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Coordinate Effects of Electrolyte and Antibody on the Infectivity of Bacteriophage

From the Department of Bacteriology and Immunology, Washington University School of Medicine, St. Louis, Missouri

Abstract

A variety of small plaque phages acting on Escherichia, Salmonella, Eberthella, and Shigella are markedly dependent on the presence of univalent cations for their infectivity. Other phages show a variable, usually lesser, dependence on salt. A large-plaque coliphage proved to be relatively independent of salt. Two salt-sensitive coliphages were studied in detail. With these the effect of salt is to increase the rate of sorption to bacteria, but this effect is not the sole explanation of the increased infectivity. Phage adsorbed to bacteria may or may not initiate regeneration, apparently depending on which of two alternative adsorptive mechanisms is utilized. The one, which predominates in the presence of salt, constitutes infection; the other, which predominates in the absence of salt, has no effect on the bacteria. In general, both types of adsorption occur, and only a variable fraction of the bacteria which have absorbed phage are actually infected.

Phage particles that have been allowed to react with amounts of antibody too small to effect neutralization, exhibit properties markedly different from those of the native phage. This alteration can be brought about without significant neutralization, and therefore applies to the entire population. The sensitized active particles are more infectious at low salt concentrations, and are more rapidly adsorbed to bacteria, than the original phage. The effect of antibody on adsorption is a predominating influence on the form of the neutralization curve when the conditions of enumeration are unfavorable, but not when they are optimal.

The pH of the phage-bacterium mixture does not appreciably affect the rate of adsorption in the absence of electrolyte.

The experiments are discussed in relation to the proper interpretation of virus neutralization tests in general, and in particular with reference to conclusions which have been drawn regarding the reversibility of the virus-antivirus reaction, and the question of the heterogeneity of the viral population.

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