Effects of antibiotics on induction, viability, and reversion potential of L-forms of Haemophilus influenzae.

L-form variants of Haemophilus influenzae were found to be more susceptible than their parent bacilli to streptomycin, kanamycin, tetracycline, erythromycin, and chloramphenicol if L-form inducer, penicillin, was present. This greater susceptibility was defined as the bactericidal effect for the variant forms of a concentration of antibiotic that is lower than but approximates the level bacteriostatic for the parents. In the absence of penicillin, reversion to and growth as bacilli occurred, although kanamycin, chloramphenicol, and erythromycin were lethal for round-body inocula on antibiotic reversion media in a few instances. The development of round bodies from bacillary inocula on induction medium was inhibited by bacteriostatic concentrations of chloramphenicol or tetracycline. The bacilli survived for 72 hr or more, whereas round bodies were dead within 24 hr.