PNEUMOCOCCUS HEMOTOXIN

Insights into the Evolutionary Relationships of LytA Autolysin and Ply Pneumolysin-Like Genes in Streptococcus pneumoniae and Related Streptococci

Streptococcus pneumoniae (pneumococcus) is a major human pathogen. The main pneumococcal autolysin LytA and the pneumolysin Ply are two of the bacterium's most important virulence factors. The lytA- and ply-related genes are also found in other streptococci of the Mitis group (SMG). The precise characteristics of the lytA-related-but not the ply-related-genes of SMG and their prophages have been previously described. A search of the more than 400 SMG genomic sequences available in public databases (ca. 300 for S. pneumoniae), showed Streptococcus pseudopneumoniae IS7493 to harbor four ply-related genes, two of which (plyA and plyB) have 98% identical nucleotides. The plyA homolog of S. pseudopneumoniae is conserved in all S. pneumoniae strains, and seems to be included in a pathogenicity island together with the lytA gene. However, only nonencapsulated S. pneumoniae strains possess a plyB gene, which is part of an integrative and conjugative element. Notably, the existence of a bacterial lytA-related gene in a genome is linked to the presence of plyA and vice versa. The present analysis also shows there are eight main types of plyA-lytA genomic islands. A possible stepwise scenario for the evolution of the plyA-lytA island in S. pneumoniae is proposed.

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 SERUM FERMENTS AND ANTIFERMENT DURING PNEUMONIA : STUDIES ON FERMENT ACTION. XXIV

1. The crisis in pneumonia is usually accompanied by (a) decrease in the serum antiferment; (b) the mobilization of a non-specific protease in the serum; (c) an increase in serum lipase; (d) a decrease in the non-coagulable nitrogen, and of the proteoses in the serum. 2. The crisis is associated with the beginning of an active autolysis, the latter depending on an altered relation between the ferment-antiferment balance. 3. The fibrin and leucocytic debris must be considered as one of the potential sources of toxic substances. With rapid autolysis proceeding, only non-toxic materials are absorbed.

STUDIES ON THE OXIDATION AND REDUCTION OF IMMUNOLOGICAL SUBSTANCES : X. IMMUNOLOGICAL DISTINCTIONS BETWEEN THE HEMOTOXIN AND THE "PROTEIN FRACTION" OF THE PNEUMOCOCCUS CELL

The investigation deals with the immunological differentiation of the hemotoxin and the "protein fraction" of Pneumococcus, and with a like differentiation of the antihemotoxin and the antiprotein precipitins. The distinction is made upon the basis of the following evidence: (1) The antigenic (antibody-invoking and antibody-combining) properties of the hemotoxin were destroyed by heat and oxidation treatments which did not cause the loss of the antigenic effectiveness of the "protein fraction." (2) The removal of the hemotoxin from pneumococcus solutions by combination with erythrocytes caused no loss in the capacity of the solution to invoke the production of antiprotein precipitins nor in its capacity to react with antiprotein immune serum. Titrations of the antihemotoxin content of antipneumococcus horse serum (both diagnostic and therapeutic) indicated that the heating treatment of the immunization material is the most important factor in determining the antihemotoxin content of the immune sera obtained from horses, as well as of that from rabbits. A distinction was also made between the hemotoxin and the toxic substances ("endotoxin") which cause the acute anaphylactoid death of rabbits.

