Identification of Lactobacillus strains from human mother milk and cottage cheese revealed potential probiotic properties with enzymatic activity
Bacterial isolation and culture media
Lactic acid bacteria were isolated from human mother milk, and cottage cheese, yogurt, boiled and unboiled milk, and pickles; all collected from different local dairy product markets.
Informed consents were obtained from all recruited individuals. Also, ethical approval for the study was obtained from the local ethical committee of the Faculty of Science, University of Alexandria, Egypt. All methods were carried out in accordance with relevant guidelines and regulations.
Sterile bottles and bags were used to collect samples, to be stored in an ice box until transferred to laboratory for further examinations. One milliliter of each sample was serially diluted using sterile saline solution and spread over selective medium: De Mann, Rogosa Sharpe (MRS) with the following composition (g/l): peptone, 10; beef extract, 10; yeast extract, 5; glucose, 20; tween 80, 1; ammonium citrate, 2; sodium acetate, 5; magnesium sulphate, 0.10; di-potassium phosphate, 2 and agar, 10. The medium pH was adjusted at 6.2 ± 0.2, and then incubated at 37 °C for 24 h9. For obtaining pure culture, separate and morphologically different colonies were isolated and, immediately, sub-cultured on freshly prepared MRS agar plates. All experiments and cultures were done in completely sterile conditions to avoid any fungal contaminations.
Morphological, physiological and biochemical characterization of LAB isolates
Preliminary identification of the bacterial isolates was carried out by colony morphology, cultural characteristics, and microscopic observations. The isolates that were identified as Gram-positive, non-spore forming, and catalase-negative were selected and screened by physiological and biochemical tests, which include; catalase test, oxidase test, indole test, methyl red test, Voges Proskauer (VP) test, citrate utilization, salt tolerance, triple sugar iron test (TSI), arginine dehydrolase, and sugar fermentation test using three different sugars (glucose,…
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