Thesis
Improvement of detection method and heat resistance study among strains of Enterobacter sakazakii
Washington State University
Master of Science (MS), Washington State University
2007
Handle:
https://hdl.handle.net/2376/102892
Abstract
Enterobacter sakazakii is a rare, but important cause of life-threatening neonatal meningitis and has also been associated with bacteremia and necrotizing enterocolitis. Although the natural habitat and reservoir of this pathogen remain unknown, several outbreaks had been associated with infant formula. This study was carried out to evaluate recommended enrichment broths, develop an effective quantitative analysis method, compare heat resistance among strains, and provide a guideline for infant formula preparation and handling. First, reconstituted dried infant formula (DIF), Enterobacteriaceae enrichment (EE) broth, modified tryptone soya broth supplemented with novobiocin, modified Escherichia coli broth with novobiocin, and buffered peptone water supplemented with vancomycin, cefixime, and cefsulodin were compared for enriching E. sakazakii. EE broth was the most effective of five enrichment broths, followed by reconstituted DIF. Second, a new method was developed to effectively enumerate E. sakazakii by fluorescence. Ninety six-well microtiter plates were used to perform a miniaturized 10-tube MPN enumeration protocol. This procedure was highly correlated (R 2 = 0.91) with the traditional plating method in reconstituted DIF and required much shorter time (<10 h) and less media. Other than improving the detection method, heat resistance of E. sakazakii among four strains was compared in pH 7.0 phosphate buffer (PB) and reconstituted DIF. No significant (p<0.05) difference was observed at 50°C. However, as treatment temperature increased, the differences among four strains became distinguishable. The four strains were separated into two groups when 60°C was applied. Compared to PB, reconstituted DIF could protect cells from being heat damaged. At the last part, either one serving or two servings of infant formula were reconstituted by mixing with different temperatures of water including room temperature (24±1°C), 50°C, 70°C, 80°C, and 90°C. According to the survival and regrowth curves, it is proved that when hot water (70-90°C) was used, at least 1 log reduction was achieved. Therefore, E. sakazakii infection could be reduced by reconstituting DIF with hot water.
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Details
- Title
- Improvement of detection method and heat resistance study among strains of Enterobacter sakazakii
- Creators
- Pei-Chun Chen
- Contributors
- Dong-Hyun Kang (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Food Science, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525165801842
- Language
- English
- Resource Type
- Thesis