STUDIES ON OXIDATION AND REDUCTION BY PNEUMOCOCCUS : IV. OXIDATION OF HEMOTOXIN IN STERILE EXTRACTS OF PNEUMOCOCCUS

In the present work on oxidation and reduction by sterile extracts of pneumococcus, the preparations employed contain among other constituents, a hemolytic substance the properties of which have been described by Cole (1, 2) in his studies on pneumococcus hemotoxin. Pneumococcus extracts prepared by the methods described are actively hemolytic, 0.005 cc. of extract causing complete lysis of 2.5 cc. of a 1 per cent suspension of red cells from rabbit blood. This hemolytic property of pneumococcus extracts is destroyed by 10 minutes exposure to 55°C. When pneumotoxin-containing extracts are protected from the action of molecular oxygen, their hemolytic activity remains unimpaired for considerable periods of time. In the presence of air, on the other hand, the stability of the hemolytic substance depends upon whether the particular type of extract contains a "complete" or "incomplete" oxidation-reduction system. Sterile broth extracts of unwashed pneumococci are reactive with molecular oxygen, and as a result of this union peroxide is formed whenever these extracts are exposed to air. The hemolytic activity of "complete" extracts of this type is rapidly decreased and finally destroyed in the presence of molecular oxygen. On the other hand, the "incomplete" type of extract prepared by saline extraction of washed pneumococci may be exposed to air with little or no loss of hemolytic power. This "incomplete" washed cell extract, unless reactivated, does not undergo autoxidation in the presence of air; under these circumstances peroxide is not formed and the hemolytic activity of this type of extract is not impaired by exposure to air. The stability of the hemolytic agent in the "incomplete" type of extract is evidence that this substance is itself not reactive with or affected by molecular oxygen, even in the presence of the cell enzymes. The destruction of the same hemolytic substance in extracts capable of undergoing autoxidation may be ascribed to the action of some peroxide formed by the union of molecular oxygen with easily oxidized or autoxidizable substances of the extract. It is now known that a peroxide, having the reactions of hydrogen peroxide, accumulates in sterile pneumococcus extracts during oxidation. It has been shown in the present study that the addition of preformed hydrogen peroxide destroys the hemolytic activity of pneumococcus extracts, although higher concentrations were required than were detected in oxidized extracts themselves. These facts and the known action of superoxides in analogous types of reaction make it seem not unlikely that the active agent in the destruction of pneumotoxin in oxidized cell extracts may be a peroxide; either hydrogen peroxide or some higher organic peroxide formed during autoxidation of the extract.

GROWTH-INHIBITORY SUBSTANCES IN PNEUMOCOCCUS CULTURES

The known factors concerned in the autoinhibition of growth of pneumococcus are: 1. The accumulation of acid products of metabolism, resulting in unfavorable reaction changes in the medium. 2. The exhaustion of the nutritive substances of the medium. 3. Under certain cultural conditions the formation and accumulation of peroxide in the medium.

THE ANTIGENIC PROPERTIES OF SOLUTIONS OF PNEUMOCOCCUS

1. Intact pneumococci, possessing specific antigenic powers unimpaired by cultural or other procedures, give rise to agglutinins for organisms of the homologous type and to precipitins for the type-specific carbohydrate derived from them. 2. Solutions of pneumococci free of all formed elements, but containing the carbohydrate and protein of the original cell, fail to stimulate the formation of type-specific antibodies. Sera prepared in this manner do not react with the carbohydrate constituent of the cell and do not agglutinate organisms of the homologous type. The loss of this antigenic function is related to changes incurred during dissolution of the bacterial cell. 3. Solutions of the cellular substances of Pneumococcus, although lacking the specific antigen of the whole cell, induce the formation of antibodies reactive with pneumococcus protein regardless of the type from which the latter is derived.

