Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/33302
Title: Formation of Salmonella Typhimurium Biofilm Under Various Growth Conditions and its Sensitivity to Industrial Sanitizers
Authors: NGUYEN NGOC HAI DUONG
Keywords: biofilm, Salmonella Typhimurium, sanitizers, growth condition, biofilm formation
Issue Date: 16-Jan-2012
Source: NGUYEN NGOC HAI DUONG (2012-01-16). Formation of Salmonella Typhimurium Biofilm Under Various Growth Conditions and its Sensitivity to Industrial Sanitizers. ScholarBank@NUS Repository.
Abstract: Biofilm is defined as a biologically active matrix of cells and extracellular substances in association with a solid surface (Bakke, Trulear, Robinson, and Characklis, 1984). The biofilm can grow as thick as a few micro millimeters within a few days depending on the culture conditions and the species. Understanding the effect of temperature and pH on biofilm formation is essential to prevent their formation, and can reduce the risk of ineffective sanitation and microbial contamination. The effect of food-related stress factors, namely temperature and pH, on biofilm formation and resistance of Salmonella Typhimurium, one of the most important foodborne pathogens, to industrial sanitizers was evaluated in this study. This thesis consists of two experimental studies. In the first study, the effect of different temperatures (28, 37 and 42 ?C) and pHs (6 and 7) on biofilm formation capability of S. Typhimurium on stainless steel and acrylic was investigated. The rate of biofilm formation increased with increasing temperature and pH, while the number of attached cells after 240 h decreased with increasing temperature and was not different between pH 6 and 7. The surface hydrophobicity of bacterial cells was not significantly (p > 0.05) different among the tested conditions. Electron-donating/accepting properties were changed by pH and temperature, although such changes did not correlate with biofilm formation ability under respective conditions. Attachment of S. Typhimurium showed a preference to stainless steel than acrylic surface under all conditions tested, implying that acrylic was less adherent than stainless steel. This result suggests that acrylic should be considered in the food industry where possible. Moreover, this study indicates that hurdle technology using lower temperatures and pHs would help to delay biofilm formation on food contact surfaces when the product is contaminated with S. Typhimurium. In the second study, the aim was to understand how the above mentioned factors affected on the resistance of S. Typhimurium biofilm against industrial sanitizers. The sanitizers tested were quaternary ammonium compounds (QAC, 200 ppm), mixed peroxyacetic acid/organic acids (PAO, 0.1%) and sodium hypochlorite (chlorine, 50 ppm). It was observed that, for biofilms formed at pH 7-37 ?C, chlorine was the most effective sanitizer, followed by QAC and PAO. For all conditions tested, attachment surfaces didn?t cause any significant difference in biofilm resistance against sanitizers. Increasing in biofilm age led to an increase in resistance to sanitizers, although such effect varied by growth condition and sanitizer. The resistance of biofilm formed on stainless steel at pH 6-37 ?C increased with increasing biofilm ages. The effect of temperature and pH on biofilm resistance was dependent on biofilm ages. For 168-h biofilm formed at pH 6, the resistance to all three sanitizers was highest for 37 ?C, followed by 28 and 42 ?C; while for biofilm formed at 37 ?C for 168 h, pH 6 condition increased biofilm resistance to QAC and PAO, but not chlorine, compared with pH 7. These results indicate that the resistance of biofilms against sanitizers was dependent on multiple factors, including biofilm age, temperature, and pH. In summary, this thesis contributes to knowledge in relation to understanding the formation of biofilm and its resistance against industrial sanitizers under food-related stressed conditions. Although the mechanism remained unknown and further research is required, the present results demonstrated that acidic condition such as pH 6 or growth temperature of 37 ?C may induce the formation of resistant biofilm in food industry, posing an additional risk of cross-contamination. In addition, this thesis could assist in the development of more effective sanitizing strategy to ensure complete removal of such resistant biofilm.
URI: http://scholarbank.nus.edu.sg/handle/10635/33302
Appears in Collections:Master's Theses (Open)

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