Pneumococcal Hemolysin: The Preparation of Concentrates, and Their Action on Red Cells

Pneumolysin: Pathogenesis and Therapeutic Target

Streptococcus pneumoniae is an opportunistic pathogen responsible for widespread illness and is a major global health issue for children, the elderly, and the immunocompromised population. Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) and key pneumococcal virulence factor involved in all phases of pneumococcal disease, including transmission, colonization, and infection. In this review we cover the biology and cytolytic function of PLY, its contribution to S. pneumoniae pathogenesis, and its known interactions and effects on the host with regard to tissue damage and immune response. Additionally, we review statins as a therapeutic option for CDC toxicity and PLY toxoid as a vaccine candidate in protein-based vaccines.

Mini-review: novel therapeutic strategies to blunt actions of pneumolysin in the lungs

Severe pneumonia is the main single cause of death worldwide in children under five years of age. The main etiological agent of pneumonia is the G+ bacterium Streptococcus pneumoniae, which accounts for up to 45% of all cases. Intriguingly, patients can still die days after commencing antibiotic treatment due to the development of permeability edema, although the pathogen was successfully cleared from their lungs. This condition is characterized by a dramatically impaired alveolar epithelial-capillary barrier function and a dysfunction of the sodium transporters required for edema reabsorption, including the apically expressed epithelial sodium channel (ENaC) and the basolaterally expressed sodium potassium pump (Na+-K+-ATPase). The main agent inducing this edema formation is the virulence factor pneumolysin, a cholesterol-binding pore-forming toxin, released in the alveolar compartment of the lungs when pneumococci are being lysed by antibiotic treatment or upon autolysis. Sub-lytic concentrations of pneumolysin can cause endothelial barrier dysfunction and can impair ENaC-mediated sodium uptake in type II alveolar epithelial cells. These events significantly contribute to the formation of permeability edema, for which currently no standard therapy is available. This review focuses on discussing some recent developments in the search for the novel therapeutic agents able to improve lung function despite the presence of pore-forming toxins. Such treatments could reduce the potentially lethal complications occurring after antibiotic treatment of patients with severe pneumonia.

THE CARDIOTOXIC ACTION OF PREPARATIONS CONTAINING THE OXYGEN-LABILE HEMOLYSIN OF STREPTOCOCCUS PYOGENES : I. INCREASED SENSITIVITY OF THE ISOLATED FROG'S HEART TO REPEATED APPLICATION OF THE TOXIN

1. A study has been made of the effect on the isolated frog's heart of a preparation derived from the supernatant fluid of cultures of hemolytic streptococcus. 2. The streptococcal preparation was found to induce systolic contracture, the contracture usually developing only after the second of two administrations of the preparation. It was found that a single application of the streptococcal preparation sensitized the heart to a second application. 3. The properties of the cardiotoxic factor so far as they have been studied were found to be identical with those of the oxygen-labile hemolysin of streptococci. The capacity of normal and of immune sera to neutralize the cardiotoxic action paralleled the antihemolytic potency of the sera.

COMPARATIVE KINETICS OF HEMOLYSIS INDUCED BY BACTERIAL AND OTHER HEMOLYSINS

A study has been made of the kinetics of lysis induced by various hemolytic agents. The course of bemolysis was followed by mixing lysin with washed human erythrocytes, removing samples from the mixture, and estimating colorimetrically the hemoglobin in the supernatant fluid of the centrifuged samples. Most of the curves (but not all of them, e.g. tyrocidine) obtained by plotting degree of hemolysis against time, were S-shaped. The initiation of lysis by streptolysin S' was delayed, and in this property, streptolysin S' was similar to Cl. septicum hemolysin. None of the other lysins studied exhibited a long latent period preceding lysis. The maximum rate of hemoglobin liberation was found, in the range of lysin concentrations studied, to be a linear function of concentration when theta toxin of Cl. welchii, pneumolysin, tetanolysin, or streptolysin S' was the lytic agent. With comparable concentrations of saponin, sodium taurocholate, cetyl pyridinium chloride, tyrocidine, duponol C, lecithin-atrox venom mixture, or streptolysin O, the relation between rate and concentration was non-linear. The critical thermal increment associated with hemolysis was determined for systems containing pneumolysin, theta toxin, streptolysin S', streptolysin O, tetanolysin, and saponin. The findings concerning the effect of concentration and temperature on the rate of hemolysis provide a basis for classifying hemolytic agents (Tables I and II). Hemolysis induced by Cl. septicum hemolysin was found to be preceded by two phases: a phase of alteration of the erythrocytes and a phase involving swelling. Antihemolytic serum inhibited the first but not the second phase while sucrose inhibited the second but not the first phase.

