Biomedical subjects
K C Watson
Publications and source records attributed to K C Watson.
Laboratory and clinical investigation of recovery of Salmonella typhi from blood.
An experimental study was undertaken of isolation of Salmonella typhi from artificially infected whole blood and blood clot prepared either with small numbers of freshly isolated strains or with the S. typhi Ty2 strain. Results showed that 8 ml of whole blood required a minimum of 50 ml of bile salt broth to dilute the bactericidal effect of the serum. However, the isolation rate for recovery in 210 cases of enteric fever was only 64% when 50 ml of medium was used, as compared to 92% recovery from blood clot from the same group incubated in streptokinase bile salt broth. This probably reflects a very low grade bacteremia in many of the patients. Further investigation showed that, ideally, between 150 and 200 ml of medium is required for satisfactory whole-blood culture. Both the experimental study of artificially infected clots and recovery rates from patients indicate that rapid clot dissolution with streptokinase is preferable to whole-blood culture; this experience has been amply confirmed by almost 5,000 cases over a 20-year period. A 15-ml volume of bile salt broth with 100 U of streptokinase is adequate for the clot from 8 ml of blood, and savings on media and incubator space have considerable cost benefits in developing countries.
Polyene antibiotics in assessing significance of antistreptolysin O activity.
Antistreptolysin O activity in serum is due either to antibody or to altered lipoprotein molecules. The latter can be inhibited by performing antistreptolysin tests using a polyene antibiotic such as amphotericin B as diluent.
Antistreptolysin activity in staphylococcal infection.
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Studies on antistreptolysin O activity generated in serum by microorganisms.
An antistreptolysin factor (ASF) was generated in normal human serum by the growth of Staph, aureus and Pseud, aeruginosa. Alpha toxin producing strains of the former were usually positive but activity was not restricted to such strains. Positive strains produce cholesterol esterase which was obtained from DEAE-cellulose column fractions of 18 h broth cultures. Antistreptolysin factor develops slowly in serum, being maximal between the 5th and 10th days and is associated with alterations and disappearance of beta lipoproteins on gel electrophoresis. Activity also appeared in beta lipoproteins precipitated from normal serum with dextran sulphate and redissolved in nutrient broth before inoculation with Staph, aureus. The slow appearance of antistreptolysin activity in serum appears to be due to an esterase inhibitor which is present in high concentrations in some sera. Activity is also modified by the production of a staphylococcal fraction capable of binding to the antistreptolysin factor and reducing its activity. It is suggested that antistreptolysin factor which can be demonstrated in small amounts in normal human serum represents a readily available non-specific defence mechanism capable of binding to certain bacterial products and possible to other foreign protein molecules.
Cholesterol esterase activity in body fluids.
Antistreptolysin O activity (greater than or equal to 200 Todd units/ml) was found in 20% of 25 ascitic fluids, 20% of 55 pleural fluids and 37-5% of 56 joint fluids. These levels are not due to antibody but to the cholesterol moiety of altered beta-lipoproteins. The activity is precipitable with 10% dextran sulphate. Incubation of mixtures of fluids with titres less than 200 and normal human serum generated eight-fold or greater rises in antistreptolysin titres. This results from the activity of cholesterol esterase in the fluid acting on the beta-lipoprotein of the serum and activity was noted in 90% of ascitic fluids, 59% of pleural fluids and 54% of joint fluids. However, mixtures showing no such rise probably also contain esterase, the failure to demonstrate antistreptolysin activity being due to equilibration of ester derived cholesterol with sub-fractions of high density and very low density lipoproteins.
Letter: Cholesterol-binding capacity and atherogenesis.
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Letter: Laboratory diagnosis of typhoid fever.
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Functional role of cholesterol in infection and autoimmunity.
Cholesterol binds to streptolysin O and related bacterial toxins. In normal serum, only a fraction of the cholesterol attached to lipoprotein is available for binding, probably as a cholesterol-peptide complex formed during catabolic breakdown of the lipoprotein. Cholesterol esterase produced by certain organisms--e.g., Staphylococcus pyogenes and Pseudomonas oeruginosa--augments this fraction both in vitro and in vivo. Endogenous esterase similarly increases the amount of cholesterol-peptide complex, a mechanism which may be activated as a feedback process following binding of toxin to the cholesterol component of the complex. These complexes will thus supply a readily available means of binding bacterial toxins before antibody formation begins; Cholesterol-peptide complexes, either alone or modified by binding to toxin, may function as autoantigens. It is postulated that immune complexes so formed may be involved in atherosclerosis either by directly damaging vessels walls or by cross-reaction of antibody with cell-membrane-bound lipoproteins which equilibrate with plasma-lipoproteins.
Partial characterisation of an inhibitor of streptolysin O produced by bacterial growth in serum.
An inhibitor of streptolysin O is generated in human and animal sera by the growth of certain organisms. The ability to do this occurs most often in Pseudomonas aeruginosa and Staphylococcus aureus (in 90% and 86% of strains respectively), but in only 32% of Staph. epidermidis strains. The inhibitor is not formed in broth. The effect appears slowly on incubation, with maximum activity after 4-7 days. Evidence suggests that two enzymes are involved, an esterase which splits ester-bound cholesterol and a proteolytic enzyme which partially hydrolyses lipoprotein, resulting in cholesterol remaining attached to protein or polypeptide fractions but with some alteration of its spatial configuration such that it is now capable of attaching to streptolysin O. The inhibitory factor appears to prevent streptolysin becoming attached to cholesterol receptor sites on the erythrocyte membrane. Removal of the precursor from serum with magnesium carbonate suggests that low-density lipoproteins may be the precursor of the inhibitor.