Thesis (Ph.D.) - Cairo University - Faculty of Agriculture - Department of Microbiology

A total of 209 microbial isolates obtained from honey bee products and the gut of honey bees in different life stages in three feeding seasons (sugar feeding season, citrus feeding season and clover feeding season) in Egypt were assessed for in vitro antagonistic activity against human pathogens. Screening for the isolates that have antagonistic effect was done. 64 isolates have an antagonistic effect against one or more pathogens. The most active isolates were identified based on 16S rRNA and 18S rRNA genesfor bacteria and yeast identification, respectively.Five isolates out of 64 showed a high potential to act as probiotics. They are identified by molecular means as Wickerhamomyces anomalus, Lachancea thermotolerans, Zygosaccharomyces mellis, Bacillus licheniformis and Paenibacillus polymyxa. The antagonistic mechanisms were analyzed using cylinder diffusion assay and transmission electron microscopy. All the five isolates exhibited antimicrobial activities with variable spectrum against 6 human pathogens. They show high tolerance to low pH up to 1.5 and tolerate high bile salt concentration up to 3% after 3 hours of incubation. GC/MS analysis of ethyl acetate extract revealed the presence of Heptadecane, Palmitic acid, Dodemorph, Paradehyde, Octadecnonic and Fenoprofenwhich may inhibit the growth of pathogenic bacteria and Candida albicans. Although it seems unconventional to use yeast strains and non-lactic acid bacteria as probiotics, these five isolates have a high potential to be used as probiotics for animals andhumans

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