Phage-Host Interactions in Commercial Mixed-Strain Dairy Starter Cultures: Practical Significance—A Review

Abstract

Mixed-strain dairy starter cultures are complex ecosystems consisting of undefined mixtures of lactococcal and leuconostoc strains. These starters also often contain lytic bacteriophages that coexist with the bacterial strains in a phage-carrier state. Many of the strains within these cultures have acquired various phage resistance mechanisms that help them survive in the presence of phages in the milk environment. Most lactococcal strains currently used in defined starter systems were originally isolated from mixed-strain starters. Phage resistance mechanisms associated with individual lactococcal strains are studied worldwide; however, few detailed investigations have been conducted to unravel the characteristics and interactions of individual strains and phages coexisting in these complex mixtures. This article presents an overview of mixed-strain starters and discusses the possible mechanisms that contribute to the phage-carrier state and what is known about the characteristics and interactions of bacterial strains and phages residing within mixed-strain starters.