Apolipoprotein B Is an innate barrier against invasive Staphylococcus aureus infection

Identification of staphylococcal lipoteichoic acid-binding proteins in human serum by high-resolution LTQ-Orbitrap mass spectrometry

Lipoteichoic acid (LTA), a major virulence factor of Gram-positive bacteria, is associated with bacterial adherence to host cells, biofilm formation, and inflammation. LTA-binding proteins (LTA-BPs) play an important role in the host immune response by initially recognizing and responding to LTA during infections. In this study, we screened for LTA-BPs in human serum using LTA-immobilized beads and high-throughput mass spectrometry. Highly pure and structurally intact LTA was prepared from Staphylococcus aureus and immobilized onto N-hydroxysuccinimide-activated Sepharose(®) 4 Fast Flow beads. The immobilization process does not seem to affect the biological activity of LTA since LTA-immobilized beads could stimulate macrophages and activate Toll-like receptor 2. Then, the LTA-immobilized beads were incubated with the human serum to capture LTA-BPs and their molecular identities were determined using high-resolution LTQ-Orbitrap hybrid Fourier transform mass spectrometry. LTA-BPs captured at high frequencies were neutrophil-activating peptide 2, prohibitin-2, alpha-1-anti-trypsin, histidine-rich glycoprotein, apolipoproteins, complements, and coagulation factor, most of which are known to be related with the host immune responses against infections. As high-throughput, efficient, accurate and sensitive, this screening method could be widely applicable to the identification of novel binding proteins to microbial virulence factors with glycolipid structures.

Label-free critical micelle concentration determination of bacterial quorum sensing molecules

A practical label-free method for the rapid determination of small-molecule critical micelle concentration (CMC) using a fixed-angle light-scattering technique is described. Change in 90° light scattering at a fixed wavelength of incident radiation with increasing bacterial quorum molecule concentration and the observation of a break point is used to determine CMC. In our study, this technique is utilized to investigate the aqueous CMC of previously uncharacterized Pseudomonas aeruginosa quorum sensing signaling molecules (QSSM) belonging to the n-acylhomoserine lactone and 2-alkyl-4-quinolone classes. Several were found to form micelles within a physiologically relevant concentration range and potential roles of these micelles as QSSM transporters are discussed. The influence of temperature and the presence of biological membranes or serum proteins on QSSM CMC are also investigated and evidence is obtained to suggest the QSSMs studied are capable of both membrane and serum protein interaction. This demonstrates that the fixed-angle light-scattering technique outlined can be used simply and rapidly to determine small-molecule CMC under a variety of conditions.

Silkworm apolipophorin protein inhibits Staphylococcus aureus virulence

Silkworm hemolymph inhibits hemolysin production by Staphylococcus aureus. We purified a factor in the silkworm hemolymph responsible for this inhibitory activity. The final fraction with the greatest specific activity contained 220- and 74-kDa proteins. Determination of the N-terminal amino acid sequence revealed that the 220- and 74-kDa proteins were apolipophorin I and apolipophorin II, respectively, indicating that the factor was apolipophorin (ApoLp). The purified ApoLp fraction showed decreased expression of S. aureus hla encoding α-hemolysin, hlb encoding β-hemolysin, saeRS, and RNAIII, which activate the expression of these hemolysin genes. Injection of an anti-ApoLp antibody into the hemolymph increased the sensitivity of silkworms to the lethal effect of S. aureus. Hog gastric mucin, a mammalian homologue of ApoLp, decreased the expression of S. aureus hla and hlb. These findings suggest that ApoLp in the silkworm hemolymph inhibits S. aureus virulence and contributes to defense against S. aureus infection and that its activity is conserved in mammalian mucin.

Staphylococcus aureus regulates the expression and production of the staphylococcal superantigen-like secreted proteins in a Rot-dependent manner

Staphylococcus aureus overproduces a subset of immunomodulatory proteins known as the staphylococcal superantigen-like proteins (Ssls) under conditions of pore-mediated membrane stress. In this study we demonstrate that overproduction of Ssls during membrane stress is due to the impaired activation of the two-component module of the quorum-sensing accessory gene regulator (Agr) system. Agr-dependent repression of ssl expression is indirect and mediated by the transcription factor repressor of toxins (Rot). Surprisingly, we observed that Rot directly interacts with and activates the ssl promoters. The role of Agr and Rot as regulators of ssl expression was observed across several clinically relevant strains, suggesting that overproduction of immunomodulatory proteins benefits agr-defective strains. In support of this notion, we demonstrate that Ssls contribute to the residual virulence of S. aureus lacking agr in a murine model of systemic infection. Altogether, these results suggest that S. aureus compensates for the inactivation of Agr by producing immunomodulatory exoproteins that could protect the bacterium from host-mediated clearance.

