Browsing by Author "Mulaw, Guesh"

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    Microbial Diversity and Probiotic Potential of Lactic Acid Bacteria Isolated from Traditionally Fermented Food Products and Their Applicability for Prevention of Selected Foodborne Pathogens
    (Addis Ababa University, 2019-11-11) Mulaw, Guesh; Tesfaye, Anteneh (PhD); Muleta, Diriba (PhD); Sisay, Tesfaye (PhD)
    Probiotics are live microorganisms which when administered in adequate amounts promote the health of the consumer. The major purpose of this study was to determine bacterial diversity of traditionally fermented food products (teff dough, Ergo and Kocho) and to assess their probiotic potential of lactic acid bacteria in prevention of foodborne pathogens. Culture-independent metagenomic methods, particularly 16S rRNA amplicon sequencing were applied to study the bacterial diversity of some fermented foods. The sequencing of the amplicons resulted in an average of 76,594.33 ± 2,876.25 high-quality reads per sample. The bacterial communities of the three traditional fermented foods were dominated by the phylum Firmicutes, followed by Proteobacteria and Actinobacteria. At the genus level, the prevalent microorganisms were Lactobacillus, Zymomonas, Streptococcus, Leuconostoc, Bacillus and Weissella. The genus Lactobacillus was the most abundant genus in the three studied food products, whereas Zymomonas was the most dominant genus in fermented ergo. In order to assess the probiotic potential of strains isolated from these fermented products, a total of 450 LAB were isolated from the fermented products, and their ability to survive the gastrointestinal conditions was tested. Among them, 34 (7.56%) isolates survived at pH 2 for 3 and 6 h, showing a survival rate of 45.35- 96.33% and 33.33- 91.75%, respectively. All the 34 acid-tolerant isolates survived in the presence of 0.3% bile salts for 24 h with 82.58 to 99.44% rate of survival. The acid and bile salt-tolerant LAB isolates shown inhibiting some bacterial foodborne pathogen into varying degrees. Among the 34 acid and bile salt-tolerant isolates, 9 (26.47%) isolates produced bacteriocins to varying degrees. All ii the 34 acid and bile salt-tolerant isolates displayed sensitivity to ampicillin (10 μg/ml), tetracycline (30 μg/ml) and erythromycin (15 μg/ml), but showed resistance to kanamycin (25 μg/ml), while 17/34 of the isolates were found sensitive/resistant to streptomycin (10 μg/ml). The in vitro adherence to stainless steel plates of the 34 screened probiotic LAB isolates showed adhesion rates that ranged from 29.21 to 41.94%. The identification of 34 screened potential probiotic LAB strains and their genetic relatedness was performed using 16S rRNA gene sequencing and whole-genome (WGS) sequence comparisons. Hence, four isolates were identified as Lactobacillus species including Lb. plantarum, Lb. paracasei subsp. tolerans, Lb. paracasei and Lb. plantarum. The remaining 30 potential probiotic LAB strains were identified by using WGS comparisons. Thus, these isolates belonged to Lactobacillus and Lactococcus species including 22 Lb. plantarum, 1 Lb. paracasei, 1 Lb. brevis and 6 Lc. lactis. Among the 30 potential probiotic LAB strains, BAGEL predicted 1 class III bacteriocin, 7 class II bacterioicins and 3 class I bacteriocins in the genome of 9 strains. The compatibility test among the selected potential probiotic strains (Lb. plantarum, Lb. paracasei and Lc. lactis) showed the absence of antagonism among them. The in vitro antagonism testing of the potential probiotic LAB as separate pure or mixed culture against Salmonella showed a remarkable anti-Salmonella activity with 96.50 to 100% growth inhibition. The combination of strains that showed the highest growth inhibition rates against Salmonella Typhimurium, were used to test their in vivo effect on the colonization of mice by Salmonella Typhimurium. The survival rate of mice on day 21 after the oral challenge with Salmonella Typhimurium was significantly higher (p<0.05) in the experimental pro-typ, treated group (100% survival) when compared with the positive control group (20% iii survival). The counts (colony-forming unit/ml) of Salmonella in feces were significantly lower (p<0.05) for the pro-typ group compared to the positive control group (typ). In general, this study indicates a high level of diversity in the bacterial community structure in traditional fermented foods and the LAB of the traditional fermented food samples was found to be good candidates for food industries as prospective probiotic cultures with health benefits.