Heat stability and species range of purified staphylococcal alpha-toxin

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

Genotypic and Phenotypic Characterization of Some psms Hypervirulent Clinical Isolates of Staphylococcus aureus in a Tertiary Hospital in Hefei, Anhui

Background

Staphylococcus aureus is a highly successful pathogen that can cause various infectious diseases, from relatively mild skin infections to life-threatening severe systemic diseases. The widespread pathogenicity of S. aureus is mainly due to its ability to produce many virulence factors that help destroy various host cells, causing disease. Our primary goal in this study was to explore the genes of highly virulent strains, to identify genes closely associated with high virulence, and to provide ideas for the treatment of infection by highly virulent clinical strains.

Results

This study collected 221 clinical strains from The First Affiliated Hospital Of The University of Science and Technology of China (USTC); their hemolytic abilities were tested. Eight isolates were selected based on their highly hemolytic ability and tested their hemolytic activity again; their phenotypes and gene sequences were also explored. Whole-genome sequencing (WGS) showed six plasmids (pN315, pNE131, pSJH901, pSJH101, SAP106B, and MSSA476), eight antibiotic resistance genes [blaR1, blaI, blaZ, mecA, erm(C), erm(T), tet(38), and fosB-Saur] and seventy-two virulence related genes. Three highly virulent strains, namely X21111206, 21092239, and 21112607, were found according the Galleria mellonella infection model. Therefore, we selected 10 representative virulence genes for qRT-PCR: psmα, psmβ, hlgA, hlgB, hlgC, hla, clfA, clfB, spa, and sak. Among them, the expression levels of psmα and psmβ, the three isolates, were significantly higher than the positive control NCTC8325.

Conclusion

Significant differences appear in the expression of virulence genes in the highly virulent strains, particularly the psmα and psmβ, It may be that the high expression of psm gene is the cause of the high virulence of Staphylococcus aureus. We can reduce the pathogenicity of Staphylococcus aureus by inhibiting the expression of psm gene, which may provide a strong basis for psm as a new target for clinical treatment of S. aureus infection.

Identification of a Human Anti-Alpha-Toxin Monoclonal Antibody Against Staphylococcus aureus Infection

Staphylococcus aureus is a major pathogenic bacterium that causes a variety of clinical infections. The emergence of multi-drug resistant mechanisms requires novel strategies to mitigate S. aureus infection. Alpha-hemolysin (Hla) is a key virulence factor that is believed to play a significant role in the pathogenesis of S. aureus infections. In this study, we screened a naïve human Fab library for identification of monoclonal antibodies targeting Hla by phage display technology. We found that the monoclonal antibody YG1 blocked the Hla-mediated lysis of rabbit red blood cells and inhibited Hla binding to A549 cells in a concentration-dependent manner. YG1 also provided protection against acute peritoneal infection, bacteremia, and pneumonia in murine models. We further characterized its epitope using different Hla variants and found that the amino acids N209 and F210 of Hla were functionally and structurally important for YG1 binding. Overall, these results indicated that targeting Hla with YG1 could serve as a promising protective strategy against S. aureus infection.

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.

Novel human monoclonal antibodies targeting the F subunit of leukocidins reduce disease progression and mortality caused by Staphylococcus aureus

Background

Staphylococcus aureus is a leading cause of Gram-positive bacterial infections worldwide; however, the treatment of S. aureus infection has become increasingly difficult due to the prevalence of methicillin-resistant S. aureus strains, highlighting the urgent need for the development of novel strategies. The complexity of S. aureus pathogenesis relies on virulence factors. Recent studies have demonstrated that leukocidins expressed by the majority of clinical isolates play important roles in the pathogenesis of S. aureus.

Results

In this study, we developed three human monoclonal antibodies against all F-components of leukocidins HlgABC, LukSF, and LukED with high affinity. These antibodies were found to be capable of blocking leukocidin-mediated cell lysis in vitro. Furthermore, the antibodies dramatically reduced disease progression and mortality after S. aureus infection in vivo.

Conclusions

Our findings revealed that neutralizing bicomponent leukocidins may be a promising strategy to combat infections caused by S. aureus.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1312-7) contains supplementary material, which is available to authorized users.

