Effect of Chloramphenicol on Host-Bacteriophage Relationships in the Lactic Streptococci

Chloramphenicol (CM)-resistant mutants of Streptococcus lactis strain ML3 were obtained either as a consequence of continuous transfer of the bacteria in broth containing increasing amounts of CM or by selecting for high-level resistant derivatives after mutagenic treatment of the bacteria. Some CM-resistant cells ob- tained by the first method were also resistant to the homologous bacteriophage. Cells trained to grow in the presence of CM developed resistance to some heterologous attacking phages but not to phage mls. Mutants selected for phage resistance were not resistant to CM. There appear to be two different loci for CM resistance on the bacterial chromosome: the one for high-level resistance is associated with the phage-resistance locus and the other is independent of it. A concentration of CM (280 ,g/ml) that was bacteriostatic for ML3 inhibited the intracellular growth of ml3 phage in strain ML3-CMrI, which had been trained to grow in the presence of that CM concentration, despite the fact that cells of this strain were not phage-resistant per se. The drug had no direct virucidal action and did not prevent adsorp- tion to or penetration of phage into the bacterium. Lysogenization did not occur. synthesis either involving acid at an early stage or the phage coat at a later one.