Purification and properties of staphylococcal delta hemolysin

In-Vitro Catalytic and Antibacterial Potential of Green Synthesized CuO Nanoparticles against Prevalent Multiple Drug Resistant Bovine Mastitogen Staphylococcus aureus

Nanoparticles prepared from bio-reduction agents are of keen interest to researchers around the globe due to their ability to mitigate the harmful effects of chemicals. In this regard, the present study aims to synthesize copper oxide nanoparticles (CuO NPs) by utilizing root extracts of ginger and garlic as reducing agents, followed by the characterization and evaluation of their antimicrobial properties against multiple drug resistant (MDR) S. aureus. In this study, UV-vis spectroscopy revealed a reduced degree of absorption with an increase in the extract amount present in CuO. The maximum absorbance for doped NPs was recorded around 250 nm accompanying redshift. X-ray diffraction analysis revealed the monoclinic crystal phase of the particles. The fabricated NPs exhibited spherical shapes with dense agglomeration when examined with FE-SEM and TEM. The crystallite size measured by using XRD was found to be within a range of 23.38-46.64 nm for ginger-doped CuO and 26-56 nm for garlic-doped CuO. Green synthesized NPs of ginger demonstrated higher bactericidal tendencies against MDR S. aureus. At minimum and maximum concentrations of ginger-doped CuO NPs, substantial inhibition areas for MDR S. aureus were (2.05-3.80 mm) and (3.15-5.65 mm), and they were measured as (1.1-3.55 mm) and (1.25-4.45 mm) for garlic-doped NPs. Conventionally available CuO and crude aqueous extract (CAE) of ginger and garlic roots reduced MB in 12, 21, and 38 min, respectively, in comparison with an efficient (100%) reduction of dye in 1 min and 15 s for ginger and garlic doped CuO NPs.

Cell-Penetrating Antimicrobial Peptides Derived from an Atypical Staphylococcal δ-Toxin

Revisiting underutilized classes of antibiotics is a pragmatic approach to the identification of alternative therapies for antimicrobial-resistant pathogens. To this end, we designed and screened a set of seven staphylococcal δ-toxin-inspired peptides (STIPs) for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, a pathogen-specific protease was leveraged to generate shorter peptides from these δ-toxin derivatives to expand the screen of putative antimicrobial peptides (AMPs) and to counterscreen against AMP inactivation. Remarkably, a 17-amino acid peptide based on the atypical δ-toxin sequence of Staphylococcus auricularis was discovered to possess an ability to kill MRSA and related pathogens. An alanine scan and series of rational substitutions improved AMP activity, and phenotypic assays characterized the STIPs’ ability to rapidly interact with and permeabilize the staphylococcal membrane without causing lysis on a commensurate timescale. Instead of rapid lysis, both l- and d-enantiomers of STIP3-29, an AMP with low micromolar activity, were observed to penetrate and accumulate within cells. Finally, we observed that STIP3-29 was capable of controlling MRSA infection in a three-dimensional skin infection model. Overall, the results suggest that this unconventional source of AMPs can provide promising candidates for further development as therapeutic agents.

IMPORTANCE The continued emergence and global distribution of infections caused by antimicrobial-resistant pathogens fuel our perpetual need for new or alternative therapies. Here, we present the discovery and initial characterization of bacterial cell-penetrating AMPs that were based on a family of virulence factors. In contrast to the multitude of AMPs that are sourced from animals, these potential therapeutic molecules have not undergone extensive selection for their antimicrobial properties and have proven to be amenable to activity-optimizing modifications. The staphylococcal toxin-inspired peptides described here represent a source of AMPs that can kill common opportunistic pathogens, such as MRSA, and have the potential to be improved for application in medicine.

Coarse-grained simulations of hemolytic peptide δ-lysin interacting with a POPC bilayer

δ-lysin, secreted by a Gram-positive bacterium Staphylococcus aureus, is a 26-residue membrane active peptide that shares many common features with antimicrobial peptides (AMPs). However, it possesses a few unique features that differentiate itself from typical AMPs. In particular, δ-lysin has zero net charge, even though it has many charged residues, and it preferentially lyses eukaryotic cells over bacterial cells. Here, we present the results of coarse-grained molecular dynamics simulations of δ-lysin interacting with a zwitterionic membrane over a wide range of peptide concentrations. When the peptides concentration is low, spontaneous dimerization of peptides is observed on the membrane surface, but deep insertion of peptides or pore formation was not observed. However, the calculated free energy of peptide insertion suggests that a small fraction of peptides is likely to be present inside the membrane at the peptide concentrations typically seen in dye efflux experiments. When the simulations with multiple peptides are carried out with a single pre-inserted transmembrane peptide, spontaneous pore formation occurs with a peptide-to-lipid ratio (P/L) as low as P/L=1:42. Inter-peptide salt bridges among the transmembrane peptides seem to play a role in creating compact pores with very low level of hydration. More importantly, the transmembrane peptides making up the pore are constantly pushed to the opposite side of the membrane when the mass imbalance between the two sides of membrane is significant. Thus, the pore is very dynamic, allowing multiple peptides to translocate across the membrane simultaneously.

Branched phospholipids render lipid vesicles more susceptible to membrane-active peptides

Iso- and anteiso-branched lipids are abundant in the cytoplasmic membranes of bacteria. Their function is assumed to be similar to that of unsaturated lipids in other organisms - to maintain the membrane in a fluid state. However, the presence of terminally branched membrane lipids is likely to impact other membrane properties as well. For instance, lipid acyl chain structure has been shown to influence the activity of antimicrobial peptides. Moreover, the development of resistance to antimicrobial agents in Staphylococcus aureus is accompanied by a shift in the fatty acid composition toward a higher fraction of anteiso-branched lipids. Little is known about how branched lipids and the location of the branch point affect the activity of membrane-active peptides. We hypothesized that bilayers containing lipids with low phase transition temperatures would tend to exclude peptides and be less susceptible to peptide-induced perturbation than those made from higher temperature melting lipids. To test this hypothesis, we synthesized a series of asymmetric phospholipids that only differ in the type of fatty acid esterified at the sn-2 position of the lipid glycerol backbone. We tested the influence of acyl chain structure on peptide activity by measuring the kinetics of release from dye-encapsulated lipid vesicles made from these synthetic lipids. The results were compared to those obtained using vesicles made from S. aureus and Staphylococcus sciuri membrane lipid extracts. Anteiso-branched phospholipids, which melt at very low temperatures, produced lipid vesicles that were only slightly less susceptible to peptide-induced dye release than those made from the iso-branched isomer. However, liposomes made from bacterial phospholipid extracts were generally much more resistant to peptide-induced perturbation than those made from any of the synthetic lipids. The results suggest that the increase in the fraction of anteiso-branched fatty acids in antibiotic-resistant strains of S. aureus is unlikely to be the sole factor responsible for the observed increased antibiotic resistance. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Pathogenesis of Staphylococcus aureus abscesses