α-Toxin Induces Platelet Aggregation and Liver Injury during Staphylococcus aureus Sepsis

During sepsis, small blood vessels can become occluded by large platelet aggregates of poorly understood etiology. During Staphylococcal aureus infection, sepsis severity is linked to the bacterial α-toxin (α-hemolysin, AT) through unclear mechanisms. In this study, we visualized intravascular events in the microcirculation and found that intravenous AT injection induces rapid platelet aggregation, forming dynamic micro-thrombi in the microcirculation. These aggregates are retained in the liver sinusoids and kidney glomeruli, causing multi-organ dysfunction. Acute staphylococcal infection results in sequestration of most bacteria by liver macrophages. Platelets are initially recruited to these macrophages and help eradicate S. aureus. However, at later time points, AT causes aberrant and damaging thrombosis throughout the liver. Treatment with an AT neutralizing antibody (MEDI4893^∗) prevents platelet aggregation and subsequent liver damage, without affecting the initial and beneficial platelet recruitment. Thus, AT neutralization may represent a promising approach to combat staphylococcal-induced intravascular coagulation and organ dysfunction.

Staphylococcus aureus VraX specifically inhibits the classical pathway of complement by binding to C1q

VraX is a protein secreted by Staphylococcus aureus, an important human pathogen. A dramatic over expression of VraX is observed when S. aureus is exposed to several antimicrobial agents; however, its function remains unclear. Here, we aimed to reveal the function of this protein and the mechanism by which it affects the immune system to enhance the pathogenesis of the bacterium. Our results showed that VraX specifically inhibited the classical pathway of the complement system. In particular, VraX could bind to the C1q protein and block the formation of the C1 complex. Deletion of VraX decreased the pathogenesis of S. aureus. Our findings indicate that over expression of VraX might be a protective response for S. aureus survival.

CcpA Affects Infectivity of Staphylococcus aureus in a Hyperglycemic Environment

Many bacteria regulate the expression of virulence factors via carbon catabolite responsive elements. In Gram-positive bacteria, the predominant mediator of carbon catabolite repression is the catabolite control protein A (CcpA). Hyperglycemia is a widespread disorder that predisposes individuals to an array of symptoms and an increased risk of infections. In hyperglycemic individuals, the bacterium Staphylococcus aureus causes serious, life-threatening infections. The importance of CcpA in regulating carbon catabolite repression in S. aureus suggests it may be important for infections in hyperglycemic individuals. To test this suggestion, hyperglycemic non-obese diabetic (NOD; blood glucose level ≥20 mM) mice were challenged with the mouse pathogenic S. aureus strain Newman and the isogenic ccpA deletion mutant (MST14), and the effects on infectivity were determined. Diabetic NOD mice challenged with the ccpA deletion mutant enhanced the symptoms of infection in an acute murine pneumonia model relative to the parental strain. Interestingly, when diabetic NOD mice were used in footpad or catheter infection models, infectivity of the ccpA mutant decreased relative to the parental strain. These differences greatly diminished when normoglycemic NOD mice (blood glucose level ≤ 10 mM) were used. These data suggest that CcpA is important for infectivity of S. aureus in hyperglycemic individuals.

Basis of virulence in a Panton-Valentine leukocidin-negative community-associated methicillin-resistant Staphylococcus aureus strain

Community-associated (CA) infections with methicillin-resistant Staphylococcus aureus (MRSA) are on a global rise. However, analysis of virulence characteristics has been limited almost exclusively to the US endemic strain USA300. CA-MRSA strains that do not produce Panton-Valentine leukocidin (PVL) have not been investigated on a molecular level. Therefore, we analyzed virulence determinants in a PVL-negative CA-MRSA strain, ST72, from Korea. Genome-wide analysis identified 3 loci that are unique to that strain, but did not affect virulence. In contrast, phenol-soluble modulins (PSMs) and the global virulence regulator Agr strongly affected lysis of neutrophils and erythrocytes, while α-toxin and Agr had a major impact on in vivo virulence. Our findings substantiate the general key roles these factors play in CA-MRSA virulence. However, our analyses also showed noticeable differences to strain USA300, inasmuch as α-toxin emerged as a much more important factor than PSMs in experimental skin infection caused by ST72.

