No abstract available. / Dissertation (MEng)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

Listeria monocytogenes is food-borne pathogen that causes listeriosis in individuals with a compromised immune system and pregnant women. This pathogen can survive in anaerobic conditions present in specially packaged foods as well as the gastrointestinal tract. The purpose of this study is to evaluate virulence of L. monocytogenes F2365 in anaerobic conditions. Another goal of this study is to establish gerbils as the ideal animal model since descrepancies exist in current models. Gerbils were orally infected with one of four doses: 1) phosphate buffered saline, 2) 5X106CFU aerobic dose, 3) 5X108CFU aerobic dose, and 4) 5X106CFU anaerobic dose. Results indicate anaerobically cultured F2365 colonized the intestines consistently throughout the study unlike aerobic cultures. Additionally, intestinal damage was observed in challenged gerbils. Further goals include evaluating how viurlence is influenced in anaerobic conditions with varying bile concentrations and pH levels.

A bifidobacteria mix (nine strains) was evaluated for its effect on the growth and survival of Escherichia coli O157:H7 (ATCC 43890) in 11% NFDM and MRS broth under the optimum growth conditions for E. coli O157:H7 growth (37¡ãC, aerobic). Preliminary experiments were conducted to obtain the growth curves of the 9 strains of bifidobacteria and E. coli O157:H7 and confirm the inhibitory effect of acidity on E. coli O157:H7 (pH of media adjusted to 3.8). Acidapted E. coli O157:H7 showed no difference in resistance toward bifidobacteria (P>0.05) when compared to the non-acid adapted one. Escherichia coli O157:H7 did not survive in the supernatant of the bifodbacteria mix collected after incubation (37¡ãC) with aerobic shaking (8 h). However, the pathogen was able to grow after the pH of the supernatant was adjusted to 6.50 (pH of fresh MRS broth). Results suggest that a high content of bifidobacteria has a strong inhibitory effect on E. coli O157:H7, in part due to the low pH. However, products from bifidobacteria may also exert inhibitory effects.