Biomedical subjects

Cuong Vuong

Publications and source records attributed to Cuong Vuong.

14 recordsLinked to original sources

PubMed2006

Staphylococcus quorum sensing in biofilm formation and infection.

Cell population density-dependent regulation of gene expression is an important determinant of bacterial pathogenesis. Staphylococci have two quorum-sensing (QS) systems. The accessory gene regulator (agr) is genus specific and uses a post-translationally modified peptide as an autoinducing signal. In the pathogens Staphylococcus aureus and Staphylococcus epidermidis, agr controls the expression of a series of toxins and virulence factors and the interaction with the innate immune system. However, the role of agr during infection is controversial. A possible second QS system of staphylococci, luxS, is found in a variety of Gram-positive and Gram-negative bacteria. Importantly, unlike many QS systems described in Gram-negative bacteria, agr and luxS of staphylococci reduce rather than induce biofilm formation and virulence during biofilm-associated infection. agr enhances biofilm detachment by up-regulation of the expression of detergent-like peptides, whereas luxS reduces cell-to-cell adhesion by down-regulating expression of biofilm exopolysaccharide. Significant QS activity in staphylococci is observed for actively growing cells at a high cell density, such as during the initial stages of an infection and under optimal environmental conditions. In contrast, the metabolically quiescent biofilm mode of growth appears to be characterized by an overall low activity of the staphylococcal QS systems. It remains to be shown whether QS control in staphylococci represents a promising target for the development of novel antibacterial agents.

Animals↗

PubMed2006

Characterization of the Staphylococcus epidermidis accessory-gene regulator response: quorum-sensing regulation of resistance to human innate host defense.

Staphylococci are important opportunistic pathogens. However, there is a lack of information on how these bacteria survive inside the human body during infection. This study demonstrates that quorum-sensing regulation in Staphylococcus epidermidis protects it from key mechanisms of human innate host defense. To gain a better understanding of the basis of the observed phenotype, the agr quorum-sensing regulon of S. epidermidis was characterized by a genomewide analysis of gene expression. The gene-expression data indicate that agr adapts bacterial physiology to stationary growth and, furthermore, that it controls a series of virulence factors, including degradative exoenzymes possibly involved in resistance to antimicrobial peptides. Remarkably, agr also regulates general and oxidative stress-response factors, including detoxifying enzymes of reactive oxygen species. Taken together, the results of this study indicate that quorum-sensing regulation in staphylococci has important, previously unknown functions that contribute to protection from mechanisms of human innate host defense--and, therefore, to the pathogen's survival in the human host.

Bacterial Proteins↗

PubMed2006

Role of the luxS quorum-sensing system in biofilm formation and virulence of Staphylococcus epidermidis.

Nosocomial infections caused by Staphylococcus epidermidis are characterized by biofilm formation on implanted medical devices. Quorum-sensing regulation plays a major role in the biofilm development of many bacterial pathogens. Here, we describe luxS, a quorum-sensing system in staphylococci that has a significant impact on biofilm development and virulence. We constructed an isogenic DeltaluxS mutant strain of a biofilm-forming clinical isolate of S. epidermidis and demonstrated that luxS signaling is functional in S. epidermidis. The mutant strain showed increased biofilm formation in vitro and enhanced virulence in a rat model of biofilm-associated infection. Genetic complementation and addition of autoinducer 2-containing culture filtrate restored the wild-type phenotype, demonstrating that luxS repressed biofilm formation through a cell-cell signaling mechanism based on autoinducer 2 secretion. Enhanced production of the biofilm exopolysaccharide polysaccharide intercellular adhesin in the mutant strain is presumably the major cause of the observed phenotype. The agr quorum-sensing system has previously been shown to impact biofilm development and biofilm-associated infection in a way similar to that of luxS, although by regulation of different factors. Our study indicates a general scheme of quorum-sensing regulation of biofilm development in staphylococci, which contrasts with that observed in many other bacterial pathogens.

