Staphylococcal lipases: molecular characterisation, secretion, and processing

Secretory proteins in the orchestration of microbial virulence: The curious case of Staphylococcus aureus

Microbial virulence showcases an excellent model for adaptive changes that enable an organism to survive and proliferate in a hostile environment and exploit host resources to its own benefit. In Staphylococcus aureus, an opportunistic pathogen of the human host, known for the diversity of the disease conditions it inflicts and the rapid evolution of antibiotic resistance, virulence is a consequence of having a highly plastic genome that is amenable to quick reprogramming and the ability to express a diverse arsenal of virulence factors. Virulence factors that are secreted to the host milieu effectively manipulate the host conditions to favor bacterial survival and growth. They assist in colonization, nutrient acquisition, immune evasion, and systemic spread. The structural and functional characteristics of the secreted virulence proteins have been shaped to assist S. aureus in thriving and disseminating effectively within the host environment and exploiting the host resources to its best benefit. With the aim of highlighting the importance of secreted virulence proteins in bacterial virulence, the present chapter provides a comprehensive account of the role of the major secreted proteins of S. aureus in orchestrating its virulence in the human host.

Branched chain fatty acid synthesis drives tissue-specific innate immune response and infection dynamics of Staphylococcus aureus

Fatty acid-derived acyl chains of phospholipids and lipoproteins are central to bacterial membrane fluidity and lipoprotein function. Though it can incorporate exogenous unsaturated fatty acids (UFA), Staphylococcus aureus synthesizes branched chain fatty acids (BCFA), not UFA, to modulate or increase membrane fluidity. However, both endogenous BCFA and exogenous UFA can be attached to bacterial lipoproteins. Furthermore, S. aureus membrane lipid content varies based upon the amount of exogenous lipid in the environment. Thus far, the relevance of acyl chain diversity within the S. aureus cell envelope is limited to the observation that attachment of UFA to lipoproteins enhances cytokine secretion by cell lines in a TLR2-dependent manner. Here, we leveraged a BCFA auxotroph of S. aureus and determined that driving UFA incorporation disrupted infection dynamics and increased cytokine production in the liver during systemic infection of mice. In contrast, infection of TLR2-deficient mice restored inflammatory cytokines and bacterial burden to wildtype levels, linking the shift in acyl chain composition toward UFA to detrimental immune activation in vivo. In in vitro studies, bacterial lipoproteins isolated from UFA-supplemented cultures were resistant to lipase-mediated ester hydrolysis and exhibited heightened TLR2-dependent innate cell activation, whereas lipoproteins with BCFA esters were completely inactivated after lipase treatment. These results suggest that de novo synthesis of BCFA reduces lipoprotein-mediated TLR2 activation and improves lipase-mediated hydrolysis making it an important determinant of innate immunity. Overall, this study highlights the potential relevance of cell envelope acyl chain repertoire in infection dynamics of bacterial pathogens.

Staphylococcus aureus secreted lipases do not inhibit innate immune killing mechanisms

Background:Staphylococcus aureus causes an array of diseases in both humans and livestock. Pathogenesis is mediated by a plethora of proteins secreted by S. aureus, many of which remain incompletely characterised. For example, S. aureus abundantly secretes two isoforms of the enzyme lipase into the extracellular milieu, where they scavenge upon polymeric triglycerides. It has previously been suggested that lipases may interfere with the function of innate immune cells, such as macrophages and neutrophils, but the impact of lipases on phagocytic killing mechanisms remains unknown.

Methods: We employed the epidemic S. aureus clone USA300 strain LAC and its lipase deficient isogenic mutant, along with recombinant lipase proteins, in in vitro experimental infection assays. To determine if lipases can inhibit innate immune killing mechanisms, the bactericidal activity of whole blood, human neutrophils, and macrophages was analysed. In addition, gentamycin protection assays were carried out to examine the influence of lipases on S. aureus innate immune cell escape.

Results: There were no differences in the survival of S. aureus USA300 LAC wild type and its lipase-deficient isogenic mutant after incubation with human whole blood or neutrophils. Furthermore, there was no detectable lipase-dependent effect on phagocytosis, intracellular survival, or escape from both human primary and immortalised cell line macrophages, even upon supplementation with exogenous recombinant lipases.

Conclusions: S. aureus lipases do not inhibit bacterial killing mechanisms of human macrophages, neutrophils, or whole blood. These findings broaden our understanding of the interaction of S. aureus with the innate immune system.

Living in Your Skin: Microbes, Molecules, and Mechanisms

Human skin functions as a physical, chemical, and immune barrier against the external environment while also providing a protective niche for its resident microbiota, known as the skin microbiome. Cooperation between the microbiota, host skin cells, and the immune system is responsible for maintenance of skin health, and a disruption to this delicate balance, such as by pathogen invasion or a breach in the skin barrier, may lead to impaired skin function.

Human skin functions as a physical, chemical, and immune barrier against the external environment while also providing a protective niche for its resident microbiota, known as the skin microbiome. Cooperation between the microbiota, host skin cells, and the immune system is responsible for maintenance of skin health, and a disruption to this delicate balance, such as by pathogen invasion or a breach in the skin barrier, may lead to impaired skin function. In this minireview, we describe the role of the microbiome in microbe, host, and immune interactions under distinct skin states, including homeostasis, tissue repair, and wound infection. Furthermore, we highlight the growing number of diverse microbial metabolites and products that have been identified to mediate these interactions, particularly those involved in host-microbe communication and defensive symbiosis. We also address the contextual pathogenicity exhibited by many skin commensals and provide insight into future directions in the skin microbiome field.

Staphylococcus aureus secreted lipases do not inhibit innate immune killing mechanisms

Background: Staphylococcus aureus causes an array of diseases in both humans and livestock. Pathogenesis is mediated by a plethora of proteins secreted by S. aureus, many of which remain incompletely characterised. For example, S. aureus abundantly secretes two isoforms of the enzyme lipase into the extracellular milieu, where they scavenge upon polymeric triglycerides. It has previously been suggested that lipases may interfere with the function of innate immune cells, such as macrophages and neutrophils, but the impact of lipases on phagocytic killing mechanisms remains unknown. Methods: We employed the epidemic S. aureus clone USA300 strain LAC and its lipase deficient isogenic mutant, along with recombinant lipase proteins, in in vitro experimental infection assays. To determine if lipases can inhibit innate immune killing mechanisms, the bactericidal activity of whole blood, human neutrophils, and macrophages was analysed. In addition, gentamycin protection assays were carried out to examine the influence of lipases on S. aureus innate immune cell escape. Results: There were no differences in the survival of S. aureus USA300 LAC wild type and its lipase-deficient isogenic mutant after incubation with human whole blood or neutrophils. Furthermore, there was no detectable lipase-dependent effect on phagocytosis, intracellular survival, or escape from both human primary and immortalised cell line macrophages, even upon supplementation with exogenous recombinant lipases. Conclusions: S. aureus lipases do not inhibit bacterial killing mechanisms of human macrophages, neutrophils, or whole blood. These findings broaden our understanding of the interaction of S. aureus with the innate immune system.

Seasonal variations in the skin parameters of Caucasian women from Central Europe

BACKGROUND

The human skin is greatly affected by external factors such as UV radiation (UVR), ambient temperature (T), and air humidity. These factors oscillate during the year giving rise to the seasonal variations in the skin properties. The aim of this study was to evaluate the effect of seasons, environmental T, relative and absolute humidity on the skin parameters of Caucasian women, perform a literature review and discuss the possible factors lying behind the found changes.

