Études phénotypiques et génotypiques des bactéries lactiques isolées du lait de vache cru

Abstract

Raw cow’s milk represents a complex ecosystem and a rich natural reservoir of autochthonous lactic acid bacteria with significant potential for food biotechnology. The primary objective of this study was to isolate, phenotypically characterize, and genotypically identify the indigenous lactic flora from raw cow’s milk collected in the Mazagran region (Mostaganem, Algeria). Physico-chemical analyses of the collected milk samples confirmed high hygienic quality and freshness, with pH values ranging from 6.5 to 6.7. Isolation on MRS medium led to the selection of six representative strains (S1 to S6), all of which were Gram-positive and catalase-negative. Comprehensive phenotypic characterization including cell morphology, physiological tolerance to temperature, pH, and NaCl, alongside carbohydrate fermentation profiling allowed the assignment of coccoid isolates (S1 to S4) to the genus Enterococcus (E. faecium and E. faecalis), whereas rod-shaped isolates (S5 and S6) were linked to the lactobacilli group. To refine and achieve definitive taxonomic identification at the genomic level, molecular fingerprinting using (GTG)₅-PCR was performed. Electrophoretic pattern analysis and dendrogram clustering successfully identified isolate G7 as Lactiplantibacillus plantarum (ATCC 8014 reference strain) and isolates G1, G2, and G5 as Limosilactobacillus fermentum (ATCC 9338 reference strain). The high genetic similarity among G1, G2, and G5 indicates a shared ecological origin. Overall, this study demonstrates the complementarity of phenotypic and molecular methods in evaluating raw milk microbial diversity and highlights the technological value of local lactic acid strains.