Selection of Some Bacteriophage 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 concomitant resistance to homologous phage 832-B1 (lysozyme-resistant, ~832-B I-resistant).The mechanism of phage resistance acquisition seemed to be related to a decreased phage adsorption as well as to a sharp decrease in plaque-forming ability (less than 1(}-8).Some lysozymeresistant and ~832-Bl-resistant derivatives of strain CNRZ 892 lost the ability to ferment galactose and trehalose and showed loss and rearrangement of plasmids.Chemical treatments of L. helveticus CNRZ 892 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.