MATERIALS AND METHODS

We measured stratum corneum (SC) hydration, transepidermal water loss (TEWL), sebum level, erythema index, and elasticity parameters R2 and R7 on the forehead and the cheek of Caucasian women from the Czech Republic throughout the year. We also performed a non-systematic literature review focused on the seasonal variations in these skin parameters.

RESULTS

We confirmed a well-documented low SC hydration and sebum production in winter. In spring, we found the lowest TEWL (on the forehead) and the highest SC hydration but also the highest erythema index and the lowest elasticity presumably indicating skin photodamage. For most of the skin parameters, the seasonal variations probably arise due to a complex action of different factors as we extensively discussed.

CONCLUSION

The data about the seasonal variations in the skin parameters are still highly inconsistent and further studies are needed for better understanding of the normal skin changes throughout the year.

Staphylococcus aureus Lipase 1 Enhances Influenza A Virus Replication

Influenza A virus (IAV) causes annual epidemics and sporadic pandemics of respiratory disease. Secondary bacterial coinfection by organisms such as Staphylococcus aureus is the most common complication of primary IAV infection and is associated with high levels of morbidity and mortality. Here, we report the first identified S. aureus factor (lipase 1) that enhances IAV replication during infection via positive modulation of virus budding. The effect is observed in vivo in embryonated hen’s eggs and greatly enhances the yield of a vaccine strain, a finding that could be applied to address global shortages of influenza vaccines.

Influenza A virus (IAV) causes annual epidemics of respiratory disease in humans, often complicated by secondary coinfection with bacterial pathogens such as Staphylococcus aureus. Here, we report that the S. aureus secreted protein lipase 1 enhances IAV replication in vitro in primary cells, including human lung fibroblasts. The proviral activity of lipase 1 is dependent on its enzymatic function, acts late in the viral life cycle, and results in increased infectivity through positive modulation of virus budding. Furthermore, the proviral effect of lipase 1 on IAV is exhibited during in vivo infection of embryonated hen’s eggs and, importantly, increases the yield of a vaccine strain of IAV by approximately 5-fold. Thus, we have identified the first S. aureus protein to enhance IAV replication, suggesting a potential role in coinfection. Importantly, this activity may be harnessed to address global shortages of influenza vaccines.

σB Inhibits Poly-N-Acetylglucosamine Exopolysaccharide Synthesis and Biofilm Formation in Staphylococcus aureus

Staphylococcus aureus clinical strains are able to produce at least two distinct types of biofilm matrixes: biofilm matrixes made of the polysaccharide intercellular adhesin (PIA) or poly-N-acetylglucosamine (PNAG), whose synthesis is mediated by the icaADBC locus, and biofilm matrixes built of proteins (polysaccharide independent). σ^B is a conserved alternative sigma factor that regulates the expression of more than 100 genes in response to changes in environmental conditions. While numerous studies agree that σ^B is required for polysaccharide-independent biofilms, controversy persists over the role of σ^B in the regulation of PIA/PNAG-dependent biofilm development. Here, we show that genetically unrelated S. aureus σ^B-deficient strains produced stronger biofilms under both static and flow conditions and accumulated higher levels of PIA/PNAG exopolysaccharide than their corresponding wild-type strains. The increased accumulation of PIA/PNAG in the σ^B mutants correlated with a greater accumulation of the IcaC protein showed that it was not due to adjustments in icaADBC operon transcription and/or icaADBC mRNA stability. Overall, our results reveal that in the presence of active σ^B, the turnover of Ica proteins is accelerated, reducing the synthesis of PIA/PNAG exopolysaccharide and consequently the PIA/PNAG-dependent biofilm formation capacity.IMPORTANCE Due to its multifaceted lifestyle, Staphylococcus aureus needs a complex regulatory network to connect environmental signals with cellular physiology. One particular transcription factor, named σ^B (SigB), is involved in the general stress response and the expression of virulence factors. For many years, great confusion has existed about the role of σ^B in the regulation of the biofilm lifestyle in S. aureus Our study demonstrated that σ^B is not necessary for exopolysaccharide-dependent biofilms and, even more, that S. aureus produces stronger biofilms in the absence of σ^B The increased accumulation of exopolysaccharide correlates with higher stability of the proteins responsible for its synthesis. The present findings reveal an additional regulatory layer to control biofilm exopolysaccharide synthesis under stress conditions.

Staphylococcus aureus Secreted Toxins and Extracellular Enzymes

Staphylococcus aureus is a formidable pathogen capable of causing infections in different sites of the body in a variety of vertebrate animals, including humans and livestock. A major contribution to the success of S. aureus as a pathogen is the plethora of virulence factors that manipulate the host's innate and adaptive immune responses. Many of these immune modulating virulence factors are secreted toxins, cofactors for activating host zymogens, and exoenzymes. Secreted toxins such as pore-forming toxins and superantigens are highly inflammatory and can cause leukocyte cell death by cytolysis and clonal deletion, respectively. Coagulases and staphylokinases are cofactors that hijack the host's coagulation system. Exoenzymes, including nucleases and proteases, cleave and inactivate various immune defense and surveillance molecules, such as complement factors, antimicrobial peptides, and surface receptors that are important for leukocyte chemotaxis. Additionally, some of these secreted toxins and exoenzymes can cause disruption of endothelial and epithelial barriers through cell lysis and cleavage of junction proteins. A unique feature when examining the repertoire of S. aureus secreted virulence factors is the apparent functional redundancy exhibited by the majority of the toxins and exoenzymes. However, closer examination of each virulence factor revealed that each has unique properties that have important functional consequences. This chapter provides a brief overview of our current understanding of the major secreted virulence factors critical for S. aureus pathogenesis.

Bacterial lipolysis of immune-activating ligands promotes evasion of innate defenses

Commensal and pathogenic bacteria hydrolyze host lipid substrates with secreted lipases and phospholipases for nutrient acquisition, colonization, and infection. Bacterial lipase activity on mammalian lipids and phospholipids can promote release of free fatty acids from lipid stores, detoxify antimicrobial lipids, and facilitate membrane dissolution. The gram-positive bacterium Staphylococcus aureus secretes at least two lipases, Sal1 and glycerol ester hydrolase (Geh), with specificities for short- and long-chain fatty acids, respectively, each with roles in the hydrolysis of environmental lipids. In a recent study from our group, we made the unexpected observation that Geh released by S. aureus inhibits activation of innate immune cells. Herein, we investigated the possibility that S. aureus lipases interface with the host immune system to blunt innate immune recognition of the microbe. We found that the Geh lipase, but not other S. aureus lipases, prevents activation of innate cells in culture. Mutation of geh leads to enhancement of proinflammatory cytokine production during infection, increased innate immune activity, and improved clearance of the bacterium in infected tissue. These in vitro and in vivo effects on innate immunity were not due to direct functions of the lipase on mammalian cells, but rather a result of inactivation of S. aureus lipoproteins, a major pathogen-associated molecular pattern (PAMP) of extracellular gram-positive bacteria, via ester hydrolysis. Altogether, these studies provide insight into an adaptive trait that masks microbial recognition by innate immune cells through targeted inactivation of a broadly conserved PAMP.

