Contribution à l’étude des souches de bactéries lactiques isolées à partir du lait de vache

Abstract

After isolation and purification, the obtained isolates were subjected to several identification and physiological tests, including Gram staining, catalase and oxidase tests, growth at different temperatures, pH values and NaCl concentrations, fermentation type, heat resistance, and growth on Sherman milk medium. The study was completed by evaluating the antagonistic activity of the isolates against three pathogenic microorganisms and by performing an antibiotic susceptibility test. The results revealed the presence of Gram-positive, catalase-negative lactic acid bacteria that showed good adaptation to various growth conditions and significant inhibitory activity against certain pathogens. The five isolates were classified into two groups: three cocci and two bacilli. All isolates were homofermentative and tolerated temperatures of 37°C and 45°C, 4% NaCl, and pH 9.6. Only one isolate grew at 6.5% NaCl, while two isolates were thermoresistant at 63°C. No isolate grew at pH 4.5. Antimicrobial tests showed that some isolates exhibited inhibitory activity against Candida albicans and Staphylococcus aureus. This study confirms that raw cow's milk is a valuable source of lactic acid bacteria with potential applications in the food and biotechnology industries.