The role of pneumolysin in pneumococcal pneumonia and meningitis

Diseases caused by Streptococcus pneumoniae include pneumonia, septicaemia and meningitis. All these are associated with high morbidity and mortality. The pneumococcus can colonize the nasopharynx, and this can be a prelude to bronchopneumonia and invasion of the vasculature space. Proliferation in the blood can result in a breach of the blood-brain barrier and entry into the cerebrospinal fluid (CSF) where the bacteria cause inflammation of the meningeal membranes resulting in meningitis. The infected host may develop septicaemia and/or meningitis secondary to bronchopneumonia. Also septicaemia is a common precursor of meningitis. The mechanisms surrounding the sequence of infection are unknown, but will be dependent on the properties of both the host and bacterium. Treatment of these diseases with antibiotics leads to clearance of the bacteria from the infected tissues, but the bacteriolytic nature of antibiotics leads to an acute release of bacterial toxins and thus after antibiotic therapy the patients can be left with organ-specific deficits. One of the main toxins released from pneumococci is the membrane pore forming toxin pneumolysin. Here we review the extensive studies on the role of pneumolysin in the pathogenesis of pneumococcal diseases.

The purification and properties of streptolysin S

Considerable purification of streptolysin S has been achieved by fractionation of crude bacterial filtrates with methanol, under controlled conditions of pH, ionic strength, and temperature. The final material (P III) consisted of two electrophoretic components. The purified material was employed for kinetic studies, the results of which were confirmed with hemolysin isolated electrophoretically from P III. The heat of activation (temperature characteristic) of streptolysin S was found to be 17,900 calories per mole. Time dilution curves of the hemolysin were found to be sigmoid. The influence of certain ions and lipids on the course of hemolysis was investigated. The significance of the prolonged lag period and of the deviation in the behavior of streptolysin S from Ponder's equation has been discussed.

LYSIS OF BACTERIAL PROTOPLASTS AND SPHEROPLASTS BY STAPHYLOCOCCAL ALPHA-TOXIN AND STREPTOLYSIN S

Bernheimer, Alan W. (New York University School of Medicine, New York, N.Y.), and Lois L. Schwartz. Lysis of bacterial protoplasts and spheroplasts by staphylococcal alpha-toxin and streptolysin S. J. Bacteriol. 89:1387-1392. 1965.-Protoplasts of Bacillus megaterium, Sarcina lutea, and Streptococcus pyogenes, and spheroplasts of Escherichia coli were lysed by staphylococcal alpha-toxin, whereas spheroplasts of Vibrio metschnikovii and V. comma were not. In the spectrum of its lytic action, streptolysin S qualitatively resembled staphylococcal alpha-toxin except for failure to lyse S. pyogenes protoplasts. In contrast to the two foregoing agents, streptolysin O did not lyse protoplasts and spheroplasts. The observations are interpreted in relation to similarities and differences in lipid composition of bacterial and mammalian cell membranes.

Production and purification of Streptococcus pneumoniae hemolysin (pneumolysin)

Pneumolysin was found to be produced by 112 of 113 clinical isolates of Streptococcus pneumoniae and to be an intracellular hemolysin. A 10-liter-scale fermentor production and purification procedure was developed for this hemolysin. The culture was concentrated by filtration 10 times before centrifugation. The cellular content was purified by ion-exchange chromatography, covalent thiopropyl gel chromatography, and gel filtration. One batch operation resulted in 6 mg of highly purified pneumolysin, with a yield of 66% and a specific activity of 1,400,000 hemolytic units per mg. The pneumolysin had a molecular weight of 53,000 and an isoelectric point of 5.2. The purification method developed will be of value in future studies on this hemolysin.

Purification of pneumolysin

A procedure for the purification of pneumolysin has been developed. Its use results in a 96-fold increase in specific activity from the original crude pneumococcal extract to the final purified product. The purified material is heat-labile and is inactivated by trypsin and cholesterol; inactivation by p-hydroxymercuribenzoate can be reversed by mercaptoethanol. Intravenous administration of the material to rabbits results in crenation, increased osmotic fragility, and intravascular lysis of the erythrocytes of the animal.

Staphylococcal leucocidins

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