Cell-directed-assembly: directing the formation of nano/bio interfaces and architectures with living cells

BACKGROUND

The desire to immobilize, encapsulate, or entrap viable cells for use in a variety of applications has been explored for decades. Traditionally, the approach is to immobilize cells to utilize a specific functionality of the cell in the system.

SCOPE OF REVIEW

This review describes our recent discovery that living cells can organize extended nanostructures and nano-objects to create a highly biocompatible nano//bio interface [1].

MAJOR CONCLUSIONS

We find that short chain phospholipids direct the formation of thin film silica mesophases during evaporation-induced self-assembly (EISA) [2], and that the introduction of cells alter the self-assembly pathway. Cells organize an ordered lipid-membrane that forms a coherent interface with the silica mesophase that is unique in that it withstands drying-yet it maintains accessibility to molecules introduced into the 3D silica host. Cell viability is preserved in the absence of buffer, making these constructs useful as standalone cell-based sensors. In response to hyperosmotic stress, the cells release water, creating a pH gradient which is maintained within the nanostructured host and serves to localize lipids, proteins, plasmids, lipidized nanocrystals, and other components at the cellular surface. This active organization of the bio/nano interface can be accomplished during ink-jet printing or selective wetting-processes allowing patterning of cellular arrays-and even spatially-defined genetic modification.

GENERAL SIGNIFICANCE

Recent advances in the understanding of nanotechnology and cell biology encourage the pursuit of more complex endeavors where the dynamic interactions of the cell and host material act symbiotically to obtain new, useful functions. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

Lipoproteomics: using mass spectrometry-based proteomics to explore the assembly, structure, and function of lipoproteins

Lipoproteins are centrally important in lipid transport, fuel metabolism, and cardiovascular disease. The prototypic lipoprotein has an outer shell of amphipathic lipids and proteins that solubilizes a hydrophobic lipid core. Lipoprotein-associated proteins have classically been viewed as structural elements and factors important in lipid metabolism. Recent mass spectrometric analyses reveal that the protein cargo of lipoproteins is much more diverse than previously appreciated, raising the possibility that lipoproteins play previously unsuspected roles in host defense mechanisms and inflammation. They further suggest that lipoprotein-associated proteins can identify humans at increased risk of cardiovascular disease. Here, we summarize recent developments in lipoproteomics, the proteomic analysis of lipoproteins. We also discuss the promises and challenges this powerful analytical strategy offers for expanding our understanding of the biology and structures of lipoproteins.

Serum proteomics signature of cystic fibrosis patients: a complementary 2-DE and LC-MS/MS approach

Complementary 2D-PAGE and 'shotgun' LC-MS/MS approaches were combined to identify medium and low-abundant proteins in sera of Cystic Fibrosis (CF) patients (mild or severe pulmonary disease) in comparison with healthy CF-carrier and non-CF carrier individuals aiming to gain deeper insights into the pathogenesis of this multifactorial genetic disease. 78 differentially expressed spots were identified from 2D-PAGE proteome profiling yielding 28 identifications and postulating the existence of post-translation modifications (PTM). The 'shotgun' approach highlighted altered levels of proteins actively involved in CF: abnormal tissue/airway remodeling, protease/antiprotease imbalance, innate immune dysfunction, chronic inflammation, nutritional imbalance and Pseudomonas aeruginosa colonization. Members of the apolipoproteins family (VDBP, ApoA-I, and ApoB) presented gradually lower expression from non-CF to CF-carrier individuals and from those to CF patients, results validated by an independent assay. The multifunctional enzyme NDKB was identified only in the CF group and independently validated by WB. Its functions account for ion sensor in epithelial cells, pancreatic secretion, neutrophil-mediated inflammation and energy production, highlighting its physiological significance in the context of CF. Complementary proteomics-based approaches are reliable tools to reveal pathways and circulating proteins actively involved in a heterogeneous disease such as CF.

Jamming bacterial communication: new approaches for the treatment of infectious diseases

The global rise of anti-microbial resistance, combined with the rapid rate of microbial evolution, and the slower development of novel antibiotics, underscores the urgent need for innovative therapeutics. We are facing a post-antibiotic era with a decreased armamentarium to combat infectious diseases. Development of novel drugs will rely on basic research aimed to increase our understanding of bacterial pathogenesis and the inter-cellular chemical signalling among bacterial cells. Such basic science, when combined with contemporary drug discovery technologies, may be translated into therapeutic applications to combat bacterial infections. In this review, we discuss many strategies aimed to interfere with bacterial cell-to-cell signalling via the quorum-sensing (QS) pathway to inhibit bacterial virulence and/or the development of microbial communities (known as biofilms), which are refractory to antibiotic treatment. QS antagonists should be viewed as blockers of pathogenicity rather than as anti-microbials and because QS is not involved in bacterial growth, inhibition of QS should not yield a strong selective pressure for development of resistance. QS inhibitors (QSIs) hold great expectations and we look forward to their application in fighting bacterial infections.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Relative contribution of Panton-Valentine leukocidin to PMN plasma membrane permeability and lysis caused by USA300 and USA400 culture supernatants

