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Biomedical subjects

Michael Otto

Publications and source records attributed to Michael Otto.

At least 19 recordsLinked to original sources
PubMed2006

The human anionic antimicrobial peptide dermcidin induces proteolytic defence mechanisms in staphylococci.

Antimicrobial peptides (AMPs) represent a key component of innate host defence against bacterial pathogens. Bacterial resistance mechanisms usually depend on the characteristic positive charge of AMPs. However, several human cell types also produce anionic AMPs, mechanisms of resistance to which are poorly understood. Here we demonstrate that the skin commensal and leading nosocomial pathogen Staphylococcus epidermidis senses and efficiently inactivates the anionic AMP dermcidin. Dermcidin induced differential expression of global regulatory systems, leading to increased expression of proteases with the capacity to degrade dermcidin, particularly S. epidermidis SepA. A similar induction of extracellular proteolytic activity was found in Staphylococcus aureus, suggesting a common regulatory mechanism in staphylococci. Notably, human cationic AMPs also led to the activation of global regulators, but inactivation of dermcidin by SepA was much more effective than of the tested cationic peptides. The ability to react to the unusual, anionic dermcidin with effective countermeasures likely contributes to the extraordinary success of staphylococci as colonizers and infective agents on human epithelia. Our study indicates that staphylococci can react to human AMPs by specific mechanisms of resistance and establishes a crucial role for staphylococcal proteases in the interaction with human innate host defence.

Adaptation, Physiological↗
PubMed2006

Is Panton-Valentine leukocidin the major virulence determinant in community-associated methicillin-resistant Staphylococcus aureus disease?

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major problem in hospitals, and it is now spreading in the community. A single toxin, Panton-Valentine leukocidin (PVL), has been linked by epidemiological studies to community-associated MRSA (CA-MRSA) disease. However, the role that PVL plays in the pathogenesis of CA-MRSA has not been tested directly. To that end, we used mouse infection models to compare the virulence of PVL-positive with that of PVL-negative CA-MRSA representing the leading disease-causing strains. Unexpectedly, strains lacking PVL were as virulent in mouse sepsis and abscess models as those containing the leukotoxin. Isogenic PVL-negative (lukS/F-PV knockout) strains of USA300 and USA400 were as lethal as wild-type strains in a sepsis model, and they caused comparable skin disease. Moreover, lysis of human neutrophils and pathogen survival after phagocytosis were similar between wild-type and mutant strains. Although the toxin may be a highly linked epidemiological marker for CA-MRSA strains, we conclude that PVL is not the major virulence determinant of CA-MRSA.

Abscess↗
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

Combining pharmacotherapy with cognitive behavioral therapy: traditional and new approaches.

Given the ever-increasing sources of trauma both nationally and globally, it is imperative to develop new and better treatments for anxiety disorders such as posttraumatic stress disorder (PTSD). This review is a collection of presentations that seek to do just that, either by using pharmacotherapy to try to prevent or erase the formation of traumatic fear memories, or to enhance exposure-based cognitive-behavioral therapy using pharmacological agents that have been effective in enhanced extinction of fear in rodents.

Cognitive Behavioral Therapy↗
PubMed2006

Neutrophil chemotaxis by pathogen-associated molecular patterns--formylated peptides are crucial but not the sole neutrophil attractants produced by Staphylococcus aureus.

The chemotactic migration of phagocytes to sites of infection, guided by gradients of microbial molecules, plays a key role in the first line of host defence. Bacteria are distinguished from eukaryotes by initiation of protein synthesis with formyl methionine. Synthetic formylated peptides (FPs) have been shown to be chemotactic for phagocytes, leading to the concept of FPs as pathogen-associated molecular patterns (PAMPs). However, it remains unclear whether FPs are major chemoattractants released by bacteria and whether further chemoattractants are produced. A Staphylococcus aureus mutant whose formyltransferase gene was inactivated (Deltafmt) produced no FPs and the in vitro and in vivo ability of Deltafmt culture supernatants to recruit neutrophils was considerably reduced compared with those of the parental strain. However, some chemotactic activity was retained, indicating that bacteria produce also unknown, non-FP chemoattractants. The activity of these novel PAMPs was sensitive to pertussis toxin but insensitive to the formyl peptide receptor inhibitor CHIPS. Deltafmt culture supernatants caused reduced calcium ion fluxes and reduced CD11b upregulation in neutrophils compared with wild-type supernatants. These data demonstrate an important role of FPs in innate immunity against bacterial infections and indicate that host chemotaxis receptors recognize a larger set of bacterial molecules than previously thought.

Animals↗
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

Factors characterizing Staphylococcus epidermidis invasiveness determined by comparative genomics.

Virulence mechanisms of the leading nosocomial pathogen Staphylococcus epidermidis are poorly understood. We used microarray-based genome-wide comparison of clinical and commensal S. epidermidis strains to identify putative virulence determinants. Our study revealed high genetic variability of the S. epidermidis genome, new markers for invasiveness of S. epidermidis, and potential targets for drug development against S. epidermidis infections.

Bacterial Proteins↗
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

Quorum-sensing control in Staphylococci -- a target for antimicrobial drug therapy?

