SELECTION OF SOME BACTERIOPHAGE-RESISTANT AND LYSOZYME-RESISTANT VARIANTS OF LACTOBACILLUS-HELVETICUS CNRZ 892

Different strains of Lactobacillus helveticus were tested for lysozyme resistance, and one out of three (L. helveticus CNRZ 892) showed a co ncomitant resistance to homologous phage 832-B1 (lysozyme-resistant, P HI-832-B1-resistant). The mechanism of phage resistance acquisition se emed to be related to a decreased phage adsorption as well as to a sha rp decrease in plaque-forming ability (less than 10(-8)). Some lysozym e-resistant and PHI-832-B1-resistant derivatives of strain CNRZ 892 lo st the ability to ferment galactose and trehalose and showed loss and rearrangement of plasmids. Chemical treatments of L. helveticus CNRZ 8 92 and some phage-resistant derivatives showed that the accessibility of the phage receptor present in the cell wall of some mutants may be masked by a surface component that was absent in the original strain. The results suggested the possibility of using lysozyme as a selective agent to isolate phage-resistant derivatives from a population of L. helveticus CNRZ 892 sensitive to both lysozyme and bacteriophage.