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Lactobacilli play an important role in food, industrial and clinical applications. Lactobacillus has been associated with therapeutic effects in humans and animals, mainly induction of immunity, competition with pathogens and reduction of blood cholesterol. In this study, lactic acid bacteria (LAB) were isolated from different food and non–food samples according to morphological and physiological characteristics and tested for stress tolerance, blood hemolysis, histamine formation, antimicrobial, antioxidant and antitumor activity and cholesterol reduction ability.Most of the isolates were tolerant to acidic and alkaline conditions (pH 2.5, 3.5 and 9) for 3 and 6h, osmotic stress (3 M NaCl) and heat stress (55 and 70oC). However, all bacterial isolates were more susceptible to oxidative and bile stress. All the isolates didn’t show any hemolytic activity or histamine formation. The isolates also exhibited anti–bacterial, anti–yeast and antioxidant activities.
All the isolates exhibited cholesterol reduction with varying potencies, depending on the time of incubation, ranging from 23 to 82% after 48h and from 53 to 91% after 120h. Most of the isolates also were able to deconjugate bile salt mixture and exhibited bile salt hydrolase (BSH) activity which ranged from 22 to 44% after sonication and from 23 to 54% after treatment with cetyl trimethyl ammonium bromide (citrimonium bromide (CTAB)); moreover the use of active cells showed much better BSH activity (ranged from 36 to 142.9 U/mg cells). Eight out of the thirty-five tested isolates were the most tolerant organisms that exhibited cholesterol reduction in vitro which ranged from 48˗82% and 72˗91% after 48 and 120h, respectively. They also expressed higher amount of BSH ranging from 90 to 142 U/mg using active cells. The nucleotide sequence of 16S rRNA of the eight isolates revealed that they’re belonging to two species of lactobacilli; Lactobacillus plantarum and Lactobacillus rhamnosus.
The efficiency of two identified cholesterol–lowering isolates with probiotic traits on promoting lipid profile was evaluated in Westar rats fed with cholesterol–rich diet. The effect of Arabic gum as a prebiotic was also tested. The results indicated that blood cholesterol and triglyceride levels of probiotic–administered rats were reduced to a great extentcompared to those prebiotic or synbiotic controls. The results suggested that the two probiotics L. plantarum KU985433 and L. rhamnosus KU985436 could be used as food ingredients to reduce cholesterol and consequently prevent heart disease, thus avoiding the severe side effects of cholesterol–lowering drugs.
Probiotics, LAB, Lactobacillus, stress tolerance, cholesterol reduction, BSH activity, molecular identification, in vivo application.