Today, we find ourselves in an urgent need for novel antibacterial drugs, as many important human pathogens have acquired multiple antibiotic resistance factors. Among those, Staphylococcus aureus and S. epidermidis play a major role as the leading sources of nosocomial infections. Recently, it has been suggested to develop therapeutics that attack bacterial virulence rather than kill bacteria. Such drugs are called "antipathogenic" and are believed to reduce the development of antibiotic resistance. Specifically, cell-density-dependent gene regulation (quorum-sensing) in bacteria has been proposed as a potential target. While promising reports exist about quorum-sensing blockers in gram-negative bacteria, the use of the staphylococcal quorum-sensing system as a drug target is now seen in an increasingly critical way. Inhibition of quorum-sensing in Staphylococcus has been shown to enhance biofilm formation. Furthermore, down-regulation or mutation of the Staphylococcus quorum-sensing system increases bacterial persistence in device-related infection, suggesting that interference with quorum-sensing would enhance rather than suppress this important type of staphylococcal disease. The chemical nature and biological function of another proposed staphylococcal quorum-sensing inhibitor, named "RIP", are insufficiently characterized. Targeting quorum-sensing systems might in principle constitute a reasonable way to find novel antibacterial drugs. However, as outlined here, this approach requires careful investigation in every specific pathogen and type of infection.

Anti-Bacterial Agents↗
PubMed2004

Genomewide analysis of gene expression in Staphylococcus epidermidis biofilms: insights into the pathophysiology of S. epidermidis biofilms and the role of phenol-soluble modulins in formation of biofilms.

Many bacterial pathogens form cellular agglomerations known as biofilms, which considerably limit the success of both antibiotic treatment and the human immune defense. To gain insight into the pathophysiology of the leading nosocomial pathogen, Staphylococcus epidermidis, we analyzed the genome of biofilm-forming S. epidermidis, constructed a microarray representing its entire transcriptome, and performed expression profiling of an S. epidermidis biofilm. Gene-regulated processes in the biofilm led to a nonaggressive and protected form of bacterial growth with low metabolic activity, which is optimally suited to guarantee long-term survival during chronic infection. A class of peptides known as phenol-soluble modulins, which combine proinflammatory activity with a putative role in detachment of biofilms, evolved as potential key determinants controlling the switch between aggressive and quiescent modes of infection. Our data suggest that S. epidermidis adjusts its lifestyle to varying requirements during colonization and infection by means of an expansive change of gene expression. The observed physiological characteristics of the biofilm mode of growth--in particular, the contribution of surfactant-like peptides--might serve as a model for a variety of biofilm-forming pathogens.

Bacterial Toxins↗
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

Inactivation of a bacterial virulence pheromone by phagocyte-derived oxidants: new role for the NADPH oxidase in host defense.

Quorum sensing triggers virulence factor expression in medically important bacterial pathogens in response to a density-dependent increase in one or more autoinducing pheromones. Here, we show that phagocyte-derived oxidants target these autoinducers for inactivation as an innate defense mechanism of the host. In a skin infection model, expression of phagocyte NADPH oxidase, myeloperoxidase, or inducible nitric oxide synthase was critical for defense against a quorum-sensing pathogen, Staphylococcus aureus, but not for defense against a quorum sensing-deficient mutant. A virulence-inducing peptide of S. aureus was inactivated in vitro and in vivo by reactive oxygen and nitrogen intermediates, including HOCl and ONOO(-). Inactivation of the autoinducer prevented both the up-regulation of virulence gene expression and the downstream sequelae. MS analysis of the inactivated peptide demonstrated that oxidation of the C-terminal methionine was primarily responsible for loss of activity. Treatment of WT but not NADPH oxidase-deficient mice with N-acetyl methionine to scavenge the inhibitory oxidants increased in vivo quorum sensing independently of the bacterial burden at the site of infection. Thus, oxidant-mediated inactivation of an autoinducing peptide from S. aureus is a critical innate defense mechanism against infection with this pathogen.

Animals↗
PubMed2004

Activity of Staphylococcus epidermidis phenol-soluble modulin peptides expressed in Staphylococcus carnosus.

Staphylococcus epidermidis releases a group of peptides termed phenol-soluble modulin (PSM) that stimulate macrophages. The structure of 3 peptides (PSM alpha, PSM beta, and PSM gamma ) have been described. We report a fourth peptide (PSM delta ), which is a 23mer with the structure fMSIVSTIIEVVKTIVDIVKKFKK. The gene for each of the 4 peptides was introduced singly into Staphylococcus carnosus, and the PSM-like activity of culture medium and bacterial extract were significantly greater than those of the parent strain. PSM peptides from each of the S. carnosus-expressing strains were purified and analyzed by liquid chromatography-mass spectrometry. The products, which appeared to form aggregates, were active in the activation of human immunodeficiency virus type 1 long-terminal repeat and the production of tumor necrosis factor- alpha by the macrophage cell line THP-1. These findings suggest that PSM peptides are responsible, in part, for the modulin-like activity of staphylococci and may contribute to the development of severe staphylococcal sepsis.

Amino Acid Sequence↗