Efficacy of phage application in modulating raw milk microbiota: Targeting Escherichia coli, Pseudomonas fluorescens, and Lactiplantibacillus plantarum

Abstract

The comprehensive understanding of phages within the food microbiota and their manipulation in a controlled manner is essential for efficient treatment, impacting both microbial quality and technological acceptance of food. In this study, we constructed a simplified core microbiota representing the predominant bacterial groups found in raw milk. Initially, LPP11_FSG phage, which is only susceptible to L. plantarum was isolated and characterized. The burst size and latent period of this phage were 101 PFU/infected cell and 20 min, respectively. Moreover, the phage was heat-sensitive beyond 50 °C but remained stable within a pH range of 4–9. We then examined the efficacy of phage application in broth media containing mono-, dual, and multicultural bacterial and phage groups to minimize pathogenic and spoilage bacteria while controlling beneficial microorganisms in the milk. In the multicultural group, the addition of phages targeting E. coli and P. fluorescens resulted in a reduction of 9.60 and 4.72 logs units, respectively, in the counts of these bacteria compared to the control. Furthermore, the counts of both bacteria remained below 2 logs unit, while the counts of L. plantarum retained a relatively stable level (∼6 logs unit). These optimal results were then investigated in UHT milk at 25 °C for 24 h. In the phage-treated milk groups, and the milk remained stable in terms of acidity (pH 6.48) and microbial quality (total bacterial load remained below 10⁴ CFU/ml), unlike the control group. In the study carried out to determine the stability of milk under cold storage conditions (4 °C), it was found that the growth of psychrotrophs could be controlled during storage without compromising quality. Furthermore, the bacterial counts in the phage-treated groups remained stable at 4 °C for up to 14 days. The findings from this study demonstrate that food microbiota can be modulated in a desired manner using specific phages, and the stability of the new microbiota can be maintained under storage conditions without any increases in bacterial loads.