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 concomitant resistance to homologous phage 832-B1 (lysozyme-resistant, PHI-832-B1-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 10(-8)). Some lysozyme-resistant and PHI-832-B1-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.