Staphylococcus aureus causes many types of human infections and syndromes-most notably skin and soft tissue infections. Abscesses are a frequent manifestation of S. aureus skin and soft tissue infections and are formed, in part, to contain the nidus of infection. Polymorphonuclear leukocytes (neutrophils) are the primary cellular host defense against S. aureus infections and a major component of S. aureus abscesses. These host cells contain and produce many antimicrobial agents that are effective at killing bacteria, but can also cause non-specific damage to host tissues and contribute to the formation of abscesses. By comparison, S. aureus produces several molecules that also contribute to the formation of abscesses. Such molecules include those that recruit neutrophils, cause host cell lysis, and are involved in the formation of the fibrin capsule surrounding the abscess. Herein, we review our current knowledge of the mechanisms and processes underlying the formation of S. aureus abscesses, including the involvement of polymorphonuclear leukocytes, and provide a brief overview of therapeutic approaches.

Emerging functions for the Staphylococcus aureus RNome

Staphylococcus aureus is a leading pathogen for animals and humans, not only being one of the most frequently isolated bacteria in hospital-associated infections but also causing diseases in the community. To coordinate the expression of its numerous virulence genes for growth and survival, S. aureus uses various signalling pathways that include two-component regulatory systems, transcription factors, and also around 250 regulatory RNAs. Biological roles have only been determined for a handful of these sRNAs, including cis, trans, and cis-trans acting RNAs, some internally encoding small, functional peptides and others possessing dual or multiple functions. Here we put forward an inventory of these fascinating sRNAs; the proteins involved in their activities; and those involved in stress response, metabolisms, and virulence.

Cytoplasmic replication of Staphylococcus aureus upon phagosomal escape triggered by phenol-soluble modulin α

Staphylococcus aureus is a Gram-positive human pathogen that is readily internalized by professional phagocytes such as macrophages and neutrophils but also by non-professional phagocytes such as epithelial or endothelial cells. Intracellular bacteria have been proposed to play a role in evasion of the innate immune system and may also lead to dissemination within migrating phagocytes. Further, S. aureus efficiently lyses host cells with a battery of cytolytic toxins. Recently, phenol-soluble modulins (PSM) have been identified to comprise a genus-specific family of cytolytic peptides. Of these the PSMα peptides have been implicated in killing polymorphonuclear leucocytes after phagocytosis. We questioned if the peptides were active in destroying endosomal membranes to avoid lysosomal killing of the pathogen and monitored integrity of infected host cell endosomes by measuring the acidity of the intracellular bacterial microenvironment via flow cytometry and by a reporter recruitment technique. Isogenic mutants of the methicillin-resistant S. aureus (MRSA) strains USA300 LAC, USA400 MW2 as well as the strongly cytolytic methicillin-sensitive strain 6850 were compared with their respective wild type strains. In all three genetic backgrounds, PSMα mutants were unable to escape from phagosomes in non-professional (293, HeLa, EAhy.926) and professional phagocytes (THP-1), whereas mutants in PSMβ and δ-toxin as well as β-toxin, phosphatidyl inositol-dependent phospholipase C and Panton Valentine leucotoxin escaped with efficiencies of the parental strains. S. aureus replicated intracellularly only in presence of a functional PSMα operon thereby illustrating that bacteria grow in the host cell cytoplasm upon phagosomal escape.

Intracellular Staphylococcus aureus: live-in and let die

Staphylococcus aureus uses a plethora of virulence factors to accommodate a diversity of niches in its human host. Aside from the classical manifestations of S. aureus-induced diseases, the pathogen also invades and survives within mammalian host cells.The survival strategies of the pathogen are as diverse as strains or host cell types used. S. aureus is able to replicate in the phagosome or freely in the cytoplasm of its host cells. It escapes the phagosome of professional and non-professional phagocytes, subverts autophagy, induces cell death mechanisms such as apoptosis and pyronecrosis, and even can induce anti-apoptotic programs in phagocytes. The focus of this review is to present a guide to recent research outlining the variety of intracellular fates of S. aureus.

Inhibition of colony-spreading activity of Staphylococcus aureus by secretion of δ-hemolysin

Staphylococcus aureus spreads on the surface of soft agar, a phenomenon we termed "colony spreading." Here, we found that S. aureus culture supernatant inhibited colony spreading. We purified δ-hemolysin (Hld, δ-toxin), a major protein secreted from S. aureus, as a compound that inhibits colony spreading. The culture supernatants of hld-disrupted mutants had 30-fold lower colony-spreading inhibitory activity than those of the parent strain. Furthermore, hld-disrupted mutants had higher colony-spreading ability than the parent strain. These results suggest that S. aureus negatively regulates colony spreading by secreting δ-hemolysin.

Staphylococcus aureus hemolysins, bi-component leukocidins, and cytolytic peptides: a redundant arsenal of membrane-damaging virulence factors?

One key aspect of the virulence of Staphylococcus aureus lies in its ability to target the host cell membrane with a large number of membrane-damaging toxins and peptides. In this review, we describe the hemolysins, the bi-component leukocidins (which include the Panton Valentine leukocidin, LukAB/GH, and LukED), and the cytolytic peptides (phenol soluble modulins). While at first glance, all of these factors might appear redundant, it is now clear that some of these factors play specific roles in certain S. aureus life stages and diseases or target specific cell types or species. In this review, we present an update of the literature on toxin receptors and their cell type and species specificities. Furthermore, we review epidemiological studies and animal models illustrating the role of these membrane-damaging factors in various diseases. Finally, we emphasize the interplay of these factors with the host immune system and highlight all their non-lytic functions.

Immunopathogenesis of Staphylococcus aureus pulmonary infection

Staphylococcus aureus is a common human pathogen highly evolved as both a component of the commensal flora and as a major cause of invasive infection. Severe respiratory infection due to staphylococci has been increasing due to the prevalence of more virulent USA300 CA-MRSA strains in the general population. The ability of S. aureus to adapt to the milieu of the respiratory tract has facilitated its emergence as a respiratory pathogen. Its metabolic versatility, the ability to scavenge iron, coordinate gene expression, and the horizontal acquisition of useful genetic elements have all contributed to its success as a component of the respiratory flora, in hospitalized patients, as a complication of influenza and in normal hosts. The expression of surface adhesins facilitates its persistence in the airways. In addition, the highly sophisticated interactions of the multiple S. aureus virulence factors, particularly the α-hemolysin and protein A, with diverse immune effectors in the lung such as ADAM10, TNFR1, EGFR, immunoglobulin, and complement all contribute to the pathogenesis of staphylococcal pneumonia.