THE PRODUCTION OF METHEMOGLOBIN BY PNEUMOCOCCI

1. Pneumococci in contact with hemoglobin transform this into methemoglobin. This reaction occurs only when the pneumococci are living; it is not induced by the culture fluid or by extracts of the bacteria. 2. The reaction does not occur when hemoglobin is added to an emulsion of washed pneumococci in salt solution. However, if minute traces of dextrose be added to such a mixture, the reaction quickly occurs. The dextrose may be replaced by any one of a number of other sugars, and also by certain other organic substances, if the latter are added in large amounts. Certain other organic substances are not able to replace dextrose, but it has been impossible to determine any special molecular configuration on which this property depends. 3. The formation of methemoglobin by pneumococci probably resembles the formation of methemoglobin by certain chemical substances, such as aminophenol. 4. From the work of others it is probable that the formation of methemoglobin is always a reaction of oxidation. In the formation of methemoglobin by reducing agents, the latter are first oxidized, this occurring better in the presence of oxyhemoglobin. In certain instances an alternate oxidative and reduction of the transforming agent occurs, so that the reaction is continuous. The effect which the presence or absence of free oxygen has on the reaction with pneumococci suggests that this follows similar lines. 5. The reaction does not occur in the absence of oxygen. If the free oxygen be first removed, and then replaced, the reaction occurs more rapidly than if the oxygen had not been removed. The presence of free oxygen in excess slightly delays the reaction, possibly because of the inhibition of the reduction process which forms the first part of the reaction. 6. The explanation of this phenomenon of methemoglobin production is not only of importance so far as this special reaction is concerned, but also because it suggests an explanation for the manner in which pathological effects are produced by those bacteria which apparently produce no soluble toxin.

STUDIES ON THE OXIDATION AND REDUCTION OF IMMUNOLOGICAL SUBSTANCES : I. PNEUMOCOCCUS HEMOTOXIN

Pneumococcus hemotoxin, an antigenic substance of bacterial origin, is converted by oxidation to a product devoid of hemolytic action. The oxidation product of the hemotoxin may be converted to the original hemolytic substance by reduction, by the anaerobic action of certain bacteria, or by sodium hydrosulfite. The active lysin, or hemotoxin, produced by the reduction of the inactive oxidized extracts is identical with the original, active, reduced hemotoxin; it possesses the same degree of thermolability and is neutralized by the same specific antibody. The inactive products formed by heating the hemotoxin anaerobically cannot be "reactivated" by reducing agents. The immunological significance of these relations will be discussed in a subsequent paper.

Biological properties of pneumolysin

Pneumolysin is a thiol-activated membrane-damaging toxin produced by Streptococcus pneumoniae. The toxin plays a role in virulence of the pneumococcus in animal models of infection. Pneumolysin has a range of biological activity including the ability to lyse eukaryotic cells and to interfere with the function of cells and soluble molecules of the immune system. The use of purified native and mutant toxin and of isogenic mutants of the pneumococcus expressing altered versions of the toxin has allowed the contribution of the various activities of this multifunctional toxin to virulence to be defined.

Pneumococcal virulence factors and host immune responses to them

The principal virulence determinant of most encapsulated bacterial pathogens is the possession of an extracellular capsule. This paper discusses biological aspects of the Streptococcus pneumoniae capsule, putative roles played by accessory virulence factors of this pathogen and prospects for improvement of the currently available pneumococcal vaccine. Even though the interruption of genes encoding selected proteins has been shown to attenuate virulence to some degree, the physical removal of the pneumococcal capsule or the interruption of encapsulation genes completely abolishes virulence in mice. The role of the capsule in pathogenesis is not completely clear, however, since it is not known whether this structure is important in colonization, the obligatory first step in the process. In addition, a number of proteins have been implicated as possible accessory virulence factors. These include pneumolysin, two distinct neuraminidases, an IgA1 protease and two surface proteins, pspA and psaA. While interruption of the expression of some of these proteins examined to date has been shown to attenuate virulence, so far it has not proven possible to completely abolish virulence in this fashion. Proteinaceous accessory virulence factors may prove important to the development of second-generation pneumococcal vaccines, however. Pneumococcal and other proteins conjugated to pneumococcal polysaccharides are currently being evaluated as carriers in attempts to improve the immunogenicity of polysaccharide vaccines, primarily in small children.

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.

Pneumococci producing beta hemolysis on agar

Fifty-six strains of pneumococci were studied for hemolysis on blood-agar Twenty-two (39%) of these strains produced beta hemolysis on agar containing horse red cells, six (11%) were beta hemolytic for sheep cells, and none lysed human or rabbit red cells. The substance producing beta hemolysis appeared after 24 hr of anaerobic incubation. Subsequent exposure to air at low temperature (6 to 20 C) for 48 hr was needed to activate it. There was no relation between serological type and beta hemolysis production. This substance appears to be different from the pneumococcal hemolysin previously described.

