Lysogeny in encapsulated and nontypable strains of Haemophilus influenzae

Encapsulated and nontypable Haemophilus influenzae isolates recovered from pediatric patients and healthy children are examined for their ability to lyse and to release phage after mitomycin C induction. Lysis occurred in 16 out of 58 isolates tested for lysogeny. The serotype b capsule of H. influenzae does not exhibit an inhibitory effect on either cell lysis or the ability of the cells to become lysogenized. Electron microscopic examination revealed the presence of tailed particles in 11 lysates. The tailed particles belong to two morphological groups (A and B) according to the classification of Bradley. None of the phages was able to produce plaques when tested on a large number of strains. However, five lysates exhibited killing properties involving several nontypable H. influenzae strains. This effect sedimented with the bacteriophage after centrifugation. All the phages recovered from H. influenzae isolates in this study appeared to be genetically defective.