What determines the activity of antimicrobial and cytolytic peptides in model membranes

We previously proposed three hypotheses relating the mechanism of antimicrobial and cytolytic peptides in model membranes to the Gibbs free energies of binding and insertion into the membrane [Almeida, P. F., and Pokorny, A. (2009) Biochemistry 48, 8083-8093]. Two sets of peptides were designed to test those hypotheses, by mutating of the sequences of δ-lysin, cecropin A, and magainin 2. Peptide binding and activity were measured on phosphatidylcholine membranes. In the first set, the peptide charge was changed by mutating basic to acidic residues or vice versa, but the amino acid sequence was not altered much otherwise. The type of dye release changed from graded to all-or-none according to prediction. However, location of charged residues in the sequence with the correct spacing to form salt bridges failed to improve binding. In the second set, the charged and other key residues were kept in the same positions, whereas most of the sequence was significantly but conservatively simplified, maintaining the same hydrophobicity and amphipathicity. This set behaved completely different from predicted. The type of release, which was expected to be maintained, changed dramatically from all-or-none to graded in the mutants of cecropin and magainin. Finally, contrary to the hypotheses, the results indicate that the Gibbs energy of binding to the membrane, not the Gibbs energy of insertion, is the primary determinant of peptide activity.

Expression of δ-toxin by Staphylococcus aureus mediates escape from phago-endosomes of human epithelial and endothelial cells in the presence of β-toxin

Staphylococcus aureus is able to invade non-professional phagocytes by interaction of staphylococcal adhesins with extracellular proteins of mammalian cells and eventually resides in acidified phago-endosomes. Some staphylococcal strains have been shown to subsequently escape from this compartment. A functional agr quorum-sensing system is needed for phagosomal escape. However, the nature of this agr dependency as well as the toxins involved in disruption of the phagosomal membrane are unknown. Using a novel technique to detect vesicular escape of S. aureus, we identified staphylococcal virulence factors involved in phagosomal escape. Here we show that a synergistic activity of the cytolytic peptide, staphylococcal δ-toxin and the sphingomyelinase β-toxin enable the phagosomal escape of staphylococci in human epithelial as well as in endothelial cells. The agr dependency of this process can be directly explained by the location of the structural gene for δ-toxin within the agr effector RNAIII.

Purification and characterization of a novel delta-lysin variant that inhibits Staphylococcus aureus and has limited hemolytic activity

Delta-lysins (DL) that are produced by various species of staphylococci are not widely known for their antimicrobial activity. We have purified and characterized a novel DL variant, E229DL and examined its spectrum of inhibitory activity. The biological activity of E229DL, produced by Staphylococcus epidermidis strain E229, shows relatively broad-spectrum activity against Gram-positive pathogens, including representatives of MRSA and epidemic MRSA type 15. E229DL was purified to homogeneity from 95% acidified-methanol extracts of cell cultures by using a series of reversed-phase chromatographic separations. The fully processed form of E229DL is a 25-amino-acid peptide with a predicted mass of 2841.4 Da, but the purified biologically active molecule appears to be N-formylated (mass 2867.33 Da). The DL gene (hld) resembles that of other types of DL, but differs in five codons with hld in Staphylococcus aureus (26 residues) and one codon with the closest homolog, the hld-II in S. warneri (25 residues). The characterization of E229DL showed that its activity is stable in agar exposed to high temperatures (80 degrees C/45 min). In addition, biological testing of the native and synthetic peptides against a range of human and animal erythrocytes and Vero cells indicated that E229DL is an antibacterial agent with no detectable cytopathic effects at concentrations equivalent to the minimum inhibitory concentration for EMRSA15-A208. Initial investigation of the mode of action of E229DL indicated that it is rapidly lytic for target cells. This is the first description of a native form of DL having only limited cytotoxic activity for eukaryotic cells at concentrations that are inhibitory to staphylococci.

Disruption of bacterial protoplasts and spheroplasts by staphylococcal delta hemolysin

Fractionation of highly purified staphylococcal delta hemolysin by sucrose density gradient centrifugation, Sephadex G-150 and Bio-Gel A-5m gel filtration, carboxymethyl cellulose chromatography, and isoelectric focusing failed to separate the hemolytic, protoplast-lysing, and spheroplast-lysing activities of the preparation. The activities were reduced to a similar extent when delta hemolysin was treated with any of several phospholipids. The same was true when serum or proteolytic enzymes were used as inactivating agents. Cholesterol had no effect. The activities resisted heating at 80 C for 1 hr and were stable for at least 7 days at 5 C in 0.1 n sodium hydroxide, 0.1 n acetic acid, 6 m guanidine hydrochloride, 8 m urea, and 0.1% sodium lauryl sulfate.

Detergent-like activity and alpha-helical structure of warnericin RK, an anti-Legionella peptide

Warnericin RK is the first antimicrobial peptide known to be active against Legionella pneumophila, a pathogen bacterium that is responsible for severe pneumonia. Strikingly, this peptide displays a very narrow range of antimicrobial activity, almost limited to the Legionella genus, and a hemolytic activity. A similar activity has been described for delta-lysin, a well-known hemolytic peptide of Staphylococci that has not been described as antimicrobial. In this study we aimed to understand the mode of action of warnericin RK and to explain its particular target specificity. We found that warnericin RK permeabilizes artificial membranes in a voltage-independent manner. Osmotic protection experiments on erythrocytes showed that warnericin RK does not form well-defined pores, suggesting a detergent-like mode of action, as previously described for delta-lysin at high concentrations. Warnericin RK also permeabilized Legionella cells, and these cells displayed a high sensitivity to detergents. Depending on the detergent used, Legionella was from 10- to 1000-fold more sensitive than the other bacteria tested. Finally, the structure of warnericin RK was investigated by means of circular dichroism and NMR spectroscopy. The peptide adopted an amphiphilic alpha-helical structure, consistent with the proposed mode of action. We conclude that the specificity of warnericin RK toward Legionella results from both the detergent-like mode of action of the peptide and the high sensitivity of these bacteria to detergents.