THE PRODUCTION OF SKIN NECROSIS BY CERTAIN AUTOLYSATES OF PNEUMOCOCCUS (TYPES I AND II)

1. Certain pneumococcus autolysates produce necrosis when injected into the skin of guinea pigs. 2. The necrosis-producing principle can be filtered through a Berkefeld N filter, is extremely thermolabile, and is very sensitive to oxidation. 3. The necrotizing poison can be separated from the pneumococcus hemotoxin by adsorption with red cells. This removes the hemotoxin and leaves the necrosis-producing principle unaffected. 4. The necrotizing substances obtained from Pneumococcus Types I and II are neutralized by the antiserum prepared with Pneumococcus I.

THE INFLUENCE OF HEATING THE IMMUNIZATION MATERIAL UPON THE ANTIBODY-INVOKING EFFECTIVENESS OF THE TYPE-SPECIFIC AND SPECIES-SPECIFIC ANTIGENS OF TYPE II PNEUMOCOCCUS CELLS

This paper presents an experimental comparison of the effect of heating of the immunization material upon the antibody-invoking effectiveness of the type-specific (SP) and species-specific (P) antigens of Type II pneumococci. Heating of the pneumococcus suspension (vaccine) invariably decreased the production of species-specific antibodies (anti-P) without a comparable effect upon the production of type-specific antibodies (anti-S). For diagnostic typing purposes, the ideal antipneumococcus serum should contain the maximum content of type-specific, and the minimum of species-specific antibody. Our results with forty-one rabbits indicate that the ideal serum from the type-specific standpoint would be obtained by immunization with the heated cells of virulent pneumococci over a comparatively short immunization period; and that the only thing gained by continued immunization or by the use of unheated bacteria at any stage of the immunization, is an increase in the species-specific antibody which is undesireable in sera to be used for diagnostic purposes.

THE PRODUCTION OF PURPURA BY DERIVATIVES OF PNEUMOCOCCUS : II. THE EFFECT OF PNEUMOCOCCUS EXTRACT ON THE BLOOD PLATELETS AND CORPUSCLES

A study has been made of the variation in number of the blood platelets, and the red and white blood cells of white mice injected with pneumococcus extract. The blood platelets were greatly diminished after the injection, the greatest decrease usually occurring after 24 hours. Purpuric lesions usually developed when the number of blood platelets became less than 500,000 per c.mm. Regeneration of the platelets was accomplished by the 4th to the 9th day but there was an overregeneration and the return to normal did not take place until 2 weeks had elapsed. The red cells were also greatly reduced in number, but the rate of their destruction and regeneration was somewhat slower than that of the platelets. The leucocytes were slightly if at all influenced by the pneumococcus extract. Pneumococcus extracts were shown to be thrombolytic and hemolytic. Heat destroyed the activity of both the lysins in vitro. Heated extract produced purpura in mice but did not cause a severe anemia. Extracts adsorbed with either blood platelets or red blood cells showed a marked diminution in their thrombolytic and hemolytic activity in vitro. Such extracts, however, produced purpura as well as severe anemia and thrombopenia in mice.

THE EFFECT OF KILLED BACTERIA ON THE SERUM FERMENTS AND ANTIFERMENT : STUDIES ON FERMENT ACTION. XXVII

1. The intravenous injection of killed organisms is followed by the mobilization of a non-specific protease and lipase; the rapidity and extent of this reaction depend upon the toxicity of the organism and on the resistance of the organism to proteolysis. 2. The temperature and leucocytic curve bear no relation to the ferment changes. 3. The serum antiferment is usually increased after the injection. 4. Of the organisms studied, the typhoid bacilli produced the most marked ferment changes, and the tubercle bacilli the least. 5. The toxicity of the dried organisms cannot depend wholly upon proteolysis in vivo, but must depend in part on the preformed toxic substances liberated on lysis. 6. Serum protease should not be considered as the sole exciter of intoxication through the production of protein split products; it seems possible that its function may in part be one of detoxication.