Final Examination for the Degree of MSc Food Science for Krishna Gelda
Date and Time
Food Science building - lecture room 128
DEFENCE ANNOUNCEMENT Final Examination for the Degree of MSc
Dr. Loong-Tak Lim, Chair
Dr. Jeff Farber, Advisor
Dr. Gisele LaPointe, Advisory Committee Member
Dr. Keith Warriner, Department Member
TITLE: CHARACTERIZING THE CULTURABLE BACTERIA ISOLATED FROM IMPORTED, READY-TOEAT (RTE) FOODS FOR THEIR ABILITY TO CONTROL LISTERIA MONOCYTOGENES
ABSTRACT: Listeria monocytogenes, an important foodborne pathogen, remains a significant threat to public health as the invasive form of infection can result in high case-fatality rates. This research thesis investigated the culturable microbiota of select imported, RTE foods to see whether the existing bacterial microflora could inactivate, inhibit the growth and/or cause a reduction in the virulence of L. monocytogenes. Among all the foods tested (dried apple slices, cumin seeds, date fruits, fennel seeds, pistachios, pollen, raisins and seaweed), the date fruit microbiota displayed the most promise for harbouring antagonistic properties against L. monocytogenes.
Of the 191 isolates recovered from five different date fruits, 36 (i.e., 19%) produced zones of inhibition against L. monocytogenes that ranged from 0.3 to 5.8 mm. The inhibitory strains were all identified as Bacillus spp. Among those Bacillus spp. that were tested for their ability to inhibit PrfA, all caused a significant reduction in the activation of the PrfA protein (p-value < 0.05). In addition, the anti-Listeria compound(s) produced by B. altitudinis DS11 were found to be proteinaceous in nature, acid and alkali-tolerant and resistant to temperature treatments up to 100oC. The results obtained in this thesis showed the potential for an unconventional RTE food matrix to harbour anti-Listeria compounds and beneficial Bacillus spp. that could be used to control L. monocytogenes.