Atypical organic-solvent tolerant bacterial hormone sensitive lipase-like homologue EstAG1 from Staphylococcus saprophyticus AG1: Synthesis and characterization

Biocatalysts exerting activity against ester bonds have a broad range of applications in modern biotechnology. Some of the most industrially relevant enzymes of this type are lipolytic and their market is predicted to uphold leadership up till 2024. In this study, a novel bacterial hormone-sensitive lipase-like (bHSL) family homologue, designated EstAG1, was discovered by mining gDNA of bacteria isolated from fat contaminated soil in Lithuania. Putative lipolytic enzyme was cloned, overexpressed in E. coli, purified and characterized determining its biochemical properties. While the true physiological role of the discovered leaderless, ~36 kDa enzyme is unknown, metal-activated EstAG1 possessed optima at 45-47.5 °C, pH 7.5-8, with a generally intermediate activity profile between esterases and lipases. Furthermore, EstAG1 was hyperactivated by ethanol, dioxane and DMSO, implicating that it could be industrially applicable enzyme for the synthesis of valuable products such as biodiesel, flavor esters, etc. Sequence analysis and structure modeling revealed that the highest sequence homology of EstAG1 with the closest structurally and functionally described protein makes up only 26%. It was also revealed that EstAG1 has some differences in the bHSL family-characteristic conserved sequence motives. Therefore, EstAG1 presents interest both in terms of biotechnological applications and basic research.

Staphylococcus aureus Utilizes Host-Derived Lipoprotein Particles as Sources of Fatty Acids

Methicillin-resistant Staphylococcus aureus (MRSA) is a threat to global health. Consequently, much effort has focused on the development of new antimicrobials that target novel aspects of S. aureus physiology. Fatty acids are required to maintain cell viability, and bacteria synthesize fatty acids using the type II fatty acid synthesis (FASII) pathway. FASII is significantly different from human fatty acid synthesis, underscoring the therapeutic potential of inhibiting this pathway. However, many Gram-positive pathogens incorporate exogenous fatty acids, bypassing FASII inhibition and leaving the clinical potential of FASII inhibitors uncertain. Importantly, the source(s) of fatty acids available to pathogens within the host environment remains unclear. Fatty acids are transported throughout the body by lipoprotein particles in the form of triglycerides and esterified cholesterol. Thus, lipoproteins, such as low-density lipoprotein (LDL), represent a potentially rich source of exogenous fatty acids for S. aureus during infection. We sought to test the ability of LDLs to serve as a fatty acid source for S. aureus and show that cells cultured in the presence of human LDLs demonstrate increased tolerance to the FASII inhibitor triclosan. Using mass spectrometry, we observed that host-derived fatty acids present in the LDLs are incorporated into the staphylococcal membrane and that tolerance to triclosan is facilitated by the fatty acid kinase A, FakA, and Geh, a triacylglycerol lipase. Finally, we demonstrate that human LDLs support the growth of S. aureus fatty acid auxotrophs. Together, these results suggest that human lipoprotein particles are a viable source of exogenous fatty acids for S. aureus during infection.IMPORTANCE Inhibition of bacterial fatty acid synthesis is a promising approach to combating infections caused by S. aureus and other human pathogens. However, S. aureus incorporates exogenous fatty acids into its phospholipid bilayer. Therefore, the clinical utility of targeting bacterial fatty acid synthesis is debated. Moreover, the fatty acid reservoir(s) exploited by S. aureus is not well understood. Human low-density lipoprotein particles represent a particularly abundant in vivo source of fatty acids and are present in tissues that S. aureus colonizes. Herein, we establish that S. aureus is capable of utilizing the fatty acids present in low-density lipoproteins to bypass both chemical and genetic inhibition of fatty acid synthesis. These findings imply that S. aureus targets LDLs as a source of fatty acids during pathogenesis.

Staphylococcus carnosus: from starter culture to protein engineering platform

Since the 1950s, Staphylococcus carnosus is used as a starter culture for sausage fermentation where it contributes to food safety, flavor, and a controlled fermentation process. The long experience with S. carnosus has shown that it is a harmless and "food grade" species. This was confirmed by the genome sequence of S. carnosus TM300 that lacks genes involved in pathogenicity. Since the development of a cloning system in TM300, numerous genes have been cloned, expressed, and characterized and in particular, virulence genes that could be functionally validated in this non-pathogenic strain. A secretion system was developed for production and secretion of industrially important proteins and later modified to also enable display of heterologous proteins on the surface. The display system has been employed for various purposes, such as development of live bacterial delivery vehicles as well as microbial biocatalysts or bioadsorbents for potential environmental or biosensor applications. Recently, this surface display system has been utilized for display of peptide and protein libraries for profiling of protease substrates and for generation of various affinity proteins, e.g., Affibody molecules and scFv antibodies. In addition, by display of fragmented antigen-encoding genes, the surface expression system has been successfully used for epitope mapping of antibodies. Reviews on specific applications of S. carnosus have been published earlier, but here we provide a more extensive overview, covering a broad range of areas from food fermentation to sophisticated methods for protein-based drug discovery, which are all based on S. carnosus.

Staphylococcal (phospho)lipases promote biofilm formation and host cell invasion

Most Staphylococcus aureus strains secrete two lipases SAL1 and SAL2 encoded by gehA and gehB. These two lipases differ with respect to their substrate specificity. Staphylococcus hyicus secretes another lipase, SHL, which is in contrast to S. aureus lipases Ca²⁺-dependent and has a broad-spectrum lipase and phospholipase activity. The aim of this study was to investigate the role of staphylococcal (phospho) lipases in virulence. For this we constructed a gehA-gehB double deletion mutant in S. aureus USA300 and expressed SHL in agr-positive (accessory gene regulator) and agr-negative S. aureus strains. The lipases themselves have no hemolytic or cytotoxic activity. However, in agr-negative strains SHL-expression caused an upregulation of hemolytic activity. We further show that SHL-expression significantly enhanced biofilm formation probably due to an increase of extracellular DNA release. SHL-expression also increased host cell invasion 4-6-fold. Trioleate, a main triacylglycerol component of mammalian skin, induced lipase production. Finally, in the mouse sepsis and skin colonization models the lipase producing and mutant strain showed no significant difference compared to the WT strain. In conclusion, we show that staphylococcal lipases promote biofilm formation and host cell invasion and thereby contribute to S. aureus virulence.

A Topical Medication of All-Trans Retinoic Acid Reduces Sebum Excretion Rate in Patients With Forehead Acne

Acne is a disease of the hair follicles of the face, chest, and back that affects almost all teenagers during puberty. This study is conducted to investigate if all-trans retinoic acid (ATRA) could reduce sebum excretion rate (SER) in acne patients by influencing content of skin-surface lipid production. Thirty-nine patients with forehead acne were topically treated with cream base (vehicle) and 0.025% ATRA cream once a night for 7 days. Separation and identification of sebum production collected from the skin on the acne were performed using thin-layer chromatography. SER was calculated according to the total amount of individual sebum productions that were quantified by using Alphaimager IS-2200 imaging analysis. Our data showed that the value of SER on the acne-affected skin was significantly decreased in the ATRA-treated patients as compared with ones treated with vehicle (P < 0.01). Treatment with ATRA resulted in inducing significant decreases in the contents of wax esters (WE), triglycerides and fatty acids, and free fatty acids (FFA) productions (all P < 0.01). In further analysis, the changes in the data before and after treatments with vehicle and ATRA were compared with significant differences exhibited in the values of SER, WE, and FFA (all P < 0.05). This study indicates that the topical application of ATRA in treatment of acne patients induces decrease in SER by inhibiting the excretion of WE and FFA productions.