Mechanisms of antimicrobial, cytolytic, and cell-penetrating peptides: from kinetics to thermodynamics

The mechanisms of six different antimicrobial, cytolytic, and cell-penetrating peptides, including some of their variants, are discussed and compared. The specificity of these polypeptides varies; however, they all form amphipathic alpha-helices when bound to membranes, and there are no striking differences in their sequences. We have examined the thermodynamics and kinetics of their interaction with phospholipid vesicles, namely, binding and peptide-induced dye efflux. The thermodynamics of binding calculated using the Wimley-White interfacial hydrophobicity scale are in good agreement with the values derived from experiment. The generally accepted view that binding affinity determines functional specificity is also supported by experiments in model membranes. We now propose the hypothesis that it is the thermodynamics of the insertion of the peptide into the membrane, from a surface-bound state, that determine the mechanism.

delta-hemolysin, an update on a membrane-interacting peptide

delta-hemolysin is a hemolytic peptide produced by Staphylococcus, and it has been studied for nearly 50 years. Therefore, it has become a model in the study of peptides interacting with membranes. In this review, we report some recent findings and compare them with previous works. delta-hemolysin is a 26 amino acid peptide, somewhat hydrophobic and presenting a zero net charge. Study of its structure has shown that delta-hemolysin is alpha-helical and amphipathic, such as many antimicrobial peptides (e.g. magainin and melittin). However, delta-hemolysin had not displayed any reported antimicrobial activity until a recent publication showed its high potency against Legionella. Its mode of action is based on direct interaction with target membranes. In accordance with its concentration, delta-hemolysin may slightly perturb a membrane or lead to cell lysis. Peptide charge plays an important role in its interaction with membranes, as is shown in the study of peptide variants. Some positively charged variants become highly hemolytic and even active against Escherichia coli and Staphylococcus aureus. Finally, it has recently been demonstrated that peptide preferentially binds to lipid-disordered domains. It has been postulated that as a result, enrichment in lipid-ordered domains might increase peptide concentration in lipid-disordered domains and thereby improve its activity.

The activity of the amphipathic peptide delta-lysin correlates with phospholipid acyl chain structure and bilayer elastic properties

Release of lipid vesicle content induced by the amphipathic peptide delta-lysin was investigated as a function of lipid acyl chain length and degree of unsaturation for a series of phosphatidylcholines. Dye efflux and peptide binding were examined for three homologous lipid series: di-monounsaturated, di-polyunsaturated, and asymmetric phosphatidylcholines, with one saturated and one monounsaturated acyl chain. Except for the third series, peptide activity correlated with the first moment of the lateral pressure profile, which is a function of lipid acyl chain structure. In vesicles composed of asymmetric phosphatidylcholines, peptide binding and dye efflux are enhanced compared to symmetric, unsaturated lipids with similar pressure profiles. We attribute this to the entropically more favorable interaction of delta-lysin with partially saturated phospholipids. We find that lipid acyl chain structure has a major impact on the activity of delta-lysin and is likely to be an important factor contributing to the target specificity of amphipathic peptides.

Characterization of anti-Legionella activity of warnericin RK and delta-lysin I from Staphylococcus warneri

Legionella pneumophila, the causative agent of Legionnaires' disease, is a waterborne bacteria. It can multiply in man-made water systems and infect people who inhale contaminated droplets. We have previously reported a Staphylococcus warneri strain that display an anti-Legionella activity. In this work, we characterized three anti-Legionella peptides that are produced by S. warneri. One peptide, warnericin RK, is original, while the two others are delta-lysin I and delta-lysin II, whose genes were previously described. Due to high sequence similarity of the two delta-lysins, further characterization was performed only on delta-lysin I. Warnericin RK and delta-lysin I displayed the same antibacterial spectrum, which is almost restricted to the Legionella genus. Also, both peptides have a hemolytic activity. These results led to the hypothesis that warnericin RK and delta-lysin I share a similar mode of action, and that Legionella should have a specific feature that may explain the high specificity of these antibacterial peptides.

Isolation and characterization of a haemolysin from Trichophyton mentagrophytes

Haemolytic activities of Trichophyton (T.) mentagrophytes were detected and characterized by qualitative and quantitative assays. On Columbia agar supplemented with blood from horses, cattle or sheep, T. mentagrophytes expressed a strong zone of complete haemolysis. No haemolytic activities could be detected in the closely related T. verrucosum var. ochraceum. The same results were obtained after cultivation of the fungi on sterile cellulose acetate filters placed on the surface on Columbia blood agar. After removal of the filter, complete haemolysis was detected below the colony of T. mentagrophytes. A soluble haemolysin from culture supernatant of this strain was isolated and partially purified. Specific haemolytic activity per mg protein was enriched 2.6-fold in filtrate F(1), a fraction obtained as filtrate after filtration through 3kDa cut-off membranes. The partially purified haemolysin was neither affected by proteinase K treatment, nor by high and low temperatures, suggesting that it represents a small peptide haemolysin. Accordingly, in a commercial enzymatic activity test only the crude culture filtrate, but none of the subsequent purification fractions showed reactivity. Evaluation of the specificity of the haemolysin using erythrocytes from different mammalian species revealed that sensitivity was highest to those of equines, followed by erythrocytes from sheep, cattle, swine, dogs and humans. None of the erythrocytes was lysed by filtrate F(1) from T. verrucosum var. ochraceum. Furthermore, different eukaryotic cell lines from different species were tested in their sensitivity to cytolytic activities of the haemolysin, but no membrane damage could be detected.

Surface properties of membrane systems. Transport of staphylococcal delta-toxin from aqueous to membrane phase

Hemolytic delta-toxin from Staphylococcus aureus was soluble in either water, methanol or chloroform/methanol (2 : 1, v/v). The toxin spread readily from distilled water into films with pressures (pi) of 10 dynes/cm on water and 30 dynes/cm on 6 M urea; from chloroform/methanol it produced 40 dynes/cm pressure on distilled water. The toxin adsorbed barely from water (pi = 1 dyne/ cm) but it did rapidly from 6 M urea (pi = 35 dynes/cm). The protein films had unusually high surface potentials, which increased with the film pressure and decreased with increasing both pH and urea concentration in the aqueous phase. The fluorescence of 1-aniline 8-naphthalene sulfonate with delta-toxin was much greater than that with RNAase and dipalmitoyl phosphatidylcholine itself, indicating probably a marked lipid-binding character of the toxin. By circular dichroism the alpha-helix content of delta-toxin was 42% in water, 45% in methanol, 24% in 6 M urea. Infrared spectroscopy showed predominant alpha-helix in both 2H2O and deuterated chloroform/methanol as well as in films spread from either solvent on 2H2O. In spreading from 6 M [2H]urea, in which the major infrared absorption was that of [2H]urea with peaks at 1600 and 1480 cm(-1), the delta-toxin film showed prevalently non-alpha-helix structures with major peak intensities at 1633 cm(-1) > 1680 cm(-1), indicating the appearance of new beta-aggregated and beta-antiparallel pleated sheet structures in the film. The data prove that (1) high pressure protein films can consist of alpha-helix as well as non-alpha-helix structures and, differently from another cytolytic protein, melittin, delta-toxin does not resume the alpha-helix conformation in going into the film phase from the extended chain in 6 M urea; (2) conformational changes are important in the transport of proteins from aqueous to lipid or membrane phase; (3) delta-toxin is by far more versatile in structural dynamics and more surface active than alpha-toxin.

