Characterization of Lactobacillus helveticus phage resistant mutants by RAPD fingerprints and phenotypic parameters

Abstract

Spontaneous phage resistant mutants of Lactobacillus helveticus ATCC 15807 were isolated using the lytic phages hv and ATCC 15807-B1. Their genetic diversity (RAPD fingerprints and DNA extrachromosomal content) and phenotypic parameters related to their phage resistance capacity (efficiency of plaquing, phage resistance stability, lysogeny and adsorption rates) were investigated to characterize them and to identify potential genetic differences with the parent strain. Phage resistance stability turned out to be a variable property among the isolates, but a high level of resistance was exhibited by them as quantified by the efficiency of plaquing. Furthermore, a total absence of acquired lysogeny was demonstrated. The mutants were completely or partially unable to bind phages, showing the existence of a widespread resistance mechanism based on adsorption interference. No substantial differences in plasmid profiles were observed between the phage resistant variants and the sensitive strain. The RAPD fingerprints obtained with three arbitrary primers gave a cluster structure in which all clones appeared to be almost identical (similarity coefficient >75%) to the wild strain. RAPD appears as a useful tool to rapidly confirm the kindred between parent strains and their phage resistant derivatives.