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Investigations of the Effect of Some Antibacterial Agents on a Bacteriophage

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Investigations of the Effect of Some Antibacterial Agents on a Bacteriophage 1. INVESTIGATIONS OF THE EFFECT OF SOME ANTIBACTERIAL AGENTS ON A BACTERIOPHAGE. A THESIS submitted by WILLIAM ROBERT LAING BROWN for the degree of DOCTOR OF PHILOSOPHY in the UNIVERSITY OF LONDON. School of Pharmacy, University of London. April 1962. 2. ABSTRACT. The effects on coliphage T6r of 11 commonly used chemical antibacterial agents have been examined. The effect of the agents on the multiplication of the phage was shown by their effect on the mass lysis of fluid cultures of the host by the phage. Only aminacrine hydrochloride and sodium lauryl sulphate showed significant inhibition of the growth of the phage at concentrations below those inhibiting the host. For the examination of the effect of the agents on free phage particles, a method of assessment giving precise inactivation time estimates has been applied and two methods of interpreting the results have been compared. Large differences have been shown in the effectiveness of different antibacterial agents in inactivating the free phage. The effect on the inactivation time of changes in concentration of the antibacterial agent has been examined for five of the agents and the regression between log inactivation time and log concentration has been shown to be linear. The dilution coefficients for these agents fell into two distinct groups, those for ohioramine T and formaldehyde (about 2 and 3 respectively) being very much smaller than those for crystal violet, cetrimide and phenol (about 11,13 and 15 respectively). It has been postulated that this difference in dilution coefficients indicates different mechanisms of inactivation between the two groups and the possible nature of the mechanisms has been discussed. Methods of cultivation of the phage and its stability under different conditions of storage have been investigated. A method of plaque counting by surface drop plating has been developed and its reproducibility examined. 3. CONTENTS. Title 1 Abstract 2 Contents 3 Acknowledgements 6 PART I. INTRODUCTION Definitions 8 Inhibition of the interaction of phage and host 9 Inactivation of free bacteriophage 13 Assessing the inactivation of free phage 16 Counting methods 16 Extinction methods 17 Phage extinction methods 18 Bacterial extinction methods 20 The viricidal activity of specific antibacterial agents on phage 23 Chlorine compounds 23 Formaldehyde 25 Medicinal dyes 27 Triphenylmethane dyes 27 Acridine derivatives 28 Mercury Compounds 29 Phenol and its derivatives 31 Surface active agents 33 Quaternary ammonium compounds 33 Anionic surface active agents 34 Object of present work 35 4. PART II. EXPERIMENTAL TECHNIQUES AND RESULTS. A. Apparatus 37 1. Dropping pipettes 37 2. Volumetric apparatus 39 3. Automatic tilt measures 39 Miscellaneous containers 40 B. Materials 42 1. Water 42 2. Media 42 3. Antibacterial agents 43 C. The Bacterial Host 46 1. Characters 46 2. Maintenance of cultures 47 3. Stability of characters 47 4.. Viability of cultures 48 D. The Bacteriophage 51 1. Cultural characteristics 51 2. Counting of phage particles 52 3. Preparation of phage stocks 71 4. Storage of phage stocks 79 E. Inhibition of the action of the phage on its host 81 1. The effect of inocula size on the rate of action of the phage on its host. 81 2. The effect of antibacterial agents on the action of the phage on its host 84 3. The effect of size of phage inoculum on the rate of lysis in the presence of antibacterial agents. 90 5. F. Inactivation of free phage by antibacterial agarlia 94 1. Method of evaluation 94 2. Reproducibility of the method 98 3. Estimation of the Mean Single Survivor Time 98 h- Relation of Mean Inactivation Time to Mean Single Survivor Time 110 5. Two factors affecting the reproducibility of the 113 Mean Inactivation Time 6. The systematic examination of the antibacterial agents 116 PART III. DISCUSSION . The Bacteriophage 128 Phage plaque counting method 128 Cultivation of phage 129 Storage of phage 130 Inhibition of the action of the phage on its host 130 Inactivation of free phage 135 The method of evaluation 135 The precision and reproducibility of the method 139 The Mean Single Survivor Time 140 The relation of Mean Inactivation Time to the Mean Single Survivor Time. 141 The systematic examination of the antibacterial agents 1)i2 Phage reactions and other viruses 149 Suggestions for further work. 151 Bibliography. 