Technological performance of spontaneous phage-resistant derivatives of Leuconostoc mesenteroides and Leuconostoc pseudomesenteroides during milk fermentation

A total of 142 presumptive phage-resistant derivatives were isolated from six commercial phage-sensitive Leuconostoc mesenteroides and Leuconostoc pseudomesenteroides strains, using six phages either individually or in combination (cocktail). Genetic diversity, efficiency of plaquing (EOP), phage-resistance stability, lysogeny, adsorption rates and technological performance were determined for the 89 confirmed phage-resistant variants. Derivatives showed very low EOP values (<10−10) and high stability of phage-resistance phenotype. Some mutants showed low adsorption rates (10-42%) thus indicating adsorption interferences. Additional resistance mechanisms (operative at later stages) were suggested for mutants revealing high phage adsorption rates. A good performance during milk fermentation and the subsequent refrigerated storage in the presence of phages was demonstrated for four mutants, selected on the basis of their stability and low or null phage adsorption. These phage-resistant variants could be used in industrial rotation schemes when commercial strains become sensitive to phages present in the environment.