Conformation and activity of delta-lysin and its analogs

Delta-Lysin is a 26-residue hemolytic peptide secreted by Staphylococcus aureus. Unlike the bee venom peptide melittin, delta-lysin does not exhibit antibacterial activity. We have synthesized delta-lysin and several analogs wherein the N-terminal residues of the toxin were sequentially deleted. The toxin has three aspartic acids, four lysines and no prolines. Analogs were also generated in which all the aspartic acids were replaced with lysines. A proline residue was introduced in the native sequences as well as in the analogs where aspartic acids were replaced with lysines. We observed that 20- and 22-residue peptides corresponding to residues 7-26 and 5-26 of delta-lysin, respectively, had greater hemolytic activity than the parent peptide. These shorter peptides, unlike delta-lysin, did not self-associate to adopt alpha-helical conformation in water, at lytic concentrations. Introduction of proline or substitution of aspartic acids by lysines resulted in loss in propensity to adopt helical conformation in water. When proline was introduced in the peptides corresponding to the native toxin sequence, loss of hemolytic activity was observed. Substitution of all the aspartic acids with lysines resulted in enhanced hemolytic activity in all the analogs. However, when both proline and aspartic acid to lysine changes were made, only antibacterial activity was observed in the shorter peptides. Our investigations on delta-lysin and its analogs provide insights into the positioning of anionic, cationic residues and proline in determining hemolytic and antibacterial activities.

Exotoxins of Staphylococcus aureus

This article reviews the literature regarding the structure and function of two types of exotoxins expressed by Staphylococcus aureus, pyrogenic toxin superantigens (PTSAgs) and hemolysins. The molecular basis of PTSAg toxicity is presented in the context of two diseases known to be caused by these exotoxins: toxic shock syndrome and staphylococcal food poisoning. The family of staphylococcal PTSAgs presently includes toxic shock syndrome toxin-1 (TSST-1) and most of the staphylococcal enterotoxins (SEs) (SEA, SEB, SEC, SED, SEE, SEG, and SEH). As the name implies, the PTSAgs are multifunctional proteins that invariably exhibit lethal activity, pyrogenicity, superantigenicity, and the capacity to induce lethal hypersensitivity to endotoxin. Other properties exhibited by one or more staphylococcal PTSAgs include emetic activity (SEs) and penetration across mucosal barriers (TSST-1). A detailed review of the molecular mechanisms underlying the toxicity of the staphylococcal hemolysins is also presented.

Exotoxins of Staphylococcus aureus

This article reviews the literature regarding the structure and function of two types of exotoxins expressed by Staphylococcus aureus, pyrogenic toxin superantigens (PTSAgs) and hemolysins. The molecular basis of PTSAg toxicity is presented in the context of two diseases known to be caused by these exotoxins: toxic shock syndrome and staphylococcal food poisoning. The family of staphylococcal PTSAgs presently includes toxic shock syndrome toxin-1 (TSST-1) and most of the staphylococcal enterotoxins (SEs) (SEA, SEB, SEC, SED, SEE, SEG, and SEH). As the name implies, the PTSAgs are multifunctional proteins that invariably exhibit lethal activity, pyrogenicity, superantigenicity, and the capacity to induce lethal hypersensitivity to endotoxin. Other properties exhibited by one or more staphylococcal PTSAgs include emetic activity (SEs) and penetration across mucosal barriers (TSST-1). A detailed review of the molecular mechanisms underlying the toxicity of the staphylococcal hemolysins is also presented.

Regulation of agr-dependent virulence genes in Staphylococcus aureus by RNAIII from coagulase-negative staphylococci

Many of the genes coding for extracellular toxins, enzymes, and cell surface proteins in Staphylococcus aureus are regulated by a 510-nucleotide (nt) RNA molecule, RNAIII. Transcription of genes encoding secreted toxins and enzymes, including hla (alpha-toxin), saeB (enterotoxin B), tst (toxic shock syndrome toxin 1), and ssp (serine protease), is stimulated, while transcription of genes encoding cell surface proteins, like spa (protein A) and fnb (fibronectin binding proteins), is repressed. Besides being a regulator, RNAIII is also an mRNA coding for staphylococcal delta-lysin. We have identified RNAIII homologs in three different coagulase-negative staphylococci (CoNS), i.e., Staphylococcus epidermidis, Staphylococcus simulans, and Staphylococcus warneri. RNAIII from these CoNS turned out to be very similar to that of S. aureus and contained open reading frames encoding delta-lysin homologs. Though a number of big insertions and/or deletions have occurred, mainly in the 5' half of the molecules, the sequences show a high degree of identity, especially in the first 50 and last 150 nt. The CoNS RNAIII had the ability to completely repress transcription of protein A in an RNAIII-deficient S. aureus mutant and the ability to stimulate transcription of the alpha-toxin and serine protease genes. However, the stimulatory effect was impaired compared to that of S. aureus RNAIII, suggesting that these regulatory functions are independent. By creating S. epidermidis-S. aureus RNAIII hybrids, we could also show that both the 5' and 3' halves of the RNAIII molecule are involved in the transcriptional regulation of alpha-toxin and serine protease mRNAs in S. aureus.

Influence of staphylococcal delta-toxin on the phosphatidylcholine headgroup as observed using 2H-NMR

The interaction of the 8-toxin peptide isolated from Staphylococcus aureus with the headgroup region of lipid bilayer membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was investigated using deuterium (2H) and phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy. At relatively low peptide/lipid ratios (P/L < 0.10), all 2H- and 31P-NMR spectral lineshapes at 25 degrees C were indicative of a single population of liquid-crystalline lipids in a bilayer arrangement. At these P/L ratios, delta-toxin had only marginal effects on the size of the quadrupole splitting measured from POPC labelled at either the alpha-methylene (POPC-alpha-d2) or the beta-methylene segment (POPC-beta-d2) of the choline headgroup and, similarly small effects on the magnitude of the chemical shift anisotropy (CSA) of the 31P-NMR spectrum. With increasing amounts of delta-toxin (0.10 < P/L < 0.15) the size of the 2H quadrupole splitting from POPC-alpha-d2, as well as the magnitude of the 31P-CSA, decreased progressively and rapidly. The quadrupole splitting from POPC-beta-d2, however, remained relatively unaffected. At yet higher levels of delta-toxin (P/L > 0.15), all 2H- and 31P-NMR spectra indicated the presence of multiple lipid populations experiencing varying degrees of increased conformational disordering. The spectral lineshapes of these apparently nonbilayer spectral components reverted to bilayer-type lineshapes upon lowering the measuring temperature to 5 degrees C. At the utmost highest level of delta-toxin measured here (P/L = 0.20), all 2H- and 31P-NMR spectra consisted of a single, broad, apparently nonbilayer-type component, indicative of hindered but virtual isotropic motional averaging of the POPC headgroups. In this case no reversion to bilayer-type spectra could be obtained by decreasing the temperature. We could obtain no evidence that the conformation of the choline headgroup of POPC was responding to any specific influence of delta-toxin on bilayer surface electrostatics.

