Host cell reactivation was induced by oxygen in Bacteroides fragilis . Chloramphenicol inhibited the induction of host cell reactivation. DNA and protein syntheses were not inhibited during oxygen-induced host cell reactivation.

Reactivation of UV‐irradiated phage b‐1 was induced by H2O2 and UV in Bacteroides fragilis. The characteristics of H2O2 and UV induced phage reactivation differ from a previously reported oxygen induced reactivation system. The survival of B. fragilis cells after UV irradiation was also increased by pretreatment with H2O2. DNA synthesis was not inhibited in the host cells exposed to H2O2 concentrations which induced phage reactivation. The pattern of DNA degradation and synthesis after UV irradiation with and without H2O2 differed from the effect of O2 on DNA synthesis in irradiated B. fragilis cells.

The survival of Bacteroides fragilis cells after far-ultraviolet irradiation under anaerobic and aerobic conditions and the liquid holding recovery under aerobic conditions were not affected by peroxide or quenchers of toxic oxygen derivatives.