Inhibition of lactic streptococcus bacteriophage by crystal violet and other agents.

Ninety-nine selected compounds and eleven antibiotic-producing organisms were tested for antiphage activity and host toxicity. A paper disc-agar diffusion method was used for primary screening and quantitative methods were employed for confirmatory investigation. Most of the agents tested, although previously reported as inhibitory to one or more other virus-host systems, did not selectively prevent multiplication of lactic streptococcus bacteriophage. Several compounds which prevented mass lysis were extremely toxic to host bacteria. Crystal violet suppressed growth of two phage strains at a level (1.0 x 10(-7)M) which permitted normal growth of the host cells. Failure of crystal violet to prevent multiplication of many phage strains suggested possible variations in the multiplication mechanisms of different strains of virus. Virustatic levels of crystal violet did not destroy unadsorbed virus, reduce adsorption, or prevent invasion; increase of virus was reduced in one-step growth experiments; mass lysis was prevented or delayed in long time experiments. Addition and removal of crystal violet at various intervals during the latent period resulted in virus yields directly related to the portion of the latent period during which no dye was present. Duration of the latent period was unaffected. Single burst experiments indicated that the yield of plaque-forming particles per infected bacterium was reduced; the proportion of infected bacteria giving rise to active progeny did not appear to be influenced to a significant degree. Crystal violet apparently interferes with intracellular multiplication of the virus, possibly by combination of the dye with phage DNA or fractions thereof at some critical stage in the incorporation of DNA into the virus particle.