Study of Alpha and Beta Units of an Anti-Paratyphoid Bacteriophage.

Abstract

Under the influence of a fresh, sewage filtrate we isolated a lytic agent for an old laboratory strain of B. paratyphosus A, in the S cyclostage. This filtrate, which was first active in F₃, was enhanced to a high titer by alternate feeding and filtration in series. When tested by the plate method against the homologous culture there first appeared only large plaques. Later (F₆), the filtrate gave small plaques in addition to the large. With continued propagation there was a tendency for the large plaques to be replaced by the small.

The large lytic areas possessed an average diameter of 6 to 7 mm. when mature. As a rule, there were no areas of intermediate size. A few that measured from 3 to 4 mm. possessed the chief characteristics of the large plaques, and on further propagation they always reproduced the large area type. The small lytic areas were sharp and clearcut, while the large areas were usually surrounded by a hazy zone of imperfectly lysed culture. As a rule the principle determining the large areas permitted the appearance of a relatively larger number of secondary, resistant colonies than did the small-area principle. Frequently, under conditions of crowding, the large areas enclosed one or more of the small. In this case the latter were especially distinct if they happened to lie in the marginal zone of the large areas; for, here, the small areas completed the lysis which had been left imperfect by the large areas.

Separate, pure line, lytic filtrates were prepared through isolations performed upon discrete large and small areas respectively, and these filtrates were built up to a moderately high titer by alternate feeding and filtration in series.