Thesis (M.Sc.) - Cairo University - Faculty of Pharmacy - Department of Microbiology and Immunology

A total of 51 lactic acid bacteria (LAB) were isolated and characterized from 75 different raw food samples among which Lactobacilli represented 70% of the total isolates, followed by Lactococci 12 %, Pediococci 9 %, Leuconostocs 7 % and Streptococci 2 %. Evaluation of the probiotic and prebiotic activities were done to all isolates. Ten isolates were chosen to be acid/bile tolerant, biofilm forming, broad spectrum antimicrobial, and producing Ý-galactosidase, they also could assimilate more than 50 % of cholesterol and produce exopolysaccharides. The selected isolates were further identified by 16S rRNA gene sequencing as strains of Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus reuteri, Enterococcus faecalis, Enterococcus faecium, Pediococcus acidilactici. Screening for the sucrose metabolizing enzymes through reducing sugars production among the 10 isolates was done. Results revealed that isolates I40l Lactobacillus reuteri gave 468.5 og/ml and C7 Lactobacillus fermentum gave 57.9 og/ml reducing sugars. Comparative genomics between the 2 isolates showed that I40l Lactobacillus reuteri had sucrose phosphorylase enzyme (scrp) and levansucrase enzyme (ftfA) while C7 Lactobacillus fermentum had invertase enzyme (bfrA) which was confirmed by PCR on their specific genes (scrp) at 707 bp (ftfA) at 900 bp and (bfrA) at 479 bp respectively. The isolate I40l Lactobacillus reuteri had the ability to metabolize the anti-nutritive sugar raffinose that cause flatulence and abdominal discomfort and produced 371 og/ml reducing sugars.

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