Staphylococcus aureus α-toxin: nearly a century of intrigue

Staphylococcus aureus secretes a number of host-injurious toxins, among the most prominent of which is the small β-barrel pore-forming toxin α-hemolysin. Initially named based on its properties as a red blood cell lytic toxin, early studies suggested a far greater complexity of α-hemolysin action as nucleated cells also exhibited distinct responses to intoxication. The hemolysin, most aptly referred to as α-toxin based on its broad range of cellular specificity, has long been recognized as an important cause of injury in the context of both skin necrosis and lethal infection. The recent identification of ADAM10 as a cellular receptor for α-toxin has provided keen insight on the biology of toxin action during disease pathogenesis, demonstrating the molecular mechanisms by which the toxin causes tissue barrier disruption at host interfaces lined by epithelial or endothelial cells. This review highlights both the historical studies that laid the groundwork for nearly a century of research on α-toxin and key findings on the structural and functional biology of the toxin, in addition to discussing emerging observations that have significantly expanded our understanding of this toxin in S. aureus disease. The identification of ADAM10 as a proteinaceous receptor for the toxin not only provides a greater appreciation of truths uncovered by many historic studies, but now affords the opportunity to more extensively probe and understand the role of α-toxin in modulation of the complex interaction of S. aureus with its human host.

Complete nucleotide sequence and molecular characterization of hemolysin II gene from Bacillus cereus

Hemolysin II gene from Bacillus cereus VKM-B771 has been sequenced. The deduced primary translation product consists of 412 amino acid residues which corresponds to the protein with an M(r) of 45.6 kDa. The predicted mature Hly-II protein (residues 32 to 412) is of 42.3 kDa, which is in close agreement with the mini-cell electrophoresis analysis. Hly-II deletion variant lacking 96 C-terminal residues still has hemolytic activity. The protein primary structure analysis revealed no homology with any known Bacillus cytolysins. Significant general homology (31-28% identity) was found between the hemolysin II and Staphylococcus aureus alpha-toxin, gamma-hemolysin (HlgB), and leukocidins (LukF, LukF-R, LukF-PV). The data suggest that hemolysin II belongs to the group of beta-channel forming cytolysins.

alpha-Hemolysin from Staphylococcus aureus: an archetype of beta-barrel, channel-forming toxins

alpha-Hemolysin, secreted from Staphylococcus aureus as a water-soluble monomer of 33.2 kDa, assembles on cell membranes to form transmembrane, heptameric channels. The structure of the detergent-solubilized heptamer has been determined by X-ray crystallography to 1.9 A resolution. The heptamer has a mushroom-like shape and measures up to 100 A in diameter and 100 A in height. Spanning the length of the molecule and coincident with the molecular sevenfold axis is a water-filled channel that ranges in diameter from approximately 16 to approximately 46 A. A 14 strand antiparallel beta-barrel, in which two strands are contributed by each subunit, defines the transmembrane domain. On the exterior of the beta-barrel there is a hydrophobic belt approximately 30 A in width that provides a surface complementary to the nonpolar portion of the lipid bilayer. The extensive promoter-protomer interfaces are composed of both salt-links and hydrogen bonds, as well as hydrophobic interactions, and these contacts provide a molecular rationalization for the stability of the heptamer in SDS solutions up to 65 degrees C. With the structure of the heptamer in hand, we can better understand the mechanisms by which the assembled protein interacts with the membrane and can postulate mechanisms of assembly.

Hemolytic activity of Trichomonas vaginalis and Tritrichomonas foetus

The hemolytic activity of live isolates and clones of Trichomonas vaginalis and Tritrichomonas foetus was investigated. The isolates were tested against human erythrocytes. No hemolytic activity was detected by the isolates of T. foetus. Whereas the isolates of T. vaginalis lysed erythrocytes from all human blood groups. No hemolysin released by the parasites could be detected. Our preliminary results suggest that hemolysis depend on the susceptibility of red cell membranes to destabilization and the intervention of cell surface receptors as a mechanism of the hemolytic activity. The mechanism could be subject to strain-species-genera specific variation of trichomonads. The hemolytic activity of T. vaginalis is not due to a hemolysin or to a product of its metabolism. Pretreatment of trichomonads with concanavalin A reduced levels of hemolysis by 40%.

