , Geranyltranstransferase/genetics , Protein Prenylation , Staphylococcus aureus/genetics , Staphylococcus aureus/metabolism , Antimicrobial Cationic Peptides/pharmacology , Drug Resistance, Bacterial , Fatty Acids/analysis , Gene Expression Profiling , Geranyltranstransferase/metabolism , Membrane Fluidity , Microbial Sensitivity Tests , Mutation , Phenotype , Staphylococcus aureus/growth & developmentABSTRACT
Antibiotic spacer designs have proven effective at eradicating infection during a two-stage revision arthroplasty. Temporary reuse of the steam-sterilized femoral component and a new all poly tibia component has been described as an effective articulating antibiotic spacer, but sterility concerns persist. Six explanted cobalt chrome femurs from patients with grossly infected TKA's and six stock femurs inoculated with different bacterial species were confirmed to be bacteria-free after autoclaving under a standard gravity-displacement cycle. The effect of steam sterilization on cobalt chrome fragments contaminated with MRSA biofilm was analyzed microscopically to quantify remaining biofilm. The autoclave significantly reduced the biofilm burden on the cobalt chrome fragments. This study confirmed sterility of the femur after a standard gravity-displacement cycle (132°C, 27 PSIG, 10 minutes).
Subject(s)
Anti-Bacterial Agents/therapeutic use , Arthroplasty, Replacement, Knee/instrumentation , Knee Prosthesis/microbiology , Prosthesis-Related Infections/surgery , Reoperation/instrumentation , Acinetobacter baumannii , Aged , Aged, 80 and over , Biofilms , Cobalt/chemistry , Enterococcus faecium , Female , Femur/surgery , Humans , Klebsiella pneumoniae , Knee Joint/surgery , Male , Microscopy, Electron, Scanning , Middle Aged , Pilot Projects , Prosthesis Design , Prosthesis-Related Infections/prevention & control , Pseudomonas aeruginosa , Staphylococcus aureus , Staphylococcus epidermidis , Sterilization , Tibia/surgeryABSTRACT
In Gram-positive bacteria, and particularly the Firmicutes, the DNA-dependent RNA polymerase (RNAP) complex contains an additional subunit, termed the δ factor, or RpoE. This enigmatic protein has been studied for more than 30 years for various organisms, but its function is still not well understood. In this study, we investigated its role in the major human pathogen Staphylococcus aureus. We showed conservation of important structural regions of RpoE in S. aureus and other species and demonstrated binding to core RNAP that is mediated by the ß and/or ß' subunits. To identify the impact of the δ subunit on transcription, we performed transcriptome sequencing (RNA-seq) analysis and observed 191 differentially expressed genes in the rpoE mutant. Ontological analysis revealed, quite strikingly, that many of the downregulated genes were known virulence factors, while several mobile genetic elements (SaPI5 and prophage SA3usa) were strongly upregulated. Phenotypically, the rpoE mutant had decreased accumulation and/or activity of a number of key virulence factors, including alpha toxin, secreted proteases, and Panton-Valentine leukocidin (PVL). We further observed significantly decreased survival of the mutant in whole human blood, increased phagocytosis by human leukocytes, and impaired virulence in a murine model of infection. Collectively, our results demonstrate that the δ subunit of RNAP is a critical component of the S. aureus transcription machinery and plays an important role during infection.
Subject(s)
DNA-Directed DNA Polymerase/physiology , Promoter Regions, Genetic/physiology , Protein Subunits/physiology , Sigma Factor/physiology , Staphylococcus aureus/pathogenicity , Transcription Factors/physiology , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Gene Expression Regulation, Bacterial , Humans , Phagocytosis , Sigma Factor/genetics , Staphylococcal Infections/genetics , Staphylococcal Infections/microbiology , Staphylococcus aureus/genetics , Staphylococcus aureus/metabolism , Transcription Factors/genetics , Virulence/genetics , Virulence Factors/genetics , Virulence Factors/metabolismABSTRACT
Staphylococcus aureus is a versatile pathogen of humans and a continued public health concern due to the rise and spread of multidrug-resistant strains. As part of an ongoing investigation into the pathogenic mechanisms of this organism we previously demonstrated that an intracellular N-terminal processing protease is required for S. aureus virulence. Following on from this, here we examine the role of CtpA, the lone C-terminal processing protease of S. aureus. CtpA, a member of the S41 family, is a serine protease whose homologues in Gram-negative bacteria have been implicated in a range of biological functions, including pathogenesis. We demonstrate that S. aureus CtpA is localized to the bacterial cell wall and expression of the ctpA gene is maximal upon exposure to conditions encountered during infection. Disruption of the ctpA gene leads to decreased heat tolerance and increased sensitivity when exposed to components of the host immune system. Finally we demonstrate that the ctpA(-) mutant strain is attenuated for virulence in a murine model of infection. Our results represent the first characterization of a C-terminal processing protease in a pathogenic Gram-positive bacterium and show that it plays a critical role during infection.
