SCREENING OF POTENTIAL PROBIOTIC LACTIC ACID BACTERIA FROM DIFFERENT SOURCES BY In vitro TESTS

Abstract

A total of 87 isolates of lactic acid bacteria (LAB) were isolated anaerobically from different food sources (yoghurt; Domiati cheese; fresh and fermented milk; mixed pickles and green olives), as well as human breast milk and infant stools. Only ten isolates showed high tolerance to pH 3.0 for three hours and therefore they were chosen for other studies. The selected isolates were identified based on physiological, biochemical and MALDI-TOF mass spectrometry identification. The most frequently observed genus was Lactobacillus (8 isolates) and one isolate seemed to be Enterococcus faecium and another isolate showed that it is Bifidobacterium bifidium. All of the tested species with a score value between 2.000 to 2.484 (100%) were correctly identified by MALDI-TOF-MS to the genus and species levels. The majority of LAB species were tolerant to 0.3% bile salts for up to 4 hrs but L. fermentum was the most tolerant. Four species exhibited partial bile salt hydrolase activity. All of the species survived in 1 mg/ml pancreatin for 4 hrs. However, two of them showed 1/10 decrease in their numbers. Eight species were non haemolytic. Most of the tested species were resistant to penicillin (10 µg), ciprofloxacin (5 µg), gentamycin (10 µg) and streptomycin (10µg). However other species showed variable resistance against the ten tested antibiotics according to NCCLS. The cell free supernatant of L. acidophilus (IS9) showed the highest antimicrobial property against all the indicator pathogens tested specially Staphylococcus aureus and Klebsiella pneumoniae. Therefore, these 10 species were found, in vitro, to possess desirable properties in order to use as probiotic for human consumption.