Classification of lipolytic enzymes and their biotechnological applications in the pulping industry

In the pulp and paper industry, during the manufacturing process, the agglomeration of pitch particles (composed of triglycerides, fatty acids, and esters) leads to the formation of black pitch deposits in the pulp and on machinery, which impacts on the process and pulp quality. Traditional methods of pitch prevention and treatment are no longer feasible due to environmental impact and cost. Consequently, there is a need for more efficient and environmentally friendly approaches. The application of lipolytic enzymes, such as lipases and esterases, could be the sustainable solution to this problem. Therefore, an understanding of their structure, mechanism, and sources are essential. In this report, we review the microbial sources for the different groups of lipolytic enzymes, the differences between lipases and esterases, and their potential applications in the pulping industry.

Novel perspectives on the role of the human microbiota in regenerative medicine and surgery

Plastic surgery is transitioning from a fine craftsmanship to a regenerative science. In wound healing, the role of microorganisms is no longer considered to be just counteracting, but also promoting. Furthermore, host-microbe interactions are essential for numerous aspects of normal mammalian physiology, from metabolic activity to immune homeostasis. Each area of the human body hosts a unique microbial community, and the composition of microbiota is dependent on the host, age and the anatomical area, and it changes according to the characteristics of the microenvironment. Every squared centimeter of skin contains ~1 billion bacteria. The majority of microorganisms of the skin are commensal or temporary passing members. Skin flora mechanisms interacting or influencing the human physical skin barrier are not well defined. Resident skin bacteria provide the first line of defence against potentially dangerous pathogens and produce small molecules that influence their microbial neighbours. Furthermore, the microbiota activates and assists innate immunity and influences adaptive immunity. Various types of immune and non-immune cells contribute to wound healing. The proliferative phase of wound healing is inversely proportional to the extent of the post-traumatic inflammatory reaction. Topical bacterial lipopolysaccharide application markedly affects wound healing by accelerating the resolution of inflammation, increasing macrophage infiltration, enhancing collagen synthesis and altering the secretion of mediators involved in skin regeneration. Various studies have investigated the biological contents of thermal spring waters, and their anti-inflammatory and immune protective roles. In addition, the regenerative properties of thermal spring waters were analysed in an experimental animal wound model. The areas treated with thermal water healed faster than the areas treated with conventional dressings, and exhibited a collagen and elastic fiber network comparable with the normal skin. Thus, the microbial environment may be considered as a potential tool in regenerative medicine and surgery.

Skin-Specific Unsaturated Fatty Acids Boost the Staphylococcus aureus Innate Immune Response

Antimicrobial fatty acids (AFAs) protect the human epidermis against invasion by pathogenic bacteria. In this study, we questioned whether human skin fatty acids (FAs) can be incorporated into the lipid moiety of lipoproteins and whether such incorporation would have an impact on innate immune stimulation in the model organism Staphylococcus aureus USA300 JE2. This organism synthesized only saturated FAs. However, when feeding USA300 with unsaturated FAs present on human skin (C16:1, C18:1, or C18:2), those were taken up, elongated stepwise by two carbon units, and finally found in the bacterial (phospho)lipid fraction. They were also observed in the lipid moiety of lipoproteins. When USA300 JE2 was fed with the unsaturated FAs, the cells and cell lysates showed an increased innate immune activation with various immune cells and peripheral blood mononuclear cells (PBMCs). Immune activation was highest with linoleic acid (C18:2). There are several pieces of evidence that the enhanced immune stimulating effect was due to the incorporation of unsaturated FAs in lipoproteins. First, the enhanced stimulation was dependent on Toll-like receptor 2 (TLR2). Second, an lgt mutant, unable to carry out lipidation of prolipoproteins, was unable to carry out immune stimulation when fed with unsaturated FAs. Third, the supplied FAs did not significantly affect growth, protein release, or expression of the model lipoprotein Lpl1. Although S. aureus is unable to synthesize unsaturated FAs, it incorporates long-chain unsaturated FAs into its lipoproteins, with the effect that the cells are better recognized by the innate immune system. This is an additional mechanism how our skin controls bacterial colonization and infection.

An efficient system for intracellular delivery of beta-lactam antibiotics to overcome bacterial resistance

The "Golden era" of antibiotics is definitely an old story and this is especially true for intracellular bacterial infections. The poor intracellular bioavailability of antibiotics reduces the efficency of many treatments and thereby promotes resistances. Therefore, the development of nanodevices coupled with antibiotics that are capable of targeting and releasing the drug into the infected-cells appears to be a promising solution to circumvent these complications. Here, we took advantage of two natural terpenes (farnesyl and geranyl) to design nanodevices for an efficient intracellular delivery of penicillin G. The covalent linkage between the terpene moieties and the antibiotic leads to formation of prodrugs that self-assemble to form nanoparticles with a high drug payload between 55-63%. Futhermore, the addition of an environmentally-sensitive bond between the antibiotic and the terpene led to an efficient antibacterial activity against the intracellular pathogen Staphylococcus aureus with reduced intracellular replication of about 99.9% compared to untreated infected cells. Using HPLC analysis, we demonstrated and quantified the intracellular release of PenG when this sensitive-bond (SB) was present on the prodrug, showing the success of this technology to deliver antibiotics directly into cells.

Role of lipase from community-associated methicillin-resistant Staphylococcus aureus strain USA300 in hydrolyzing triglycerides into growth-inhibitory free fatty acids

Part of the human host innate immune response involves the secretion of bactericidal lipids on the skin and delivery of triglycerides into abscesses to control invading pathogens. Two Staphylococcus aureus lipases, named SAL1 and SAL2, were identified in the community-associated methicillin-resistant S. aureus strain USA300, which, presumably, are produced and function to degrade triglycerides to release free fatty acids. We show that the SAL2 lipase is one of the most abundant proteins secreted by USA300 and is proteolytically processed from the 72-kDa proSAL2 to the 44-kDa mature SAL2 by the metalloprotease aureolysin. We show that spent culture supernatants had lipase activity on both short- and long-chain fatty acid substrates and that deletion of gehB, encoding SAL2, resulted in the complete loss of these activities. With the use of gas chromatography-mass spectrometry, we show that SAL2 hydrolyzed trilinolein to linoleic acid, a fatty acid with known antistaphylococcal properties. When added to cultures of USA300, trilinolein and, to a lesser extent, triolein inhibited growth in a SAL2-dependent manner. This effect was shown to be due to the enzymatic activity of SAL2 on these triglycerides, since the catalytically inactive SAL2 Ser412Ala mutant was incapable of hydrolyzing the triglycerides or yielding delayed growth in their presence. Overall, these results reveal that SAL2 hydrolyzes triglycerides of both short- and long-chain fatty acids and that the released free fatty acids have the potential to cause significant delays in growth, depending on the chemical nature of the free fatty acid.

The skin microbiome: current perspectives and future challenges

Complex communities of bacteria, fungi, and viruses thrive on our skin. The composition of these communities depends on skin characteristics, such as sebaceous gland concentration, moisture content, and temperature, as well as on host genetics and exogenous environmental factors. Recent metagenomic studies have uncovered a surprising diversity within these ecosystems and have fostered a new view of commensal organisms as playing a much larger role in immune modulation and epithelial health than previously expected. Understanding microbe-host interactions and discovering the factors that drive microbial colonization will help us understand the pathogenesis of skin diseases and develop new promicrobial and antimicrobial therapeutics.