The amphiphilic alpha-helix concept. Consequences on the structure of staphylococcal delta-toxin in solution and bound to lipids

Staphylococcal delta-toxin, a synthetic analogue and a fragment were studied in order to determine their structure in solution and bound in lipids. In solution, a self-association process is observed. Analytical ultracentrifuge and quasi-elastic light-scattering experiments suggest an isodesmic aggregation in the high concentration domain above 2 microM up to very large asymmetrical species. Decreasing concentrations below 2 microM of delta-toxin and the analogue allows dissociation, probably into monomers. The self-associated species are essentially alpha-helical (70%) with buried and highly immobilized Trp either at position 15 for natural delta-toxin or 16 for the analogue. At the lowest concentration studied, the alpha-helix content severely decreases down to 35% while Trp fluorescence shows that these residues are exposed to buffer. The fragment 11-26 is always monomeric and structureless. From all the data, a structural model of aggregated species is proposed with stacked antiparallel amphipathic rods. When bound to lipids, whatever their initial structure in solution, 26-residue long peptides mainly adopt an alpha-helix conformation (80%) while fragment 11-26 exhibits about 50% alpha-helix. The lipid-peptide interactions were quantitatively analysed. For fragment 11-26, a single-step mechanism fits the spectroscopic changes and defines a single monomeric bound structure. On the other hand, for the 26-residue-long analogue, multiple-step processes must occur. The data were analysed with a partition of tetramers into lipids followed by a partial dissociation. Finally, the affinity of fragment 11-26 severely decreases from micelles to fluid and gel-state bilayers. The partition coefficient of the delta-toxin analogue is higher than those of other more apolar peptides, such as melittin and alamethicin, correlating with Eisenberg's hydrophobic moments. It is therefore proposed that delta-toxin probably lies parallel to the surface, only penetrating weakly in lipids, depending on their packing.

Effect of staphylococcal delta-toxin and bee venom peptide melittin on leukotriene induction and metabolism of human polymorphonuclear granulocytes

The abilities of delta-toxin from Staphylococcus aureus and melittin to induce and modulate the generation of leukotriene from human polymorphonuclear granulocytes (PMNs) were studied. Stimulation of PMNs with melittin (10 micrograms) induced leukotriene formation, whereas stimulation with delta-toxin did not. Preincubation of the PMNs with delta-toxin modulated the subsequent generation of leukotriene from PMNs induced by Ca ionophore A23187 or opsonized zymosan. The generation of leukotriene B4 (LTB4), induced by the Ca ionophore A23187, was increased when the PMNs were preincubated with delta-toxin for 5 min. When opsonized zymosan was used as a secondary stimulus to activate the delta-toxin-pretreated PMNs, LTB4 generation decreased. In contrast, melittin showed no significant modulatory effect on the generation of leukotriene from PMNs. In addition, preincubation of PMNs with delta-toxin inhibited the conversion of LTB4 to omega-oxidation products. Our data suggest that peptides with similar structures, e.g., delta-toxin and melittin, induce and modify leukotriene generation in different manners.

Comparative study of hemolytic substances produced by coagulase-negative Staphylococcus strains

Hemolytic substances H7, H62, and E56, produced by Staphylococcus haemolyticus 7 and 62 and S. epidermidis 56, respectively, were purified. H7 and H62 are probably similar on the basis of their isoelectric focusing profiles in 8 M urea and complete immunological identity as revealed by immunodiffusion with rabbit anti-H7 and anti-E56 sera. For E56, we observed seven bands instead of three in isoelectric focusing and only partial immunological identity with H7 and H62. However, H7 and E56 were similar with regard to the following characteristics: hemolytic spectra against different erythrocytes, kinetics of erythrocyte lysis, heat stability, and inhibition by phosphatidylcholine. E56 was not active at a temperature lower than or equal to 25 degrees C, and its activity increased more rapidly with increased temperature compared with H7. For both substances, the complexes obtained by molecular filtration on Ultrogel AcA54 and the purified peptides by reverse-phase high-pressure liquid chromatography showed some hemolytic activity. These results suggest that a particular association or the presence of a given peptide could enhance the activity.

Delta-haemolysin from Staphylococcus aureus and model membranes. A solid-state 2H-NMR and 31P-NMR study

Solid-state 2H NMR and 31P NMR of 2H-enriched chains and polar head groups, respectively, of dipalmitoylglycerophosphatidylcholine/water dispersions were undertaken to investigate the action of delta-haemolysin from Staphylococcus aureus on biomembranes. When the lipid/toxin molar ratio, Ri, is greater than or equal to 10, the gel-phase 2H powder patterns and the temperature of the gel-fluid phase transition, tc, are unchanged by the presence of the toxin whereas the 31P powder spectra of polar head groups are perturbed. At t greater than tc, a detailed analysis of methylene ordering indicates that delta-haemolysin orders the lipid chains near tc and disorders them for t much greater than tc. These findings are interpreted in terms of peptide location with regard to the membrane and suggest that the position of the toxin depends on the temperature relative to tc. Experiments carried out at Ri = 4 exhibit sharp, isotropic 2H-NMR lines, at t greater than tc, indicating that delta-haemolysin promotes the appearance of very small objects undergoing fast isotropic reorientation which average to zero the quadrupolar interaction. Below tc, one observes gel-phase powder patterns which indicate that the bacterial toxin is unable to form such small structures with ordered dipalmitoylglycerophosphocholine phospholipids. From comparison of the action of delta-haemolysin with that of melittin on same lipids [Dufourc et al. (1986) Biochemistry 25, 6448-6455] it results that both toxins perturb similarly fluid-phase lipids at elevated temperature, but they behave differently with gel-phase lipids, the former toxin being less efficient in membrane restructuring than the latter.

Models of delta-hemolysin membrane channels and crystal structures

Molecular modeling and energy calculations have been used to study how delta-hemolysin and melittin helices may aggregate on membrane surfaces and insert through membranes to form channels. In these models adjacent antiparallel amphipathic helices form planar "raft" structures, in which one surface is hydrophobic and the other hydrophilic. Models of delta-hemolysin crystal structure were developed using these "rafts." These models are based on the unit cell constants and the crystal symmetry obtained from the preliminary crystal data. Energy calculations favor channel models of delta-hemolysin with six or eight monomers per channel.