Animals↗

PubMed2005

Conversion of Staphylococcus epidermidis strains from commensal to invasive by expression of the ica locus encoding production of biofilm exopolysaccharide.

To test if biofilm formation in Staphylococcus epidermidis is dependent on the polysaccharide intercellular adhesin, whose biosynthesis is driven by the ica locus, a plasmid containing the ica locus was transferred to three ica-negative strains. Using in vitro biofilm assays and a rat central venous catheter infection model, we confirmed the importance of the ica locus for biofilm production and pathogenesis of S. epidermidis.

Animals↗

PubMed2005

Staphylococcus epidermidis polysaccharide intercellular adhesin production significantly increases during tricarboxylic acid cycle stress.

Staphylococcal polysaccharide intercellular adhesin (PIA) is important for the development of a mature biofilm. PIA production is increased during growth in a nutrient-replete or iron-limited medium and under conditions of low oxygen availability. Additionally, stress-inducing stimuli such as heat, ethanol, and high concentrations of salt increase the production of PIA. These same environmental conditions are known to repress tricarboxylic acid (TCA) cycle activity, leading us to hypothesize that altering TCA cycle activity would affect PIA production. Culturing Staphylococcus epidermidis with a low concentration of the TCA cycle inhibitor fluorocitrate dramatically increased PIA production without impairing glucose catabolism, the growth rate, or the growth yields. These data lead us to speculate that one mechanism by which staphylococci perceive external environmental change is through alterations in TCA cycle activity leading to changes in the intracellular levels of biosynthetic intermediates, ATP, or the redox status of the cell. These changes in the metabolic status of the bacteria result in the attenuation or augmentation of PIA production.

Acetic Acid↗

PubMed2005

Key role of poly-gamma-DL-glutamic acid in immune evasion and virulence of Staphylococcus epidermidis.

Coagulase-negative staphylococci, with the leading species Staphylococcus epidermidis, are the predominant cause of hospital-acquired infections. Treatment is especially difficult owing to biofilm formation and frequent antibiotic resistance. However, virulence mechanisms of these important opportunistic pathogens have remained poorly characterized. Here we demonstrate that S. epidermidis secretes poly-gamma-DL-glutamic acid (PGA) to facilitate growth and survival in the human host. Importantly, PGA efficiently sheltered S. epidermidis from key components of innate host defense, namely antimicrobial peptides and neutrophil phagocytosis, and was indispensable for persistence during device-related infection. Furthermore, PGA protected S. epidermidis from high salt concentration, a key feature of its natural environment, the human skin. Notably, PGA was synthesized by all tested strains of S. epidermidis and a series of closely related coagulase-negative staphylococci, most of which are opportunistic pathogens. Our study presents important novel biological functions for PGA and indicates that PGA represents an excellent target for therapeutic maneuvers aimed at treating disease caused by S. epidermidis and related staphylococci.

Animals↗

PubMed2004

A crucial role for exopolysaccharide modification in bacterial biofilm formation, immune evasion, and virulence.

Biofilms play an important role in many chronic bacterial infections. Production of an extracellular mixture of sugar polymers called exopolysaccharide is characteristic and critical for biofilm formation. However, there is limited information about the mechanisms involved in the biosynthesis and modification of exopolysaccharide components and how these processes influence bacterial pathogenesis. Staphylococcus epidermidis is an important human pathogen that frequently causes persistent infections by biofilm formation on indwelling medical devices. It produces a poly-N-acetylglucosamine molecule that emerges as an exopolysaccharide component of many bacterial pathogens. Using a novel method based on size exclusion chromatography-mass spectrometry, we demonstrate that the surface-attached protein IcaB is responsible for deacetylation of the poly-N-acetylglucosamine molecule. Most likely due to the loss of its cationic character, non-deacetylated poly-acetylglucosamine in an isogenic icaB mutant strain was devoid of the ability to attach to the bacterial cell surface. Importantly, deacetylation of the polymer was essential for key virulence mechanisms of S. epidermidis, namely biofilm formation, colonization, and resistance to neutrophil phagocytosis and human antibacterial peptides. Furthermore, persistence of the icaB mutant strain was significantly impaired in a murine model of device-related infection. This is the first study to describe a mechanism of exopolysaccharide modification that is indispensable for the development of biofilm-associated human disease. Notably, this general virulence mechanism is likely similar for other pathogenic bacteria and constitutes an excellent target for therapeutic maneuvers aimed at combating biofilm-associated infection.

