Gut, Abraham Majak (2022) Anti-Salmonella Properties of Kefir and Kefir Yeast Isolates: Potential Application in Infection Control and Prevention. PhD thesis, Victoria University.

Abstract

The rise of antibiotic resistance has increased the need for alternative ways of controlling and preventing enteric bacterial infections. Various probiotic bacteria have been used in animals and humans prophylactically and therapeutically. Kefir is an acidic and low alcoholic beverage produced by fermentation of milk, fruit juice, or sugary water with kefir grains and its consumption is associated with prophylactic and therapeutic properties conferred by probiotics components. There is scarce research conducted on kefir and kefir yeast isolates despite claimed potential preventative and curative effect on enteric bacterial pathogens. This thesis investigates traditional kefir and kefir yeast isolates for potential application in the prevention and control of Salmonella in in vitro experiments. Kluyveromyces lactis and Saccharomyces unisporus, Lactobacillus kefiri, and Lactococcus lactis were isolated from kefir and identified using 26s rDNA, ITS region sequencing and MALDI-TOF for yeasts and bacteria respectively. Kefir made from two traditional kefir grains rapidly killed Salmonella Arizoniae and Salmonella Typhimurium possibly due to the action of lactic acid as kefir cell-free supernatant analysis showed high concentration of lactic acid ranging from 83.59 to 229.92 mM. Other compounds with recognized antibacterial activities including carbonyl compounds, histone, cathelicidin, and various peptides were also detected using shotgun proteomics. Kefir yeast isolates showed some potential probiotic properties including survival in the gastrointestinal tract, auto-aggregation, hydrophobicity and lack of hydrolytic enzymes production. These probiotic characteristics were comparable to Saccharomyces boulardii strains used as controls in the study. Adhesion and sedimentation slide agglutination, microscopy, and turbidimetry showed that Salmonella adhered onto yeast cells, which resulted in growth inhibition. Furthermore, yeast-fermented killer toxin medium showed Salmonella growth inhibition likely due to antimicrobial metabolites such as cathelicidin detected by shotgun proteomics in the cell-free supernatant. In conclusion, kefir and kefir yeast isolates may have the potential to control and prevent Salmonella infection.

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