Bap, a biofilm matrix protein of Staphylococcus aureus prevents cellular internalization through binding to GP96 host receptor

The biofilm matrix, composed of exopolysaccharides, proteins, nucleic acids and lipids, plays a well-known role as a defence structure, protecting bacteria from the host immune system and antimicrobial therapy. However, little is known about its responsibility in the interaction of biofilm cells with host tissues. Staphylococcus aureus, a leading cause of biofilm-associated chronic infections, is able to develop a biofilm built on a proteinaceous Bap-mediated matrix. Here, we used the Bap protein as a model to investigate the role that components of the biofilm matrix play in the interaction of S. aureus with host cells. The results show that Bap promotes the adhesion but prevents the entry of S. aureus into epithelial cells. A broad analysis of potential interaction partners for Bap using ligand overlayer immunoblotting, immunoprecipitation with purified Bap and pull down with intact bacteria, identified a direct binding between Bap and Gp96/GRP94/Hsp90 protein. The interaction of Bap with Gp96 provokes a significant reduction in the capacity of S. aureus to invade epithelial cells by interfering with the fibronectin binding protein invasion pathway. Consistent with these results, Bap deficient bacteria displayed an enhanced capacity to invade mammary gland epithelial cells in a lactating mice mastitis model. Our observations begin to elucidate the mechanisms by which components of the biofilm matrix can facilitate the colonization of host tissues and the establishment of persistent infections.

Protease-armed bacteria in the skin

The skin constitutes a formidable barrier against commensal and pathogenic bacteria, which permanently and transiently colonise the skin, respectively. Commensal and pathogenic species inhabiting skin both express proteases. Whereas proteases secreted by commensals contribute to homeostatic bacterial coexistence on skin, proteases from pathogenic bacteria are used as virulence factors, helping them colonise skin with breached integrity of the epithelial layer. From these initial sites of colonisation, pathogens can disseminate into deeper layers of skin, possibly leading to the spread of infection. Secreted bacterial proteases probably play an important role in this process and in the deterrence of innate defence mechanisms. For example, Staphylococcus aureus proteases are essential for changing the bacterial phenotype from adhesive to invasive by degrading adhesins on the bacterial cell surface. Secreted staphylococcal proteases mediate pathogen penetration by degrading collagen and elastin, essential components of connective tissue in the dermis. The activation of the contact system and kinin generation by Streptococcus pyogenes and S. aureus proteases contributes to an inflammatory reaction manifested by oedema, redness and pain. Kinin-enhanced vascular leakage might help bacteria escape into the circulation thereby causing possible systemic dissemination of the infection. The inflammatory reaction can also be fueled by the activation of protease-activated receptors on keratinocytes. Concomitantly, bacterial proteases are involved in degrading antimicrobial peptides, disarming the complement system and neutrophils and preventing the infiltration of the infected sites with immune cells by inactivation of chemoattractants. Together, this provides protection for colonising and/or invading pathogens from attack by antibacterial forces of the skin.

Microbial symbiosis with the innate immune defense system of the skin

Skin protects itself against infection through a variety of mechanisms. Antimicrobial peptides (AMPs) are major contributors to cutaneous innate immunity, and this system, combined with the unique ionic, lipid and physical barrier of the epidermis is the first line defense against invading pathogens. However, recent studies have revealed that our skin’s innate immune system is not solely of human origin. Staphylococcus epidermidis, a major constituent of the normal microflora on healthy human skin, acts as a barrier against colonization of potentially pathogenic microbes and against overgrowth of already present opportunistic pathogens. Our resident commensal microbes produce their own AMPs, act to enhance the normal production of AMPs by keratinocytes, and are beneficial to maintaining inflammatory homeostasis by suppressing excess cytokine release after minor epidermal injury. These observations indicate that the normal human skin microflora protects skin via various modes of action, a conclusion supported by many lines of evidence associating diseases such as acne, atopic dermatitis, psoriasis and rosacea with an imbalance of the microflora even in the absence of classical infection. This review highlights recent observations on the importance of innate immune systems and the relationship with the normal skin microflora to maintain healthy skin.

The Staphylococcus aureus lipoprotein SitC colocalizes with Toll-like receptor 2 (TLR2) in murine keratinocytes and elicits intracellular TLR2 accumulation

SitC is one of the predominant lipoproteins in Staphylococcus aureus. Recently, SitC was shown to be capable of stimulating Toll-like receptor 2 (TLR2), but the mechanism of TLR2 activation by SitC has not been analyzed in detail so far. In this study, we purified C-terminally His-tagged SitC (SitC-His) from Staphylococcus aureus. SitC-His induced interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) release in human monocytes and also NF-κB activation in TLR2-transfected HEK293 cells, indicating TLR2-specific activation. SitC not only induced a TLR2-dependent release of IL-6 in primary murine keratinocytes (MKs) but also induced intracellular accumulation of TLR2, which was time and concentration dependent. Cy2-labeled SitC-His colocalized specifically with TLR2 in MKs and was also internalized in TLR2 knockout MKs, suggesting a TLR2-independent uptake. Neither activation nor colocalization of SitC-His was observed with TLR4 or Nod2. The results show that the native lipoprotein SitC-His specifically colocalizes with TLR2, is internalized by host cells, induces proinflammatory cytokines, and triggers intracellular accumulation of TLR2.

Comprehensive characterization of methicillin-resistant Staphylococcus aureus subsp. aureus COL secretome by two-dimensional liquid chromatography and mass spectrometry

Two-dimensional LC combined with whole protein and peptide mass spectrometry is used to characterize proteins secreted by methicillin-resistant Staphylococcus aureus COL. Protein identifications were accomplished via off-line protein fractionation followed by digestion and subsequent peptide analysis by reverse phase LC-ESI-LTQ-FT-MS/MS. Peptide MS/MS analysis identified 127 proteins comprising 59 secreted proteins, seven cell wall-anchored proteins, four lipoproteins, four membrane proteins, and 53 cytoplasmic proteins. The identified secreted proteins included various virulence factors of known functions (cytotoxins, enterotoxins, proteases, lipolytic enzymes, peptidoglycan hydrolases, etc.). Accurate whole protein mass measurement (+/-1.5 Da) of the secreted proteins combined with peptide analysis enabled identification of signal peptide cleavage sites and various post-translational modifications. In addition, new observations were possible using the present approach. Although signal peptide cleavage is highly specific, signal peptide processing can occur at more than one site. Surprisingly, cleaved signal peptides and their fragments can be observed in the extracellular medium. The prediction accuracies of several signal peptide prediction programs were also evaluated.

Sebum free fatty acids enhance the innate immune defense of human sebocytes by upregulating beta-defensin-2 expression

Various sebum free fatty acids (FFAs) have shown antibacterial activity against a broad range of gram-positive bacteria, resulting in the suggestion that they are accountable, at least partially, for the direct antimicrobial activity of the skin surface. In this study, we examined the effects of sebum FFAs on the antimicrobial peptide (AMP)-mediated innate immune defense of human sebocytes. Incubation of lauric acid, palmitic acid, or oleic acid (OA) with human sebocytes dramatically enhanced their expression of human beta-defensin (hBD)-2, one of the predominant AMPs found in the skin, whereas remarkable increases in hBD-1, hBD-3, and human cathelicidin LL-37 were not observed. Secreted hBD-2 was detectable by western blotting in the supernatant of sebocyte culture incubated with each FFA, but not with a vehicle control. The supernatant of FFA-incubated sebocyte culture showed antimicrobial activity against Propionibacterium acnes, whereas the enhanced antimicrobial activity of human sebocytes was neutralized by anti-hBD-2 IgG. In addition, the FFA-induced hBD-2 expression was suppressed by blocking the cluster of differentiation (CD)36 fatty acid translocase on the surface of sebocytes with anti-human CD36 IgG or blocking the NF-kappaB signaling pathway with BMS-345541, a highly selective inhibitor of inhibitory kappaB kinase. These data suggest that sebum FFAs upregulate the expression of hBD-2 in human sebocytes, which may enhance the disinfecting activity of the human sebaceous gland. The FFA-induced upregulation of hBD-2 is facilitated by CD36-mediated FFA uptake and NF-kappaB-mediated transactivation. The upregulation of mouse beta-defensin 4, a mouse ortholog for hBD-2, was also observed in the hair follicle sebaceous glands of mouse ear skin after an epicutaneous application of OA, the most hBD-2-inducible FFA tested. This report highlights the potential of using FFAs as a multifunctional antimicrobial therapy agent for acne vulgaris treatment; FFAs may provide direct antibacterial activities against P. acnes and enhance the skin's innate antibacterial defense by inducing the expression of hBD-2 in sebocytes as well.

