Starter Culture Rotation for Bacteriophage Control in Dairy Production

Abstract

Bacteriophages remain a major cause of fermentation failures in cheese and fermented dairy production. No starter culture, even those with high phage resistance, can be used indefinitely due to the evolutionary plasticity of viruses. Phage monitoring (such as qPCR or the Delvo®Phage test kit) is an essential risk management tool. This article describes how phages overcome bacterial defense systems (receptor modification, CRISPR-Cas evasion, anti-CRISPR proteins, and abortive infection (Abi) systems), providing a scientific rationale for obligatory culture rotation. While Western researchers agree upon flexible rotation schedules, Russian and Belarusian practices stipulate limiting subcultures to 5–7 passages. The article contains practical rotation strategies for both direct vat set (DVS) starters and traditional subcultured starters. It includes recommendations for rotation frequency (ranging from 2–3 days to several weeks), commercial rotation series, and a step-by-step algorithm for dairy plants that covers everything from phage load assessment and rotation strategy selection to sanitation measures and personnel training.