Alpha-toxin of Staphylococcus aureus

Alpha-toxin, the major cytotoxic agent elaborated by Staphylococcus aureus, was the first bacterial exotoxin to be identified as a pore former. The protein is secreted as a single-chain, water-soluble molecule of Mr 33,000. At low concentrations (less than 100 nM), the toxin binds to as yet unidentified, high-affinity acceptor sites that have been detected on a variety of cells including rabbit erythrocytes, human platelets, monocytes and endothelial cells. At high concentrations, the toxin additionally binds via nonspecific absorption to lipid bilayers; it can thus damage both cells lacking significant numbers of the acceptor and protein-free artificial lipid bilayers. Membrane damage occurs in both cases after membrane-bound toxin molecules collide via lateral diffusion to form ring-structured hexamers. The latter insert spontaneously into the lipid bilayer to form discrete transmembrane pores of effective diameter 1 to 2 nm. A hypothetical model is advanced in which the pore is lined by amphiphilic beta-sheets, one surface of which interacts with lipids whereas the other repels apolar membrane constitutents to force open an aqueous passage. The detrimental effects of alpha-toxin are due not only to the death of susceptible targets, but also to the presence of secondary cellular reactions that can be triggered via Ca2+ influx through the pores. Well-studied phenomena include the stimulation of arachidonic acid metabolism, triggering of granule exocytosis, and contractile dysfunction. Such processes cause profound long-range disturbances such as development of pulmonary edema and promotion of blood coagulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Staphylococcal alpha toxin promotes blood coagulation via attack on human platelets

Staphylococcus aureus plays a major role as a bacterial pathogen in human medicine, causing diseases that range from superficial skin and wound to systemic nosocomial infections . The majority of S. aureus strains produces a toxin, a proteinaceous exotoxin whose hemolytic, dermonecrotic, and lethal properties have long been known (1-6). The toxin is secreted as a single- chained, nonglycosylated polypeptide with a M(r) of 3.4 x 10(4) (7, 8). The protein spontaneously binds to lipid monolayers and bilayers (9-14), producing functional transmembrane pores that have been sized to 1.5-2.0-nm diameters (15-18). The majority of pores formed at high toxin concentrations (20 mug/ml) is visible in the electron microscope as circularized rings with central pores of approximately 2 nm in diameter. The rings have been isolated, and molecular weight determinations indicate that they represent hexamers of the native toxin (7). We have proposed that transmembrane leakiness is due to embedment of these ring structures in the bilayer, with molecular flux occurring through the central channels (15, 19). Pore formation is dissectable into two steps (20, 21). Toxin monomers first bind to the bilayer without invoking bilayer leakiness . Membrane-bound monomers then laterally diffuse and associate to form non-covalently bonded oligomers that generate the pores. When toxin pores form in membranes of nucleated cells, they may elicit detrimental secondary effects by serving as nonphysiologic calcium channels, influx of this cation triggering diverse reactions, including release of potent lipid mediators originating from the arachidonate cascade (22-24). That alpha toxin represents an important factor of staphylococcal pathogenicity has been clearly established in several models of animal infections through the use of genetically engineered bacterial strains deleted of an active alpha toxin gene (25-27). Whether the toxin is pathogenetically relevant in human disease, however, is a matter of continuing debate. Doubts surrounding this issue originate from two main findings. First, whereas 60 percent hemolysis of washed rabbit erythrocytes is effected by approximately 75 ng/ml alpha toxin, approximately 100-fold concentrations are required to effect similar lysis of human cells (4-6, 13). The general consensus is that human cells display a natural resistance towards toxin attack. The reason for the wide inter-species variations in susceptibility towards alpha toxin is unknown but does not seem to be due to the presence or absence of high-affinity binding sites on the respective target cells (20, 21). Second, low-density lipoprotein (28) and neutralizing antibodies present in plasma of all healthy human individuals inactivate a substantial fraction of alpha toxin in vitro. These inactivating mechanisms presumably further raise the concentration threshold required for effective toxin attack, and it is most unlikely that such high toxin levels will ever be encountered during infections in the human organism. The aforegoing arguments rest on the validity of two general assumptions. First, the noted natural resistance of human erythrocytes to alpha toxin must be exhibited by other human cells. Second, toxin neutralization by plasma components, usually tested and quantified after their preincubation with toxin in vitro, must be similarly effective under natural conditions, and protection afforded by these components must not be restricted to specific cell species.

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.

Comparative study of Vibrio cholerae non-O1 protease and soluble hemagglutinin with those of Vibrio cholerae O1

Protease and soluble hemagglutinating activities produced by a non-O1 Vibrio cholerae strain isolated from a patient with diarrhea were compared with similar activities produced by V. cholerae O1. The soluble protease activities were indistinguishable in heat stability, immunodiffusion, inhibition by antiserum, and electrophoretic analysis. On the other hand, the soluble hemagglutinating activities of both strains were not completely identical. The hemagglutinating activity of the non-O1 V. cholerae strain was not inhibited by Zincov; it was more sensitive to inhibition by normal serum, and it had an unusual pattern of heat stability. Heating at 100 degrees C resulted in some recovery of activity of a sample previously inactivated by heating at 60 degrees C.