Contributions of the pre- and pro-regions of a Staphylococcus hyicus lipase to secretion of a heterologous protein by Bacillus subtilis

Bacillus subtilis is a well-established cell factory for efficient secretion of many biotechnologically relevant enzymes that are naturally produced by it or related organisms. However, the use of B. subtilis as a host for production of heterologous secretory proteins can be complicated by problems related to inefficient translocation of the foreign proteins across the plasma membrane or to inefficient release of the exported proteins from the cell surface into the surrounding medium. Therefore, there is a clear need for tools that allow more efficient membrane targeting, translocation, and release during the production of these proteins. In the present study, we investigated the contributions of the pre (pre(lip)) and pro (pro(lip)) sequences of a Staphylococcus hyicus lipase to secretion of a heterologous protein, the alkaline phosphatase PhoA of Escherichia coli, by B. subtilis. The results indicate that the presence of the pro(lip)-peptide, in combination with the lipase signal peptide (pre(lip)), contributes significantly to the efficient secretion of PhoA by B. subtilis and that pre(lip) directs PhoA secretion more efficiently than the authentic signal peptide of PhoA. Genome-wide transcriptional analyses of the host cell responses indicate that, under the conditions tested, no known secretion or membrane-cell wall stress responses were provoked by the production of PhoA with any of the pre- and pro-region sequences used. Our data underscore the view that the pre-pro signals of the S. hyicus lipase are very useful tools for secretion of heterologous proteins in B. subtilis.

Role of the twin-arginine translocation pathway in Staphylococcus

In Staphylococcus, the twin-arginine translocation (Tat) pathway is present only in some species and is composed of TatA and TatC. The tatAC operon is associated with the fepABC operon, which encodes homologs to an iron-binding lipoprotein, an iron-dependent peroxidase (FepB), and a high-affinity iron permease. The FepB protein has a typical twin-arginine (RR) signal peptide. The tat and fep operons constitute an entity that is not present in all staphylococcal species. Our analysis was focused on Staphylococcus aureus and S. carnosus strains. Tat deletion mutants (DeltatatAC) were unable to export active FepB, indicating that this enzyme is a Tat substrate. When the RR signal sequence from FepB was fused to prolipase and protein A, their export became Tat dependent. Since no other protein with a Tat signal could be detected, the fepABC-tatAC genes comprise not only a genetic but also a functional unit. We demonstrated that FepABC drives iron import, and in a mouse kidney abscess model, the bacterial loads of DeltatatAC and Deltatat-fep mutants were decreased. For the first time, we show that the Tat pathway in S. aureus is functional and serves to translocate the iron-dependent peroxidase FepB.

Structure of the alkalohyperthermophilic Archaeoglobus fulgidus lipase contains a unique C-terminal domain essential for long-chain substrate binding

Several crystal structures of AFL, a novel lipase from the archaeon Archaeoglobus fulgidus, complexed with various ligands, have been determined at about 1.8 A resolution. This enzyme has optimal activity in the temperature range of 70-90 degrees C and pH 10-11. AFL consists of an N-terminal alpha/beta-hydrolase fold domain, a small lid domain, and a C-terminal beta-barrel domain. The N-terminal catalytic domain consists of a 6-stranded beta-sheet flanked by seven alpha-helices, four on one side and three on the other side. The C-terminal lipid binding domain consists of a beta-sheet of 14 strands and a substrate covering motif on top of the highly hydrophobic substrate binding site. The catalytic triad residues (Ser136, Asp163, and His210) and the residues forming the oxyanion hole (Leu31 and Met137) are in positions similar to those of other lipases. Long-chain lipid is located across the two domains in the AFL-substrate complex. Structural comparison of the catalytic domain of AFL with a homologous lipase from Bacillus subtilis reveals an opposite substrate binding orientation in the two enzymes. AFL has a higher preference toward long-chain substrates whose binding site is provided by a hydrophobic tunnel in the C-terminal domain. The unusually large interacting surface area between the two domains may contribute to thermostability of the enzyme. Two amino acids, Asp61 and Lys101, are identified as hinge residues regulating movement of the lid domain. The hydrogen-bonding pattern associated with these two residues is pH dependent, which may account for the optimal enzyme activity at high pH. Further engineering of this novel lipase with high temperature and alkaline stability will find its use in industrial applications.

Agr-mediated dispersal of Staphylococcus aureus biofilms

The agr quorum-sensing system of Staphylococcus aureus modulates the expression of virulence factors in response to autoinducing peptides (AIPs). Recent studies have suggested a role for the agr system in S. aureus biofilm development, as agr mutants exhibit a high propensity to form biofilms, and cells dispersing from a biofilm have been observed displaying an active agr system. Here, we report that repression of agr is necessary to form a biofilm and that reactivation of agr in established biofilms through AIP addition or glucose depletion triggers detachment. Inhibitory AIP molecules did not induce detachment and an agr mutant was non-responsive, indicating a dependence on a functional, active agr system for dispersal. Biofilm detachment occurred in multiple S. aureus strains possessing divergent agr systems, suggesting it is a general S. aureus phenomenon. Importantly, detachment also restored sensitivity of the dispersed cells to the antibiotic rifampicin. Proteinase K inhibited biofilm formation and dispersed established biofilms, suggesting agr-mediated detachment occurred in an ica-independent manner. Consistent with a protease-mediated mechanism, increased levels of serine proteases were detected in detaching biofilm effluents, and the serine protease inhibitor PMSF reduced the degree of agr-mediated detachment. Through genetic analysis, a double mutant in the agr-regulated Aur metalloprotease and the SplABCDEF serine proteases displayed minimal extracellular protease activity, improved biofilm formation, and a strongly attenuated detachment phenotype. These findings indicate that induction of the agr system in established S. aureus biofilms detaches cells and demonstrate that the dispersal mechanism requires extracellular protease activity.

A biofilm is a surface-attached community of cells bound together by an extracellular matrix. In a bacterial infection, biofilm-encased cells are protected from antibiotic therapy and host immune response, and these encased cells can develop into a chronic infection. Staphylococcus aureus is a prominent bacterial pathogen known to form biofilms on many medical implants and host tissues. In this report, we demonstrate that repression of the S. aureus quorum-sensing system is required to form a biofilm, and quorum-sensing reactivation in established biofilms disperses the cells. Genetic and molecular analysis demonstrates that quorum-sensing is activated before and required for the detachment mechanism. Detachment is protease-mediated, as established biofilms are sensitive to a non-specific protease and quorum-sensing activation increases the production of extracellular proteases. Using mutations in the protease genes, we show that these secreted enzymes are required for the detachment mechanism. These findings denote that S. aureus quorum-sensing can function as a dispersal mechanism to colonize new sites, and our results suggest this mechanism could be modulated to treat recalcitrant biofilms.

