Phenotypic Alterations Associated with the Bacteriophage Carrier State of Shigella dysenteriae

SUMMARY: Shigella dysenteriae strain 136-R4 is lactose-negative, mannitol-negative (Lac-Mann-) and is sensitive to bacteriophage T7. Carrier clones of strain R4 (contaminated with T7) were found to maintain their association with phage T7 through as many as fifty consecutive single-colony isolations (from an ancestral colony which had survived lysis by phage T7). All carrier cultures (so-called pseudo-lysogenic strains) were found to be lactose-positive and mannitol-positive (Lac+ Mann+). Passage of Lac+ Mann+ bacteria through media containing antiserum directed against phage T7 resulted in a change back to Lac- Mann- and in the complete elimination of phage T7.

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 decryptification may be brought about by phage-associated endolysin. Similar phenomena were observed in carrier strains of certain other members of the Enterobacteriaceae.