151_ 6. ACKNOWLEDGEMENTS. I wish to record my gratitude to Dr. A.M. Cook for first suggesting the subject of this thesis and for his helpful and enthusiastic direction of the work presented here. I am also grateful for the technical assistance of Mr. A. Edwards and his staff in preparing the apparatus and materials used. 7. PART I. INTRODUCTION. J. DEFINITIONS. The term antibacterial agent may be used to describe any agent, physical or chemical, which inhibits the growth of or kills bacteria. Heat, sonic vibration, white light, ultraviolet and ionising radiations may all be classed as physical antibacterial agents while the term chemical antibacterial agent may be used to describe those chemicals having a bacteriostatic or bactericidal action and referred to variously as disinfectants, antiseptics and germicides. The investigations which are the subject of this thesis were concerned with examining the effect of chemical antibacterial agents on a baoteriophage and the term "antibacterial agent" will be used throughout the thesis as meaning this type of agent. The agents considered have been further limited to include only those which belong to the classes of compounds commonly used as disinfectants or antiseptics, namely chlorine compounds, formaldehyde, medicinal dyes, mercury compounds, phenol and its derivatives and surface active agents. The antibiotics and other chemotherapeutic agents have been largely excluded. The study of the action of antibacterial agents on bacteriophages has two main aspects. The first is the action of the agents on extracellOrm phages and the second is the interaction of phages and their bacterial hosts in the presence of the agents. The present work has been primarily concerned with the former aspect but any such study must include a consideration of the latter. This arises because the examination of antibacterial agents for possible viricidal activity 90 requires a clear distinction to be made between viristatic and viricidal effects. Tests for virioidal action. must therefore be so designed as to ensure that conditions are provided in which any phage particle surviving exposure to the agent can subsequently multiply, INHIBITION OF THE INTERACTION OF PHAGE AND HOST. Inhibition of the growth of phages by the presence of an antibacterial agent may result from inhibition of the growth of both the bacterial host and the phage. Alternatively, phage production may be arrested by a selective inhibition of phage growth with no effect on the growth of the host. Several surveys have been undertaken in which large numbers of substances have been examined for possible selective phage inhibitory action in the hope that compounds showing this action may have some application in the development of chemotherapeutic agents for viral infections in man. Notable amongst these surveys are those carried out by Asheshov and his co—workers (Hall et al, 1951; Asheshov et al , 1950, Bourke et a] (1252), Boyd and Bradley (1951), Chantrill et al (1952) Dickinson (1948), Graham and Nelson (1954), Mills (1955) and Wooley et a] (1952). From all these surveys the same general picture emerges; that, of thelundreds of compounds tested, the majority inhibit both bacteria and phage and only a very few show any selective phage inhibitory action. Of these the majority have proved to have no application as chemotherapeutic agents against animal viruses. In investigating the mechanism of selective inhibitors of phage growth 10. a wide variety of techniques, some relatively oomplex, are required to show the effect of the inhibitor on all or some stages of miltiplication, A useful, indication of whether or not a compound possesses phage-speoifio inhibitory activity can, however, be obtained by the relatively simple procedure of examining its ability to inhibit visible or mass lysis of a bacterial culture infected with phage. In preliminary screening programmes this effect is conveniently shown on a qualitative basis using phage cultures on solid media the agent under test being localised in the medium by use of the cup-plate and filter-paper disc teohnique (Jones and Schatz, 1946; Ball et a]., 1951; Asheshov et al, 1954). This type of procedure must then be followed by a quantitative determination of the concentration of phage inhibitor whioh will prevent mass lysis in fluid culture of the phage without affecting the growth of the host, the progress of lysis being followed by estimation of the turbidity of the culture. Finally, if the agent shows promise, the detailed examination already referred to may be undertaken using techniques such as the single-step growth curve (F1iis and DelbrUck, 1939; DelbrUckand Luria, 1949) or electronmicrographio and radiochemical examinations. A detailed examination of the mode of aotion of the few selective phage inhibitors known is outside the scope of the present work and the subject has been extensively reviewed by Gots (1959). Two examples of selective phage inhibition are, however, of particklar interest in the investigations to be reported here. The first example is the action of the acridine derivatives. Modern interest in the action of these compounds on phage was stimulated by 11. the demonstration by Fitzgerald and Babbit (1946) that a number of acridines, in sub-bacteriostatic concentrations, inhibited the lysis of Escherichia coli infected with phage. From the large number of reports on the subject subsequently published (cots, 1959),it became clear that - (a)not all acridines had a selective action in inhibiting all phages, (b) aoridines have little effect on free, mature phage00 (c)the inhibitory action of acridines can be reversed by the addition of ribonucleio acid (RNA) or desoxyribonuoleic acid (DNA), (d)the acridines act by blocking the final steps in the maturation of the phage particles.
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