Purification and characterization of two highly thermophilic alkaline lipases from Thermosyntropha lipolytica

Two thermostable lipases were isolated and characterized from Thermosyntropha lipolytica DSM 11003, an anaerobic, thermophilic, alkali-tolerant bacterium which grows syntrophically with methanogens on lipids such as olive oil, utilizing only the liberated fatty acid moieties but not the glycerol. Lipases LipA and LipB were purified from culture supernatants to gel electrophoretic homogeneity by ammonium sulfate precipitation and hydrophobic interaction column chromatography. The apparent molecular masses of LipA and LipB determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were 50 and 57 kDa, respectively. The temperature for maximal activity of LipA and LipB was around 96 degrees C, which is, so far as is known, the highest temperature for maximal activity among lipases, and the pH optima for growth determined at 25 degrees C (pH(25 degrees C) optima) were 9.4 and 9.6, respectively. LipA and LipB at 100 degrees C and pH(25 degrees C) 8.0 retained 50% activity after 6 and 2 h of incubation, respectively. Both enzymes exhibited high activity with long-chain fatty acid glycerides, yielding maximum activity with trioleate (C(18:1)) and, among the p-nitrophenyl esters, with p-nitrophenyl laurate. Hydrolysis of glycerol ester bonds occurred at positions 1 and 3. The activities of both lipases were totally inhibited by 10 mM phenylmethylsulfonyl fluoride and 10 mM EDTA. Metal analysis indicated that both LipA and LipB contain 1 Ca2+ and one Mn2+ ion per monomeric enzyme unit. The addition of 1 mM MnCl2 to dialyzed enzyme preparations enhanced the activities at 96 degrees C of both LipA and LipB by threefold and increased the durations of their thermal stability at 60 degrees C and 75 degrees C, respectively, by 4 h.

The future of antibody therapy

Antibodies have been used successfully as therapeutics for over 100 years. The successful development of therapeutic human(ized) monoclonal antibodies (mAbs) in the last 20 years has demonstrated the potency of mAbs but also revealed some of their limitations. Studies in animals and humans demonstrated that it is possible to overcome some of these limitations using mixtures of mAbs or polyclonal antibody (pAb) preparations. pAbs from human and animal plasma are efficacious and safe therapeutics for the treatment of many diseases. Novel technologies are being developed for the production of human pAbs in genetically engineered animals. Immunization of such animals should allow the production of effective and safe high-titer antibody preparations for the treatment of infectious diseases, cancer, and autoimmunity.

Sesquiterpene farnesol as a competitive inhibitor of lipase activity ofStaphylococcus aureus

Staphylococcus aureus lipase (SAL) is known to possess broad substrate specificity for triacylglycerides. We found that a sub-minimum inhibitory concentration of farnesol (1000 mg L(-1)) inhibits this lipase activity on a Mueller-Hinton agar containing 1% Tween substrates. A quantitative lipase assay using p-nitrophenyl palmitate (pNPP) revealed that the inhibitory action of farnesol appears to be the result of the inhibition of lipase activity rather than of its secretion into the culture medium. The inhibition was observed in all the tested 8 methicillin-susceptible S. aureus and 31 methicillin-resistant S. aureus clinical isolates. Using homogeneous lipase purified by hydrophobic interaction chromatography, it was revealed that farnesol could competitively inhibit the lipase activity against the substrate pNPP.

Structural Basis of Phospholipase Activity of Staphylococcus hyicus lipase

Staphylococcus hyicus lipase differs from other bacterial lipases in its high phospholipase A1 activity. Here, we present the crystal structure of the S. hyicus lipase at 2.86 A resolution. The lipase is in an open conformation, with the active site partly covered by a neighbouring molecule. Ser124, Asp314 and His355 form the catalytic triad. The substrate-binding cavity contains two large hydrophobic acyl chain-binding pockets and a shallow and more polar third pocket that is capable of binding either a (short) fatty acid or a phospholipid head-group. A model of a phospholipid bound in the active site shows that Lys295 is at hydrogen bonding distance from the substrate's phosphate group. Residues Ser356, Glu292 and Thr294 hold the lysine in position by hydrogen bonding and electrostatic interactions. These observations explain the biochemical data showing the importance of Lys295 and Ser356 for phospholipid binding and phospholipase A1 activity.

The yjeQ gene is required for virulence of Staphylococcus aureus

Gene products required for in vivo growth and survival of Staphylococcus aureus and other pathogens represent new targets for antimicrobial chemotherapy. In this study we created a Staphylococcus aureus yjeQ deletion strain and tested its virulence using a mouse kidney abscess infection model. The yjeQ deletion strain was compromised for growth in vitro and severely attenuated for virulence. We concluded that yjeQ is an attractive and novel new drug target.

MELDB: a database for microbial esterases and lipases

MELDB is a comprehensive protein database of microbial esterases and lipases which are hydrolytic enzymes important in the modern industry. Proteins in MELDB are clustered into groups according to their sequence similarities based on a local pairwise alignment algorithm and a graph clustering algorithm (TribeMCL). This differs from traditional approaches that use global pairwise alignment and joining methods. Our procedure was able to reduce the noise caused by dubious alignment in the distantly related or unrelated regions in the sequences. In the database, 883 esterase and lipase sequences derived from microbial sources are deposited and conserved parts of each protein are identified. HMM profiles of each cluster were generated to classify unknown sequences. Contents of the database can be keyword-searched and query sequences can be aligned to sequence profiles and sequences themselves.

Poly-N-acetylglucosamine production in Staphylococcus aureus is essential for virulence in murine models of systemic infection

The contribution of the Staphylococcus aureus surface polysaccharide poly-N-acetylglucosamine (PNAG) to virulence was evaluated in three mouse models of systemic infection: bacteremia, renal abscess formation, and lethality following high-dose intraperitoneal (i.p.) infection. Deletion of the intercellular adhesin (ica) locus that encodes the biosynthetic enzymes for PNAG production in S. aureus strains Mn8, Newman, and NCTC 10833 resulted in mutant strains with significantly reduced abilities to maintain bacterial levels in blood following intravenous or i.p. injection, to spread systemically to the kidneys following i.p. injection, or to induce a moribund/lethal state following i.p. infection. In the bacteremia model, neither growth phase nor growth medium used to prepare the S. aureus inoculum affected the conclusion that PNAG production was needed for full virulence. As the SarA regulatory protein has been shown to affect ica transcription, PNAG synthesis, and biofilm formation, we also evaluated S. aureus strains Mn8 and 10833 deleted for the sarA gene in the renal infection model. A decrease in PNAG production was seen in sarA mutants using immunoblots of cell surface extracts but was insufficient to reduce the virulence of sarA-deleted strains in this model. S. aureus strains deleted for the ica genes were much more susceptible to antibody-independent opsonic killing involving human peripheral blood leukocytes and rabbit complement. Thus, PNAG confers on S. aureus resistance to killing mediated by these innate host immune mediators. Overall, PNAG production by S. aureus appears to be a critical virulence factor as assessed in murine models of systemic infection.