Surface hydrophobicity and electrophoretic mobilities of staphylococcal exotoxins with special reference to toxic shock syndrome toxin-1

The surface hydrophobicities of eleven staphylococcal toxins were estimated and compared with those of standard proteins on an octyl agarose column by high-performance hydrophobic-interaction chromatography (HP-HIC). Staphylococcal enterotoxins (SE) D, C3, C2, C1 and B showed a low surface hydrophobicity whereas alpha-toxin and gamma-toxin had a moderate surface hydrophobicity. SEA, toxic shock syndrome toxin-1 (TSST-1) and staphylococcal epidermolytic toxin (SET) showed high surface hydrophobicity and delta-toxin was the most hydrophobic protein. The electrophoretic mobility of the toxins was determined by free zone electrophoresis (FZE). All toxins except SEC1 and one of the two SEA species showed negative charge at pH 8.6. Charge heterogeneity was observed in SEA, SEC1, SEC3 and TSST-1: SEA and SEC1 had two overlapping components, whereas SEC3 and TSST-1 were resolved into two distinct components. The mobilities of the two TSST-1 components were estimated at -2.12 x 10(-5) and -3.60 x 10(-5) cm2v-1s-1, respectively, at 10 degrees C, and both fractions were immunologically indistinguishable as tested by specific TSST-1 antibodies with ELISA. An asymmetric peak was obtained in hydrophobic-interaction chromatography of TSST-1 indicating heterogeneity.

Interaction of staphylococcal delta-toxin and synthetic analogues with erythrocytes and phospholipid vesicles. Biological and physical properties of the amphipathic peptides

Staphylococcal delta-toxin, a 26-residue amphiphilic peptide is lytic for cells and phospholipid vesicles and is assumed to insert as an amphipathic helix and oligomerize in membranes. For the first time, the relationship between these properties and toxin structure is investigated by means of eight synthetic peptides, one identical in sequence to the natural toxin, five 26-residue analogues and two shorter peptides corresponding to residues 1-11 and 11-26. These peptides were designed by the Edmundson wheel axial projection in order to maintain: (a) the hydrophilic/hydrophobic balance while rationalizing the sequence, (b) the alpha-helical configuration and (c) the common epitopic structure. The fluorescence of the single Trp residue was used to monitor the behaviour of the natural toxin and analogues. All 26-residue analogues were hemolytically active although to a lesser extent than natural toxin. The peptide of residues 11-26 bound lipids weakly and was hemolytic at high concentration. The peptide of residues 1-11 did not bind lipids and was hemolytically inactive. All peptides except the latter cross-reacted in immunoprecipitation tests with the natural toxin. The study of a 26-residue analogue by circular dichroism revealed an alpha-helical configuration in both the free and lipid-bound state. Changes in the fluorescence of the peptides in the presence of lipid micelles and bilayers varied according to the position of the reporter group. When bound to lipids, Trp5, Trp16 and the Fmoc-1 positions of the analogues became buried while Trp15 of the natural toxin and its synthetic replicate remained more exposed. All changes are rationalized by the proposal of an amphipathic helix whose hydrophobic face is embedded within the apolar core of bilayers while the hydrophilic and charged face remains more exposed to solvent.

Synergism of Candida albicans and delta toxin producing Staphylococcus aureus on mouse mortality and morbidity: protection by indomethacin

Twelve Staphylococcus aureus strains, six positive and six negative for delta-toxin production, were studied for synergistic effects on mouse mortality and morbidity when combined with Candida albicans and inoculated intraperitoneally (i.p.). S. aureus strains producing delta-toxin were found to exhibit a relatively great synergistic decrease (between near 10(3)-10(5)-fold) in LD50 (dose necessary to kill 50% of exposed animals in five days) when combined with a nonlethal dose of C. albicans and injected i.p. S. aureus strains which did not produce delta showed less of a synergistic effect with C. albicans (10-10(2)-fold drop in LD50). A synergistic effect on mortality could also be produced when animals were dually injected with C. albicans and sterile growth filtrates from the delta-toxin producing strains or the purified delta-toxin. The lethal agent in the culture filtrate was, like delta-toxin, sensitive to lecithin and insensitive to heat. Indomethacin protected animals from the C. albicans-filtrate induced death. Blood measurements made following i.p. injection of delta-toxin and C. albicans revealed chemistry changes indicative of shock, kidney and liver damage; delta-toxin alone caused no significant chemistry changes whereas C. albicans alone caused some blood chemistry changes but liver and kidney damage was not indicated. No synergism on mortality was found between C. albicans and purified alpha-toxin or toxic shock syndrome toxin-1.

The amino acid sequence of a gonococcal growth inhibitor from Staphylococcus haemolyticus

A gonococcal inhibitor produced by Staphylococcus haemolyticus was separated into three components by reverse-phase h.p.l.c. The amino acid composition analysis of each of the three components indicated extensive similarities. N-Terminal sequence analysis of all three components allowed the identification of the first 27-30 residues of each. The complete primary structure of each component was determined from the sequence analysis of trypic peptides and peptides generated by mild acid hydrolysis. Each component is composed of 44 amino acid residues, with evidence suggesting the presence of an N-terminal formylmethionine residue in each. The components I, II and III have respectively 33, 29 and 33 identical amino acid residues in their sequences, which represents 75%, 65.9% and 75% homology. These components contain a high proportion of hydrophobic amino acids, and their hydrophobicity profiles are closely related. Also, each of the three components contains a positively charged residue (lysine) as the third residue, followed by a core of hydrophobic residues. These results suggest that the three components are possible signal sequences of one or more secreted or membrane-associated proteins.

Phospholipase D activity of Vibrio damsela cytolysin and its interaction with sheep erythrocytes

Exposure of sheep erythrocytes to sublytic amounts of Vibrio damsela cytolysin markedly reduced their membrane sphingomyelin content and their sensitivity to lysis by the sphingomyelin-dependent cytolysins staphylococcal sphingomyelinase C (beta-toxin) and helianthin. The toxin was found to be a phospholipase D active against sphingomyelin.

Staphylococcal toxins: screening of burn wound isolates and evidence for alpha-haemolysin production in the burn wound

Culture filtrates of Staphylococcus aureus strains isolated from burn patients were examined for cytotoxic activities. A large molecular weight cytotoxin (MW = 253,000 daltons) that exhibited cytotoxicity for human foreskin cells and haemolytic activity against human and rabbit erythrocytes was identified. The cytotoxic activity could be completely neutralized by antiserum formed against the cytotoxin. Further characterization of the molecule by isoelectric focusing revealed that the cytotoxin was composed of at least two toxic factors of smaller molecular weight. Both factors exhibited cytotoxicity to tissue-culture cells; however, one factor lysed rabbit but not human erythrocytes whereas the other factor had the opposite haemolytic pattern. The cytotoxicity of each factor was neutralized by the antiserum formed against the cytotoxin. A cytotoxic factor that exhibited haemolytic activity for rabbit erythrocytes, and that was neutralized by the cytotoxin antiserum, was identified in burn wound extracts of mice infected with Staph. aureus. On the basis of molecular weight and isoelectric focusing data, we conclude that the large molecular weight cytotoxin was composed of an aggregation of alpha-haemolysin and another presently unidentified toxic molecule, possibly delta-toxin. Alpha-haemolysin appears to be produced in vivo during experimental staphylococcal burn wound infection.