Acetylation↗

PubMed2004

Increased colonization of indwelling medical devices by quorum-sensing mutants of Staphylococcus epidermidis in vivo.

Infections with the leading nosocomial pathogen Staphylococcus epidermidis are characterized by biofilm development on indwelling medical devices. We demonstrate that the quorum-sensing regulator agr affects the biofilm development of S. epidermidis in an unexpected fashion and is likely involved in promoting biofilm detachment. An isogenic agr mutant showed increased biofilm development and colonization in a rabbit model. In addition, nonfunctional agr occurred more frequently among strains isolated from infections of joint prostheses. Lack of functionality was based on mutations, including insertion of an IS256 element. Relative to other bacterial pathogens, quorum sensing in S. epidermidis thus has a different role during biofilm development and biofilm-associated infection. Our results indicate that disabling agr likely enhances the success of S. epidermidis during infection of indwelling medical devices. The permanent elimination of quorum-sensing regulation used by S. epidermidis represents a surprising and unusual means to adapt to a certain environment and type of infection.

Animals↗

PubMed2004

Engagement of the pathogen survival response used by group A Streptococcus to avert destruction by innate host defense.

Neutrophils are a critical component of human innate host defense and efficiently kill the vast majority of invading microorganisms. However, bacterial pathogens such as group A Streptococcus (GAS) successfully avert destruction by neutrophils to cause human infections. Relatively little is known about how pathogens detect components of the innate immune system to respond and survive within the host. In this study, we show that inactivation of a two-component gene regulatory system designated Ihk-Irr significantly attenuates streptococcal virulence in mouse models of soft tissue infection and bacteremia. Microarray analysis of wild-type and irr-negative mutant (irr mutant) GAS strains revealed that Ihk-Irr influenced expression of 20% of all transcripts in the pathogen genome. Notably, at least 11 genes involved in cell wall synthesis, turnover, and/or modification were down-regulated in the irr mutant strain. Compared with the wild-type strain, significantly more of the irr mutant strain was killed by human neutrophil components that destroy bacteria by targeting the cell envelope (cell wall and/or membrane). Unexpectedly, expression of ihk and irr was dramatically increased in the wild-type strain exposed to these same neutrophil products under conditions that favored cell envelope damage. We report a GAS mechanism for detection of innate host defense that initiates the pathogen survival response, in which cell wall synthesis is critical. Importantly, our studies identify specific genes in the pathogen survival response as potential targets to control human infections.

Animals↗

PubMed2004

Polysaccharide intercellular adhesin (PIA) protects Staphylococcus epidermidis against major components of the human innate immune system.

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is the leading cause of nosocomial and biofilm-associated infections. Little is known about the mechanisms by which S. epidermidis protects itself against the innate human immune system during colonization and infection. We used scanning electron microscopy to demonstrate that the exopolysaccharide intercellular adhesin (PIA) resides in fibrous strands on the bacterial cell surface, and that lack of PIA production results in complete loss of the extracellular matrix material that has been suggested to mediate immune evasion. Phagocytosis and killing by human polymorphonuclear leucocytes was significantly increased in a mutant strain lacking PIA production compared with the wild-type strain. The mutant strain was also significantly more susceptible to killing by major antibacterial peptides of human skin, cationic human beta-defensin 3 and LL-37, and anionic dermcidin. PIA represents the first defined factor of the staphylococcal biofilm matrix that protects against major components of human innate host defence.

