Changes in bacterial populations in refrigerated raw milk collected from a semi-arid area of Algeria

Abstract

Most of the studies on milk microbiota have been performed on cows’ milk from animals reared in temperate and humid areas. In this work, changes in the bacterial consortium of refrigerated raw milk collected from cows grazed in a semi-arid area of Algeria were studied during 21 days of refrigerated storage. Twenty bacterial morpho-physiotypes were selected among 150 isolates from milk at different times over storage and identified by partial 16S rRNA gene sequencing. The dominant bacterial populations were characterized by a few species. Stenotrophomonas rhizophila, S. maltophilia and Chryseobacterium indologenes were predominant during the first 7 days, Lactobacillus pentosus and L. plantarum were isolated only after the 10th day, while Acinetobacter spp. was isolated at the end of storage. Compared to the current literature on milk from temperate zones, sluggish and incomplete microbial growth was observed with a long incubation phase ranging from 6.7 to 10.5 days and a maximum growth not exceeding 5.3 log colony-forming units (CFU) · mL−1. The composition of milk microbiota and its evolution over refrigeration suggest a bio-geographical characterization due to environmental factors. In particular, the possible presence of antimicrobial molecules coming from plants grazed in the semi-arid zone around the farm may account for the presence of selected microbial species and the extended milk shelf-life. Despite this being a preliminary work, these results encourage the use of arid herbs in animal feed and motivate scientists to focus their efforts on the study of biochemical composition of plants from arid areas and their antimicrobial activity.