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

Spontaneous phage resistant mutants- of Lactobacillus helveticus ATCC 15807 were isolated using the lytic phages hv and ATCC 15807-B1. Their genetic d iversity (RAPD fingerprints and DNA extrachromosomal content) and phenotypi c parameters related to their phage resistance capacity (efficiency of plaq uing, phage resistance stability, lysogeny and adsorption rates) were inves tigated to characterize them and to identify potential genetic differences with the parent strain. Phage resistance stability turned out to be a varia ble property among the isolates, but a high level of resistance was exhibit ed by them as quantified by the efficiency of plaquing. Furthermore, a tota l absence of acquired lysogeny was demonstrated. The mutants were completel y or partially unable to bind phages, showing the existence of a widespread resistance mechanism based on adsorption interference. No substantial diff erences in plasmid profiles were observed between the phage resistant varia nts and the sensitive strain. The RAPD fingerprints obtained with three arb itrary primers gave a cluster structure in which all clones appeared to be almost identical (similarity coefficient >75%) to the wild strain. RAPD app ears as a useful tool to rapidly confirm the kindred between parent strains and their phage resistant derivatives. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd, All rights rese rved.