Enzyme-linked immunosorbent assay for detection of Staphylococcus aureus alpha-toxin

A sandwich enzyme-linked immunosorbent assay was developed for measuring Staphylococcus aureus alpha-toxin. This assay was 500 to 1,000 times more sensitive than the commonly used hemolytic titration assay and was less variable. The binding of alpha-toxin to the adsorbed antibody was most effective after an overnight incubation at 27 degrees C. The toxin was detectable even at a log2 17 dilution of an S. aureus culture supernatant.

Action of staphylococcal alpha-toxin on membranes: some recent advances

Recent developments in the area of Staphylococcal alpha-toxin studies are presented which modify the concepts previously held with respect to both biological and physical properties of alpha-toxin. New data concerning the nature of the binding site for alpha-toxin on rabbit erythrocyte membranes and a model to explain the various observed complexes of alpha-toxin and membrane receptor are discussed. Finally, evidence suggesting that Staphylococcal alpha-toxin is a potent demyelinating agent is presented.

Purification and some properties of a lethal toxic fragment of staphylococcal alpha-toxin by tryptic digestion

Purified staphylococcal alpha-toxin (molecular weight approximately 36,000) was mildly digested with trypsin, yielding two components by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A fast-moving component (molecular weight 17,000 +/- 5%) which is relatively resistant to tryptic digestion and a slow-moving component (molecular weight 20,000 +/- 5%) which tends to aggregate. The fast-moving component was highly purified by means of combined procedures of column chromatography on Sephadex G-200 with zone electrophoresis on starch. The purified fast-moving component retained a high degree of lethal toxicity for mouse but lacked hemolytic and dermonecrotic activities, whereas the slow-moving component proved to be a nontoxic polypeptide. The lethal toxic fragment was antigenically active showing partial immunological identity with the parent alpha-toxin and stimulated the formation of antibodies capable of neutralizing the lethal action of alpha-toxin in vivo. Some physical properties and the amino acid composition of the purified lethal toxic fragment have been compared with those of native alpha-toxin.

Temperature-dependent inactivating factor of Pseudomonas aeruginosa exotoxin A

The adenosine diphosphate ribosyl transferase activity of Pseudomonas aeruginosa exotoxin A(PA toxin) was found to be rapidly destroyed by heating at 45 to 60C but not by heating at 70 to 90C (for at least 30 min). This phenomenon has been previously described for other bacterial toxins (staphylococcal alpha-toxin and Vibrio parahaemolyticus hemolysin) and is termed an Arrhenius effect. In contrast, the Arrhenius effect was not seen when the PA toxin was heat-treated as above and tested for cell toxicity or mouse lethality. Although the PA toxin treated at 70C for 30 min retained a significant proportion (is greater than 70%) of its adenosine diphosphate ribosyl transferase activity, the cell toxicity and mouse lethality of the toxin were virtually abolished. A temperature-dependent inactivating factor that has proteolytic activity and is co-purified with the PA toxin was shown to be responsible for the Arrhenius effect. PA toxin separated from the factor by conventional disc gel electrophoresis or PA toxin preparations lacking the factor did not show the Arrhenius effect.

Multiple forms of staphylococcal alpha-toxin

A group of proteins was readily extracted at neutrality from trichloroacetic acid precipitates of staphylococcal culture filtrate supernatants, while alpha-toxin was dissolved and activated by treating the precipitate with 8 M urea, with acidic buffers or by heating to 90-100 degrees C at neutrality. Heat activation of the precipitate produced a relatively pure alpha-toxin with a molecular weight of 39,000. alpha-Toxin was eluted together with three other proteins on hydroxyl apatite chromatography, and evidence was obtained for an association between the four proteins. On isoelectric focusing a haemolytic fraction was obtained at pH 6.2, probably due to acid activation of the precipitate formed at the cathodic end of the column. The alpha-haemolytic fractions with pI's of 7.4 and 8.6 were shown to consist of alpha-toxin only when analyzed by acrylamide electrophoresis in the presence of sodium dodecyl sulphate. The haemolytic component with a pI of 9.2 contained two additional components of molecular weights of 27,500 and 18,000. Chromatography of this material on Sephadex G-200 showed that alpha-toxin and the two proteins appeared as a high molecular complex.