Subject(s)
Bacterial Proteins/metabolism , Cell Wall/enzymology , Endopeptidases/metabolism , Staphylococcal Infections/microbiology , Staphylococcus aureus/enzymology , Staphylococcus aureus/pathogenicity , Amino Acid Sequence , Animals , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Cell Wall/genetics , Endopeptidases/chemistry , Endopeptidases/genetics , Gene Expression Regulation, Bacterial , Humans , Mice , Molecular Sequence Data , Multigene Family , Protein Transport , Sequence Alignment , Staphylococcus aureus/chemistry , Staphylococcus aureus/genetics , VirulenceABSTRACT
BACKGROUND: We previously identified an ECF sigma factor, σS, that is important in the stress and virulence response of Staphylococcus aureus. Transcriptional profiling of sigS revealed that it is differentially expressed in many laboratory and clinical isolates, suggesting the existence of regulatory networks that modulates its expression. RESULTS: To identify regulators of sigS, we performed a pull down assay using S. aureus lysates and the sigS promoter. Through this we identified CymR as a negative effector of sigS expression. Electrophoretic mobility shift assays (EMSAs) revealed that CymR directly binds to the sigS promoter and negatively effects transcription. To more globally explore genetic regulation of sigS, a Tn551 transposon screen was performed, and identified insertions in genes that are involved in amino acid biosynthesis, DNA replication, recombination and repair pathways, and transcriptional regulators. In efforts to identify gain of function mutations, methyl nitro-nitrosoguanidine mutagenesis was performed on a sigS-lacZ reporter fusion strain. From this a number of clones displaying sigS upregulation were subject to whole genome sequencing, leading to the identification of the lactose phosphotransferase repressor, lacR, and the membrane histidine kinase, kdpD, as central regulators of sigS expression. Again using EMSAs we determined that LacR is an indirect regulator of sigS expression, while the response regulator, KdpE, directly binds to the promoter region of sigS. CONCLUSIONS: Collectively, our work suggests a complex regulatory network exists in S. aureus that modulates expression of the ECF sigma factor, σS.
Subject(s)
Bacterial Proteins/genetics , Gene Expression Regulation, Bacterial/genetics , Sigma Factor/genetics , Staphylococcus aureus/genetics , DNA, Bacterial/genetics , Gene Expression Profiling/methods , Mutation/genetics , Promoter Regions, Genetic/genetics , Transcription, Genetic/genetics , Virulence/geneticsABSTRACT
Investigations into the biological role and composition of bacterial extracellular vesicles have grown in popularity in recent years. Vesicles perform a variety of functions during interactions with eukaryotic host cells, ranging from antibiotic resistance to immune modulation. It is necessary to isolate vesicles in order to understand their biological functions. Here we describe a polymer-based precipitation method allowing high-yield isolation of extracellular vesicles and their cargo RNA from the Gram-positive bacterium Staphylococcus aureus.
Subject(s)
Extracellular Vesicles , Staphylococcal Infections , Humans , Membranes , Gram-Positive Bacteria , RNAABSTRACT
Staphylococcus aureus colonizes the nares of approximately 30% of humans, a risk factor for opportunistic infections. To gain insight into S. aureus virulence potential in the spaceflight environment, we analyzed RNA-Seq, cellular proteomics, and metabolomics data from the "Biological Research in Canisters-23" (BRIC-23) GeneLab spaceflight experiment, a mission designed to measure the response of S. aureus to growth in low earth orbit on the international space station. This experiment used Biological Research in Canisters-Petri Dish Fixation Units (BRIC-PDFUs) to grow asynchronous ground control and spaceflight cultures of S. aureus for 48 h. RNAIII, the effector of the Accessory Gene Regulator (Agr) quorum sensing system, was the most highly upregulated gene transcript in spaceflight relative to ground controls. The agr operon gene transcripts were also highly upregulated during spaceflight, followed by genes encoding phenol-soluble modulins and secreted proteases, which are positively regulated by Agr. Upregulated spaceflight genes/proteins also had functions related to urease activity, type VII-like Ess secretion, and copper transport. We also performed secretome analysis of BRIC-23 culture supernatants, which revealed that spaceflight samples had increased abundance of secreted virulence factors, including Agr-regulated proteases (SspA, SspB), staphylococcal nuclease (Nuc), and EsxA (secreted by the Ess system). These data also indicated that S. aureus metabolism is altered in spaceflight conditions relative to the ground controls. Collectively, these data suggest that S. aureus experiences increased quorum sensing and altered expression of virulence factors in response to the spaceflight environment that may impact its pathogenic potential.
ABSTRACT
Humans commonly carry pathogenic bacteria asymptomatically, but the molecular factors underlying microbial asymptomatic carriage are poorly understood. We previously reported that two epidemiologically unassociated serotype M3 group A Streptococcus (GAS) carrier strains had an identical 12-bp deletion in the promoter of the gene encoding Mga, a global positive gene regulator. Herein, we report on studies designed to test the hypothesis that the identified 12-bp deletion in the mga promoter alters GAS virulence, thereby potentially contributing to the asymptomatic carrier phenotype. Using allelic exchange, we introduced the variant promoter into a serotype M3 invasive strain and the wild-type promoter into an asymptomatic carrier strain. Compared to strains with the wild-type mga promoter, we discovered that strains containing the promoter with the 12-bp deletion produced significantly fewer mga and Mga-regulated gene transcripts. Consistent with decreased mga transcripts, strains containing the variant mga promoter were also significantly less virulent in in vivo and ex vivo models of GAS disease. Further, we provide evidence that the pleiotropic regulator protein CodY binds to the mga promoter and that the 12-bp deletion in the mga promoter reduces CodY-mediated mga transcription. We conclude that the naturally occurring 12-bp deletion in the mga promoter significantly alters the pathogen-host interaction of these asymptomatic carrier strains. Our findings provide new insight into the molecular basis of the carrier state of an important human pathogen.