Evaluation of the influence of Lactococcus lactis subp. cremoris bacteriocins used for pre- and post- milking treatment on bovine milk microbiota

In dairy cattle, pre-and post-milking teat disinfections are widely used to reduce or avoid contamination of the milk with pathogens, limit new intra-mammary infections, and prevent the incidence of mastitis. However, these procedures, routinely performed with conventional chemical disinfectants, could unbalance the milk microbial population, affecting also the cheese making properties. The aim of this study was to investigate the use of bacteriocins produced by the Lactococcus lactis subsp. cremoris as evaluable alternative of disinfectants. The experiment involved 20 multiparous dairy cows from the same herd with low somatic cell counts (< 100000 SCC/ml). They were divided into two groups of 10 lactating cows each: (1) control group - a commercial pre-milking and a post-milking disinfectant were applied; (2) treated group -a natural formulation with Lc. lactis subsp. cremoris was used. Milk samples were collected before (T1) and after one (T2), two (T3) and three months (T4) of treatment from two out of the four healthy quarters. The V3-V4 hypervariable regions of the bacterial 16S gene was sequenced in a MiSeq (Illumina) run with 2×250-base paired-end reads. The alpha diversity of the milk microbiome increased significantly (p-values in the range 0.0051 - 0.048) in the treatment group at T2, T3 and T4. Regarding beta-diversity, the milk microbiome showed a statistically significant (p-value = 0.00823) separation both between treatments, as well as timepoints (p-value = 0.0085441) and combining treatments x timepoints (p-value = 0.00464). The bacterial community was dominated by Bacteroidetes (~20%) and Firmicutes (~54%); their levels showed a decrease from T1 to T4, followed by a significant increase of Actinobacteria (~14%) and Proteobacteria (~16%) phyla. Among the genera, 78 resulted significantly different (p-value < 0.05) between the two groups. In conclusion, the use of Lc. lactis subsp. cremoris bacteriocins for pre- and post-dipping seems to have a sizable effect on biodiversity in dairy cow milk microbiome composition. Ack: RABoLa, co-funded by the Region Lombardia D.d.s.21.12.2018 n. 19442.