Phenotypic Alterations Associated with the Bacteriophage Carrier State of Shigella dysenteriae

Abstract

Shigella dysenteriae strain 136-R 4 is lactose-negative (Lac- Mann-) and is sensitive to bacteriophage T7. Carrier clones of strain R4, isolated from colony that had survived lysis by phage T7, were found to maintain their association with phage T7 through as many as 50 consecutive single-colony isolations. All carrier cultures, so-called pseudo-lysogenic strains, give lactose-positive and mannitol-positive (Lac+Mann+) reactions. Passage of Lac+ Mann+ bacteria through media containing antiserum directed against phage T7 resulted in the complete elimination of phage T7 and in a change back to Lac- Mann-. Biochemical, genetic and immunochemical evidence indicates that the change from Lac-Mann- to Lac+ Mann+ is the result of a phage-controlled alteration in the phenotype of Shigella dysenteriae. This dysentery bacillus is cryptic with respect to the expression of Lac+ Mann+ and the crypticity is attributable to surface structures, which are probably not a part of the Y or permease system. Under appropriate conditions decrypti-fication may be brought about by phage-associated endolysin. Similar phenomena were observed in carrier strains of certain other members of the Enterobacteriaceae.