Typing of paratyphoid b bacilli by means of VI bacteriophage

Abstract

Anti-Vi bacteriophages that act specifically on Bact. paratyphosum B are described. Anti-O bacteriophages, on the other hand, attack strains belonging to many diverse Salmonella species. Anti-Vi phages of Bact. paratyphosum B can be adapted to develop a high degree of specificity for particular strains, whereas anti-O phages are incapable of such adaptation. Four separate and distinct Vi-phage types and subtypes of Bact. paratyphosum B have been identified so far, and a method of typing strains of paratyphoid B bacilli has been developed similar to that which was first devised by Craigie and Yen for the typing of typhoid bacilli. Of 714 strains isolated from patients or carriers in Great Britain only 50 (7%) could not be typed by means of the available four Vi-type phages. The larger outbreaks of the disease in 1941 were found to have been caused by Type 1 strains. The significance of paratyphoid-B Vi-phage types is the same as that of typhoid Vi-phage types. The typing of paratyphoid B strains isolated from sporadic cases or outbreaks is a valuable epidemiological weapon and is certain to be widely applied in the future. © 1943, British Medical Journal Publishing Group. All rights reserved.