The surface-associated protein of Staphylococcus saprophyticus is a lipase

Staphylococcus saprophyticus surface-associated protein (Ssp) was the first surface protein described for this organism. Ssp-positive strains display a fuzzy layer of surface-associated material in electron micrographs, whereas Ssp-negative strains appear to be smooth. The physiologic function of Ssp, however, has remained elusive. To clone the associated gene, we determined the N-terminal sequence, as well as an internal amino acid sequence, of the purified protein. We derived two degenerate primers from these peptide sequences, which we used to identify the ssp gene from genomic DNA of S. saprophyticus 7108. The gene was cloned by PCR techniques and was found to be homologous to genes encoding staphylococcal lipases. In keeping with this finding, strains 7108 and 9325, which are Ssp positive, showed lipase activity on tributyrylglycerol agar plates, whereas the Ssp-negative strain CCM883 did not. Association of enzyme activity with the cloned DNA was proven by introducing the gene into Staphylococcus carnosus TM300. When wild-type strain 7108 and an isogenic mutant were analyzed by transmission electron microscopy, strain 7108 exhibited the fuzzy surface layer, whereas the mutant appeared to be smooth. Lipase activity and the surface appendages could be restored by reintroduction of the cloned gene into the mutant. Experiments using immobilized collagen type I did not provide evidence for the involvement of Ssp in adherence to this matrix protein. Our experiments thus provided evidence that Ssp is a surface-associated lipase of S. saprophyticus.

Is the GehD lipase from Staphylococcus epidermidis a collagen binding adhesin?

The opportunistic human pathogen Staphylococcus epidermidis is the major cause of nosocomial biomaterial infections. S. epidermidis has the ability to attach to indwelling materials coated with extracellular matrix proteins such as fibrinogen, fibronectin, vitronectin, and collagen. To identify the proteins necessary for S. epidermidis attachment to collagen, we screened an expression library using digoxigenin-labeled collagen as well as two monoclonal antibodies generated against the Staphylococcus aureus collagen-adhesin, Cna, as probes. These monoclonal antibodies recognize collagen binding epitopes on the surface of S. aureus and S. epidermidis cells. Using this approach, we identified GehD, the extracellular lipase originally found in S. epidermidis 9, as a collagen-binding protein. Despite the monoclonal antibody cross-reactivity, the GehD amino acid sequence and predicted structure are radically different from those of Cna. The mature GehD circular dichroism spectra differs from that of Cna but strongly resembles that of a mammalian cell-surface collagen binding receptor, known as the alpha(1) integrin I domain, suggesting that they have similar secondary structures. The GehD protein is translated as a preproenzyme, secreted, and post-translationally processed into mature lipase. GehD does not have the conserved LPXTG C-terminal motif present in cell wall-anchored proteins, but it can be detected in lysostaphin cell wall extracts. A recombinant version of mature GehD binds to collagens type I, II, and IV adsorbed onto microtiter plates in a dose-dependent saturable manner. Recombinant, mature GehD protein and anti-GehD antibodies can inhibit the attachment of S. epidermidis to immobilized collagen. These results provide evidence that GehD may be a bi-functional molecule, acting not only as a lipase but also as a cell surface-associated collagen adhesin.

Strain-dependent differences in the regulatory roles of sarA and agr in Staphylococcus aureus

The accessory gene regulator (agr) and the staphylococcal accessory regulator (sar) are central regulatory elements that control the production of Staphylococcus aureus virulence factors. To date, the functions of these loci have been defined almost exclusively using RN6390, which is representative of the laboratory strain 8325-4. However, RN6390 was recently shown to have a mutation in rsbU that results in a phenotype resembling that of a sigB mutant (I. Kullik et al., J. Bacteriol. 180:4814-4820, 1998). For that reason, it remains unclear whether the regulatory events defined in RN6390 are representative of the events that take place in clinical isolates of S. aureus. To address this issue, we generated mutations in the sarA and agr loci of three laboratory strains (RN6390, Newman, and S6C) and four clinical isolates (UAMS-1, UAMS-601, DB, and SC-1). Mutation of sarA in the cna-positive strains UAMS-1 and UAMS-601 resulted in an increased capacity to bind collagen, while mutation of agr had little impact. Northern blot analysis confirmed that the increase in collagen binding was due to increased cna transcription. Without exception, mutation of sarA resulted in increased production of proteases and a decreased capacity to bind fibronectin. Mutation of agr had the opposite effect. Although mutation of sarA resulted in a slight reduction in fnbA transcription, changes in the ability to bind fibronectin appeared to be more directly correlated with changes in protease activity. Lipase production was reduced in both sarA and agr mutants. While mutation of sarA in RN6390 resulted in reduced hemolytic activity, it had the opposite effect in all other strains. There appeared to be reduced levels of the sarC transcript in RN6390, but there was no difference in the overall pattern of sar transcription or the production of SarA. Although mutation of sarA resulted in decreased RNAIII transcription, this effect was not evident under all growth conditions. Taken together, these results suggest that studies defining the regulatory roles of sarA and agr by using RN6390 are not always representative of the events that occur in clinical isolates of S. aureus.

Identification of the sigB operon in Staphylococcus epidermidis: construction and characterization of a sigB deletion mutant

The role of the alternative sigma factor sigma(B) in Staphylococcus epidermidis was investigated by the construction, complementation, and characterization of a sigB deletion mutant. Electrophoretic analyses confirmed a profound influence of sigma(B) on the expression of exoproteins and cytoplasmic proteins. Detailed investigation revealed reduced lipase and enhanced protease activity in the sigma(B) mutant. Furthermore, no significant influence of sigma(B) on heterologous biofilm formation or on the activity of the global regulator agr was detected.

Staphylococcal lipases: biochemical and molecular characterization

To date, the nucleotide sequences of nine different lipase genes from six Staphylococcus species, three from S. epidermidis, two from S. aureus, and one each from S. haemolyticus, S. hyicus, S. warneri, and S. xylosus, have been determined. All deduced lipase proteins are similarly organized as pre-pro-proteins, with pre-regions corresponding to a signal peptide of 35 to 38 amino acids, a pro-peptide of 207 to 321 amino acids with an overall hydrophilic character, and a mature peptide comprising 383 to 396 amino acids. The lipases are secreted in the pro-form and are afterwards processed to the mature form by specific proteases. The pro-peptide of the S. hyicus lipase is necessary for efficient translocation and for protection against proteolytic degradation. Despite being very similar in their primary structures the staphylococcal lipases show significant differences in their biochemical and catalytic properties, such as substrate selectivity, pH optimum and interfacial activation. The lipase from S. hyicus is unique among the staphylococcal and bacterial lipases in that it has not only lipase activity, but also a high phospho-lipase activity. All staphylococcal lipases are dependent on Ca(2+), which is thought to have a function in stabilizing the tertiary structure of the lipases. Evidence exists that staphylococcal lipases like other bacterial lipases, possess a lid-like domain that might be involved in the interfacial activation of these enzymes.

Construction and characterization of an agr deletion mutant of Staphylococcus epidermidis

The physiological significance of the accessory gene regulator (agr) system of Staphylococcus epidermidis was investigated by construction of an agr deletion mutant via allelic replacement with a spectinomycin resistance cassette. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the protein pattern was strongly altered in the mutant; the amounts of most surface proteins were higher, whereas the amounts of most exoproteins were lower. The agr system of S. epidermidis thus appears to have an important impact on growth phase-dependent protein synthesis as has been shown for Staphylococcus aureus. The activity of the exoenzymes lipase and protease, assumed to be involved in staphylococcal pathogenicity, was investigated by agar diffusion assays and SDS-PAGE activity staining. A general reduction of these enzyme activities in the agr mutant was found. The difference in overall lipase activity was small, but zymographic analysis suggested a clear defect in lipase processing in the agr mutant.