Humans↗

PubMed2004

Regulated expression of pathogen-associated molecular pattern molecules in Staphylococcus epidermidis: quorum-sensing determines pro-inflammatory capacity and production of phenol-soluble modulins.

Phenol-soluble modulin (PSM) is a peptide complex produced by the nosocomial pathogen Staphylococcus epidermidis that has a strong capacity to activate the human innate immune response. We developed a novel method based on liquid chromatography-mass spectrometry (LC-MS) to quantify the production of the individual PSM components. Each PSM peptide was abundant in most of the 76 S epidermidis strains tested. Importantly, none of the PSM components were secreted by an agr mutant strain, indicating that PSM synthesis is regulated strictly by the agr quorum-sensing system. Furthermore, the agr mutant strain failed to elicit production of TNFalpha by human myeloid cells and induced significantly less neutrophil chemotaxis compared with the wild-type strain. Thus, quorum-sensing in S. epidermidis dramatically influenced activation of human host defence. We propose that an agr quorum-sensing mechanism facilitates growth and survival in infected hosts by adapting production of the pro-inflammatory PSMs to the stage of infection.

Bacterial Toxins↗

PubMed2003

Quorum-sensing control of biofilm factors in Staphylococcus epidermidis.

Staphylococcus epidermidis is the most frequent cause of nosocomial sepsis and catheter-related infections, in which biofilm formation is considered to be the main virulence mechanism. Quorum-sensing systems have been recognized as important regulators of virulence and biofilm formation in many bacteria. There is a single quorum-sensing system in S. epidermidis encoded by the agr operon. To investigate quorum-sensing control of biofilm formation, we constructed an agr deletion mutant, assayed for the different stages of biofilm formation, and determined agr-dependent regulation of biofilm factors. The agr mutant showed increased biofilm formation, primary attachment, and expression of the autolysin AtlE, but lacked delta-toxin production. However, the level of polysaccharide intercellular adhesin expression was equivalent to the isogenic wild-type strain. In contrast to AtlE, which is known to influence primary attachment, delta-toxin appeared to exert its effect on attachment to polystyrene during later stages of biofilm formation. Importantly, addition of cross-inhibiting pheromones mimicked an agr mutation and significantly enhanced biofilm formation, which suggests that care should be used when treating S. epidermidis infections with cross-inhibiting peptides. Our data demonstrate the importance of quorum sensing in the establishment of a biofilm in this critical human pathogen.

Bacterial Adhesion↗

PubMed2003

Control of antimicrobial peptide synthesis by the agr quorum sensing system in Staphylococcus epidermidis: activity of the lantibiotic epidermin is regulated at the level of precursor peptide processing.

The accessory gene regulator (agr) quorum sensing system in staphylococci is responsible for the regulation of surface proteins and exoproteins, including many virulence factors in the pathogenic species Staphylococcus aureus and S. epidermidis. Strain S. epidermidis Tü3298 produces the lantibiotic epidermin. An isogenic agr deletion mutant of this strain showed a strong reduction of epidermin production. Detailed analysis of the impact of agr on epidermin biosynthesis revealed that agr does not interfere with the transcription of epidermin biosynthetic genes, but controls the extracellular processing of the N-terminal leader peptide by the EpiP protease.

Amino Acid Sequence↗

PubMed2002

Staphylococcus epidermidis infections.

The opportunistic human pathogen Staphylococcus epidermidis has become the most important cause of nosocomial infections in recent years. Its pathogenicity is mainly due to the ability to form biofilms on indwelling medical devices. In a biofilm, S. epidermidis is protected against attacks from the immune system and against antibiotic treatment, making S. epidermidis infections difficult to eradicate.

Bacterial Adhesion↗