Silent players in ripening: Can phages affect cheese quality?
Résumé
Bacteriophages (phages) infecting lactic acid bacteria (LAB) used in starter cultures have long been recognized by the dairy industry as a leading cause of acidification failures, particularly during cheese production. Collections of LAB-infecting phages exist, and these phages are well characterized. Recent studies have revealed the existence of phages that infect non-acidifying ripening bacteria, although their impact on cheese quality remains poorly understood. It is reasonable to presume that such phages could be responsible for ripening issues in cheeses — such as defects in pigmentation, texture (openings), or flavor — since they can infect strains involved in the development of these organoleptic traits. This study aims to expand knowledge about phages targeting ripening bacteria in order to better anticipate their potential impact on cheese quality. To this end, cheese samples either with or without organoleptic defects were collected. Viral particles were extracted from these samples. The quantity of phages in each cheese was assessed by epifluorescence microscopy. It appeared that the estimated concentrations in virus-like particles (VLP) in cheeses ranged from 9.3 x 106 to 7.4 x 109 VLP/g, and fluctuated depending on the cheesemaking technology. The viral particles preparations were also used to isolate phages, resulting in the creation of the first open-access collection of phages infecting cheese-ripening bacteria. The isolated phages were characterized, notably by transmission electron microscopy for their morphology, as well as for their host range, their genome and infectivity. This collection includes phages targeting strains of Staphylococcus equorum, Corynebacterium casei, Glutamicibacter arilaitensis, and Brevibacterium aurantiacum, all known for their use as ripening cultures. The creation of this collection of phages infecting ripening bacteria paves the way for a better understanding of these viruses. In the next stage of the project, they will be used to assess their impact during cheese ripening.
