Functional analysis of the TCR binding domain of toxic shock syndrome toxin-1 predicts further diversity in MHC class II/superantigen/TCR ternary complexes

Superantigens (SAGs) aberrantly alter immune system function through simultaneous interaction with lateral surfaces of MHC class II molecules on APCs and with particular variable regions of the TCR beta-chain (Vbeta). To further define the interface between the bacterial SAG toxic shock syndrome toxin-1 (TSST-1) and the TCR, we performed alanine scanning mutagenesis within the putative TCR binding region of TSST-1 along the central alpha helix adjacent to the N-terminal alpha helix and the beta7-beta9 loop as well as with two universally conserved SAG residues (Leu(137) and Tyr(144) in TSST-1). Mutants were analyzed for multiple functional activities, and various residues appeared to play minor or insignificant roles in the TCR interaction. The locations of six residues (Gly(16), Trp(116), Glu(132), His(135), Gln(136), and Gln(139)), each individually critical for functional activity as well as direct interaction with the human TCR Vbeta2.1-chain, indicate that the interface occurs in a novel region of the SAG molecule. Based on these data, a model of the MHC/TSST-1/TCR ternary complex predicts similarities seen with other characterized SAGs, although the CDR3 loop of Vbeta2.1 is probably involved in direct SAG-TCR molecular interactions, possibly contributing to the TCR Vbeta specificity of TSST-1.     

Angiostrongylus cantonensis infection in molluscs in the municipality of S?o Gon?alo,a metropolitan area of Rio de Janeiro,Brazil: role of the invasive species Achatina fulica in parasite transmission dynamics

The aim of this study was to analyse the infection dynamics ofAngiostrongylus cantonensis in its possible intermediate hosts over two years in an urban area in the state of Rio de Janeiro where the presence ofA. cantonensis had been previously recorded in molluscs. Four of the seven mollusc species found in the study were exotic.Bradybaena similaris was the most abundant, followed byAchatina fulica, Streptaxis sp., Subulina octona, Bulimulus tenuissimus, Sarasinula linguaeformis and Leptinaria unilamellata. Only A. fulica and B. similaris were parasitised by A. cantonensis and both presented co-infection with other helminths. The prevalence of A. cantonensisin A. fulica was more than 50% throughout the study. There was an inverse correlation between the population size ofA. fulica and the prevalence of A. cantonensis and abundance of the latter was negatively related to rainfall. The overall prevalence of A. cantonensis in B. similariswas 24.6%. A. fulica was the most important intermediary host of A. cantonensis in the studied area andB. similaris was secondary in importance for A. cantonensis transmission dynamics.     

Non-Aqueous Glycerol Monolaurate Gel Exhibits Antibacterial and Anti-Biofilm Activity against Gram-Positive and Gram-Negative Pathogens

Background

Skin and surgical infections due to Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii are causes of patient morbidity and increased healthcare costs. These organisms grow planktonically and as biofilms, and many strains exhibit antibiotic resistance. This study examines the antibacterial and anti-biofilm activity of glycerol monolaurate (GML), as solubilized in a non-aqueous vehicle (5% GML Gel), as a novel, broadly-active topical antimicrobial. The FDA has designated GML as generally recognized as safe for human use, and the compound is commonly used in the cosmetic and food industries.

Methods

In vitro, bacterial strains in broths and biofilms were exposed to GML Gel, and effects on bacterial colony-forming units (CFUs) were assessed. In vivo,subcutaneous incisions were made in New Zealand white rabbits; the incisions were closed with four sutures. Bacterial strains were painted onto the incision sites, and then GML Gel or placebo was liberally applied to cover the sites completely. Rabbits were allowed to awaken and were examined for CFUs as a function of exposure time.

Results

In vitro, GML Gel was bactericidal for all broth culture and biofilm organisms in <1 hour and <4 hour, respectively; no CFUs were detected after the entire 24 h test period. In vivo, GML Gel inhibited bacterial growth in the surgical incision sites, compared to no growth inhibition in controls. GML Gel significantly reduced inflammation, as viewed by lack of redness in and below the incision sites.

Conclusions

Our findings suggest that 5% GML Gel is useful as a potent topical antibacterial and anti-inflammatory agent for prevention of infections.     

