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Title: Hemolysins of Staphylococcus
Author: Wiseman, Gordon Marcy
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1974
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On the basis of chemical and immunologic evidence, most investigators now believe that Staphylococcus aureus may produce at least four distinct hemolytic proteins. These have been designated alpha, beta, gamma and delta hemolysins. The function of these hemolysins in the economy of the Staphylococcus has not been fully elucidated, but some detail is available with regard to their nature and in vitro mode of action. Agreement on the properties of the four hemolysins has nevertheless been difficult to obtain because of wide variation in methods of purification and choice of strains. Moreover, confusion has existed in many laboratories with regard to the identity of the hemolysin under study. Recent work has permitted a number of generalizations to be made. Amino acid analyses of the hemolysins have revealed that no unusual acids are present. All hemolysins are soluble in water although of somewhat varying stability, and when pure, no carbohydrate, lipid or other accessory materials have been detected. It is also fairly well-established that at least three, the alpha, beta and delta hemolysins, are basic proteins the isoelectric points of which are in the range of 8.5-9.6. Apart from the delta lysin, their molecular weights are less than 100,000 daltons, the majority of observations being in the range of 20,000-50,000 daltons. The mode of action of the hemolysins has generated some debate, but it is accepted that the beta lysin is an enzyme which degrades sphingomyelin, a phospho¬ lipid widely distributed in cell membranes. The view that the delta lysin is also a phospholipase which attacks phosphatidyl-inositol has frequently been challenged but it must be pointed out that until very recently, workers have not clearly distinguished between gamma and delta lysins. The precise mode of action of the latter is unknown but contemporary work indicates that although gamma lysin has no action on sphingomyelin, phosphatidylinositol or other comnon phospholipids, nitrogen and phosphorus are released from erythrocyte membranes treated with the lysin. Furthermore, it can be shown that hemolysis is inhibited by the membranes when these are added to lysin-red cell suspensions, and that phospholipids extracted from human erythrocytes competitively inhibit the lytic reaction. The mode of action of the alpha lysin has also been elusive but considerable evidence has been compiled which indicates that the lysin is produced by the Staphylococcus as an inactive protease which degrades membranes that contain an activating protease. It has been observed that hemolytic sensitivity of erythrocyte species to alpha lysin is directly correlated with the level of activator present on the membranes. Apart from this, several investigators have demonstrated that the lysin has surface activity, but it is difficult to reconcile the two points of view. No agreement has been reached on the biological properties of the beta, ganma and delta hemolysins in view of the difficulties of purification and definition. Most workers agree, however, that the alpha lysin kills mice and rabbits in doses at the microgram level (although it is thousands of times less toxic than botulinum or tetanus toxins) and that it causes tissue necrosis when injected into the skin. In vivo production of the hemolysins in animals and man has been demonstrated by the detection of circulating antibody in normal and diseased subjects, but until the present, controversy existed over whether the delta lysin was in fact capable of eliciting an antibody response, since serum lipoproteins inhibited its lytic activity. The use of homogeneous preparations of the lysin and purified antibody has conclusively demonstrated its immunogenicity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available