The hemolysins of Staphylococcus aureus

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Characterization of the temperature-dependent inactivating factor of the thermostable direct hemolysin in Vibrio parahaemolyticus

The termostable direct hemolysin of Vibrio parahaemolyticus is inactivated by heating at around 55 C with an inactivating factor isolated from culture filtrates of V. parahaemolyticus. The characteristics of the temperature-dependent inactivating factor were studied by using polyacrylamide gel disc electrophoresis. It was found that when heated with the hemolysin, the inactivating factor destroyed the hemolysin and thus inactivated the hemolytic activity, suggesting that the inactivating factor has proteolytic activity. It was also demonstrated that the inactivating factor itself is heat labile, losing its activity on heating with the hemolysin at 95 C for 15 min. The inactivating factor was stimulated by the presence of NaCl or MgCl2 and showed maximal activity at around pH 8.0. The results support our previous hypothesis that the Arrhenius effect observed with crude hemolysin of V. parahaemolyticus is due to the presence of a temperature-dependent inactivating factor. The fact that the factor is activated on heating at 50 to 60 C but is inactivated on heating at 70 to 100 C explains the Arrheius effect of crude hemolysin of V. parahaemolyticus.

Demonstration of a temperature-dependent inactivating factor of the thermostable direct hemolysin in Vibrio parahaemolyticus

A factor was found in Vibrio parahaemolyticus which inactivated the hemolytic activity of a purified, thermostable direct hemolysin. The inactivating factor was associated with the hemolysin but could be separated from it by diethylaminoethyl-cellulose column chromatography. The inactivating factor was activated by heating at 50 to 60 C, but was itself thermolabile and lost activity on heating to 70 to 100 C. The mechanism of the Arrhenius effect, observed with crude hemolysin of V. parahaemolyticus, is as follows. At 50 to 60 C, the temperature-dependent inactivating factor associated with hemolysin inactivates the hemolysin, whereas at 80 to 100 C the crude hemolysin retains activity because at this temperature the factor is inactivated.

Effect of heat (Arrhenius effect) on crude hemolysin of Vibrio parahaemolyticus

Crude hemolysins prepared from various strains of Vibrio parahaemolyticus, which give positive Kanagawa phenomenon, were partly inactivated by heating at 60 C, but not inactivated significantly by heating at 80 to 90 C. The similar phenomenon has been reported as the Arrhenius effect in staphylococcal alpha toxin.

Inhibition of staphylococcal alpha-toxin. A kinetic evaluation of aromatic polysulphonic acids as inhibitors of haemolysis

1. The effect of a number of aromatic polysulphonic acids on the kinetics of haemolysis of rabbit erythrocyte suspensions by crude staphylococcal alpha-toxin was studied at pH8.6 and 6.8. 2. All of the inhibitory compounds caused an increase in the prelytic lag time (tau) of the sigmoid haemolysis curves, an increase in the time to reach 50% haemolysis (t((1/2))) and a decrease in the maximum rate of haemolysis (R(max.)). The most inhibitory compounds caused a 50% decrease in R(max.) at concentrations between 0.1 and 0.2mm. 3. The effect of pH varied considerably: compounds (I) and (II) were almost equally inhibitory at both pH values, compounds (IV) and (IX) were more inhibitory at pH6.8 than at pH8.6, and compounds (VII), (VIII), (X), (XI) and (XII) were more inhibitory at pH8.6. 4. Increased time of premixing alpha-toxin with compound (I) caused increased inhibition. 5. An attempt was made, where possible, to relate the inhibitory activity to the structure of the test compound.

Physical states of staphylococcal alpha-toxin

At least three different forms of staphylococcal alpha-toxin have been shown to exist: soluble active alpha-toxin (alpha 3S), soluble inactive alpha-toxin (alpha(12s)), and insoluble inactive aggregate. Aggregation to the insoluble, biologically inactive form could be induced by brief heating to 60 C. The aggregate was dissociated by treatment with 8 m urea with reappearance of biological activity. Subsequent removal of urea by dialysis resulted in some spontaneous reaggregation to the insoluble state. The supernatant fluid obtained after dialysis contained soluble active alpha-toxin of high specific activity, possessing physical, toxic, and immunological properties closely resembling those of native toxin. The soluble biologically inert component (alpha(12s)) was identified as a third physical state. Negatively stained preparations of this material, when examined in the electron microscope, showed rings of approximately 100 A outside diameter containing 6 +/- 1 subunits.