Delta-like toxin produced by coagulase-negative staphylococci is associated with neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a serious neonatal disorder of uncertain cause, although fecal bacteria have been implicated in some outbreaks. We examined coagulase-negative staphylococci (CONS) as possible etiologic agents. In our unit, CONS colonized the bowels of most infants studied, including 46% of 70 NEC cases (mean concentration, 10(9.1) CFU/g of stool). Over 90% of tested isolates produced a hemolysin resembling delta toxin of Staphylococcus aureus. Toxin purified from a NEC-associated isolate of Staphylococcus epidermidis resembled reference delta toxin from S. aureus in size, biologic properties, and antigenicity. This delta-like toxin was enteropathic, causing mucosal necrosis and hemorrhage in injected loops of the bowels of infant rats. Adjacent, nonexposed bowel remained normal, as did loops injected with lecithin-neutralized toxin. Using a new enzyme-linked immunosorbent assay (ELISA), we detected delta-like toxin in the stools of 11 of 35 infants colonized with CONS positive for delta-like toxin (Tox+). Positive tests were strongly associated with NEC. Of 18 cases with Tox+ CONS, 10 were positive (56%), whereas only 1 of 17 control infants so colonized was positive (6%, P = 0.002). In NEC patients, the mean fecal toxin concentration was 1,012 ng/g. Toxicity to fibroblasts was demonstrable in filtrates of each of six ELISA-positive samples tested but was absent in all five ELISA-negative samples tested. We conclude that delta-like toxin is elaborated in the bowels of some infants with Tox+ CONS, and its association with NEC suggests that such CONS are enteropathic. In our unit, this mechanism was apparent in 23% of 44 recent cases of endemic NEC.

Crystallization of the delta toxin of Staphylococcus aureus

Delta toxin is a small cytolytic polypeptide produced and secreted by the organism Staphylococcus aureus and belongs to a family of surface-active toxins that exhibit pronounced effects on a wide variety of cellular membranes. Although this class of proteins has been much studied by a wide variety of physical techniques, no consensus has been reached on their mode of action. Therefore, in order to investigate their role in causing membrane damage, a structural analysis of the delta toxin has been initiated. Crystals of this protein have been grown by dialysis against mixtures of 2-methylpentan-2,4-diol and water. These crystals are relatively insensitive to radiation damage and diffract to high resolution. The results of this study should provide a valuable insight into the cytolytic properties of these molecules.

In vitro synthesis of the delta-lysin of Staphylococcus aureus

The stability of mRNA for the delta-lysin of Staphylococcus aureus was determined by measuring the residual lysin synthesis after inhibition of DNA-dependent RNA polymerase activity with rifampin. At the late logarithmic-early stationary phase of growth the delta-lysin mRNA was very stable, with a half-life of ca. 20 min. Total cellular RNA was extracted from S. aureus and translated with a modified Escherichia coli S-30 system; delta-lysin was identified amongst the translation products by immunoprecipitation and immunoabsorption. The delta-lysin synthesized in vitro was of a size similar to mature delta-lysin and did not require a signal sequence for secretion from the cell.

Membrane damage by staphylococcal alpha-toxin to different types of cultured mammalian cell

Staphylococcal alpha-toxin was shown to be more membrane-damaging to epithelial-like cells than to neuroblasts or normal fibroblasts. Mouse adrenal cortex tumor (Y1Ac) epithelioid cells and human embryonal lung (MRC-5) fibroblasts were used for further comparison. Alpha-toxin was considerably more cytotoxic to adrenal cells than to fibroblasts. This difference did not depend on the presence fibronectin on the fibroblast surface, or on a general difference in the response to other membrane-damaging hemolytic toxins and detergents. Incubation of adrenal cells at 0 degree C with alpha-toxin induced some irreversible change, and membrane damage and a cytotoxic effect developed upon further incubation in toxin-free growth medium. In fibroblasts the membrane damage progressed slowly and only in the continued presence of the toxin. Toxin-induced damage to transport and synthetic functions in fibroblasts was reversible upon removal of the toxin after prolonged exposure. It is proposed that adrenal cells may carry a cell-surface receptor to which alpha-toxin binds specifically, thereby allowing the toxin to exert its cell damaging effect.

Photolabeling of staphylococcal alpha-toxin from within rabbit erythrocyte membranes

Intrinsic membrane proteins of rabbit red blood cells were labeled with the photoreactive amphipatic reagent 12-(4-azido-2-nitrophenoxy) stearoyl (1-14C) glucosamine, which inserts into the hydrophobic membrane region and generates a reactive nitrene upon ultraviolet irradiation. Photolabeling of membrane-bound staphylococcal alpha-toxin after lysis of probe-treated rabbit red blood cells by this toxin implies its penetration into the hydrophobic region of the outer leaflet of the membrane. In contrast clostridial theta-toxin and staphylococcal delta-toxin were not labeled, but extraction of intrinsic membrane proteins by delta-toxin was evidenced.

Survival of cultured cells after functional and structural disorganization of plasma membrane by bacterial haemolysins and phospholipases

Lesions were induced in the plasma membranes of cultured human fibroblasts by membrane damaging toxins of bacterial origin (haemolysins). Structural disorganization of the membrane was measured as leakage of a radiolabelled small cytoplasmic marker and functional membrane damage was measured as decreased uptake of aminoisobutyrate. Cell survival was scored 24 and 48 hr later by measuring uptake of Trypan Blue and by light microscopical evaluation of cell morphology and proliferation. The membrane damage induced by most bacterial toxins was reversible upon removal of the toxin, since toxin-treated cells recovered and excluded Trypan Blue although they had been permeable to the dye immediately after the toxin treatment. Among ten bacterial toxins tested, the only exception of this general behavior was the Aeromonas hydrophila beta-haemolysin, which irreversibly damaged human fibroblasts. Thus, the action of bacterial haemolysins on cultured cells generally seems restricted to a plasma membrane permeabilization, which is reversible regardless of the mechanism of membrane damaging action of the toxin or of the relative size of the structural lesions induced. Furthermore, the use of Trypan Blue uptake as a measure of cell death caused by membrane damaging agents appears to be of limited value.