Modeling human arthritic diseases in nonhuman primates

Models of rheumatoid arthritis (RA) in laboratory animals are important tools for research into pathogenic mechanisms and the development of effective, safe therapies. Rodent models (rats and mice) have provided important information about the pathogenic mechanisms. However, the evolutionary distance between rodents and humans hampers the translation of scientific principles into effective therapies. The impact of the genetic distance between the species is especially seen with treatments based on biological molecules, which are usually species-specific. The outbred nature and the closer anatomical, genetic, microbiological, physiological, and immunological similarity of nonhuman primates to humans may help to bridge the wide gap between inbred rodent strain models and the heterogeneous RA patient population. Here we review clinical, immunological and pathological aspects of the rhesus monkey model of collagen-induced arthritis, which has emerged as a reproducible model of human RA in nonhuman primates.     

A toroid model for in vitro investigations of toxic shock syndrome toxin-1 production

Human behaviours and consumer products may affect vaginal microbial ecology, thereby influencing women's health. Relevant experimentation systems are needed to understand such possible links. Here, we describe the development of a practical semi-solid in vitro model to assess the effects of interactions between vaginal environment and the presence of tampons, on bacterial communities, including the production of toxic shock syndrome toxin-1 (TSST-1) by Staphylococcus aureus.     

Nucleotide sequence of the staphylococcal enterotoxin C1 gene and relatedness to other pyrogenic toxins

Summary The nucleotide sequence for the structural gene entC1 encoding staphylococcal enterotoxin C1 was determined. The gene contained 801 bp and coded for a protein of 266 amino acids. Of these, 27 comprised the signal peptide. Cleavage of the signal peptide resulted in a mature protein with 239 amino acids and a calculated molecular weight of 27496. The nucleotide sequence of entC1 shared considerable homology (74% and 59%, respectively) with genes encoding enterotoxin B and streptococcal pyrogenic exotoxin A. A similar degree of amino acid homology was observed after alignment of the respective proteins. Thus, certain regions of these three toxin molecules possess structural similarities that may be responsible for shared biological properties.     

Nonpurulent response to toxic shock syndrome toxin 1-producing Staphylococcus aureus. Relationship to toxin-stimulated production of tumor necrosis factor

Infection of surgical wounds with toxic shock syndrome toxin 1 (TSST-1)-producing Staphylococcus aureus does not usually elicit a purulent response from the host. Because S. aureus is normally a pyogenic pathogen, this phenomenon suggests that strains of staphylococci that produce the exotoxin are able to inhibit the migration of polymorphonuclear neutrophils (PMN) to sites of infection. We have considered that inhibition of leukocyte migration may be an effect of secreted TSST-1 and have studied direct and indirect effects of the exotoxin on migratory functions of PMN in vitro. Preincubation of PMN with TSST-1 produced no inhibition of random motility or FMLP- or C5a-stimulated chemotaxis under agarose. Supernatant fluids from mononuclear leukocytes incubated with TSST-1, however, were potently inhibitory for both PMN random and chemotactic migratory functions. The inhibitor of migration was identified as TNF based upon neutralization by anti-TNF antiserum and its presence in the culture supernatant fluids assayed in terms of cytotoxicity for murine TNF-sensitive L-929 cell line cells. Preincubation of PMN with recombinant human TNF also inhibited subsequent PMN random and chemotactic migratory functions. We propose that TSST-1 inhibits the mobilization of PMN to sites of infection by stimulation of monocyte/macrophage TNF production and suggest that TNF may also contribute to some other effects of toxic shock syndrome.     

Bacteriophage involvement in group A streptococcal pyrogenic exotoxin A production.

Lysogenic conversion has been suggested as a mechanism of control of group A streptococcal pyrogenic exotoxin type A production. Digestion of DNA from two converting bacteriophages, 3GL16 and T12, with a variety of restriction endonucleases yielded identical DNA fragments upon electrophoresis in agarose gels. Several known A toxin-positive strains that did not appear to produce converting phage upon induction were analyzed for toxin and phage DNA. Strains, including NY5, 594, and C203S, were shown by hybridization studies to carry the A toxin gene (speA) adjacent to chromosomally inserted phage fragments, homologous to phage T12 DNA, which may represent defective converting phages. The phage T12 att site mapped adjacent to speA. These data suggest that phage T12 acquired the A toxin gene from the bacterial genome. All streptococcal strains tested that were A toxin negative by Ouchterlony immunodiffusion failed to show any hybridization to speA-specific probes.