Panton-Valentine leukocidin (PVL) is a cytolytic toxin associated with severe community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections. However, the relative contribution of PVL to host cell lysis during CA-MRSA infection remains unknown. Here we investigated the relative contribution of PVL to human polymorphonuclear leukocyte (PMN) plasma membrane permeability and lysis in vitro by using culture supernatants from wild-type and isogenic lukS/F-PV negative (Deltapvl) USA300 and USA400 strains. Using S. aureus culture conditions that favor selective high production of PVL (CCY medium), there was on average more PMN plasma membrane permeability and cell lysis caused by supernatants derived from wild-type strains compared with those from Deltapvl strains. Unexpectedly, plasma membrane permeability did not necessarily correlate with ultimate cell lysis. Moreover, the level of pore formation caused by culture supernatants varied dramatically (e.g., range was 0.32-99.09% for wild-type USA300 supernatants at 30 min) and was not attributable to differences in PMN susceptibility to PVL among human blood donors. We conclude that PMN pore formation assays utilizing S. aureus culture supernatants have limited ability to estimate the relative contribution of PVL to pathogenesis (or cytolysis in vitro or in vivo), especially when assayed using culture media that promote selective high production of PVL.

Two-component signal transduction as potential drug targets in pathogenic bacteria

Gene clusters contributing to processes such as cell growth and pathogenicity are often controlled by two-component signal transduction systems (TCSs). Specific inhibitors against TCS systems work differently from conventional antibiotics, and developing them into new drugs that are effective against various drug-resistant bacteria may be possible. Furthermore, inhibitors of TCSs that control virulence factors may reduce virulence without killing the pathogenic bacteria. Previous TCS inhibitors targeting the kinase domain of the histidine kinase sensor suffered from poor selectivity. Recent TCS inhibitors, however, target the sensory domains of the sensors blocking the quorum sensing system, or target the essential response regulator. These new targets are introduced, together with several specific TCSs that have the potential to serve as effective drug targets.

Antimicrobial drug resistance

This chapter provides an overview of our current understanding of the mechanisms associated with the development of antimicrobial drug resistance, international differences in definitions of resistance, ongoing efforts to track shifts in drug susceptibility, and factors that can influence the selection of therapeutic intervention. The latter presents a matrix of complex variables that includes the mechanism of drug action, the pharmacokinetics (PK) of the antimicrobial agent in the targeted patient population, the pharmacodynamics (PD) of the bacterial response to the antimicrobial agent, the PK/PD relationship that will influence dose selection, and the integrity of the host immune system. Finally, the differences between bacterial tolerance and bacterial resistance are considered, and the potential for non-traditional anti-infective therapies is discussed.

Confinement-induced quorum sensing of individual Staphylococcus aureus bacteria

It is postulated that in addition to cell density, other factors such as the dimensions and diffusional characteristics of the environment could influence quorum sensing (QS) and induction of genetic reprogramming. Modeling studies predict that QS may operate at the level of a single cell, but, owing to experimental challenges, the potential benefits of QS by individual cells remain virtually unexplored. Here we report a physical system that mimics isolation of a bacterium, such as within an endosome or phagosome during infection, and maintains cell viability under conditions of complete chemical and physical isolation. For Staphylococcus aureus, we show that quorum sensing and genetic reprogramming can occur in a single isolated organism. Quorum sensing allows S. aureus to sense confinement and to activate virulence and metabolic pathways needed for survival. To demonstrate the benefit of confinement-induced quorum sensing to individuals, we showed that quorum-sensing bacteria have significantly greater viability over non-QS bacteria.

Microbial telesensing: probing the environment for friends, foes, and food

Bacterial-sensing circuits may be triggered by molecules originating from the environment (e.g., nutrients and chemoattractants). Bacteria also actively probe the environment for information by releasing molecular probes to measure conditions beyond the cell surface: a process known as telesensing. Perceiving the environment beyond is achieved by sensing environmentally induced changes in those probes, as occurs when a siderophore chelates an iron atom or a quorum-sensing signal is inactivated by a specific enzyme or adsorbent. This information, captured by chemical and physical changes induced in specifically produced molecules transiting through the environment, enables bacteria to mount a contextually appropriate response.