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Chapter 1 : Bacillus cereus and Other Bacillus spp.
Category: Food Microbiology; Applied and Industrial Microbiology
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Bacillus spp. are gram-positive, endospore-forming facultatively anaerobic bacteria. The resistance of their spores to adverse conditions has resulted in widespread distribution of the organism. The bacteria of the genus Bacillus are usually free living, that is, not host adapted, and their spores are widely distributed throughout nature. The spores of Bacillus cereus are ellipsoidal and central to subterminal and do not distend the sporangia. Early in the growth cycle vegetative cells are gram positive, but cells may become gram variable when in late log or stationary phase. Colonies on agar media have a dull or frosted appearance. Two distinct types of illness have been attributed to the consumption of foods contaminated with B. cereus: the diarrheal syndrome and the emetic syndrome. As well as causing enteric illness, B. cereus has been responsible for postoperative infections, especially in immunocompromised patients. Early experiments relying on monkey feeding trials identified the cause of the emetic syndrome as a toxin because cell-free supernatants produced the same symptoms as cell cultures. Germination of spores requires the presence of purine ribosides and glycine or a neutral l-amino acid. Fourier transform infrared spectroscopy can provide a way to differentiate bacterial genera and species through unique Fourier transform infrared vibrational combination bands produced from active components of bacterial cells. Control against food poisoning should be directed at preventing germination of spores and minimizing growth of vegetative cells.
Key Concept Ranking
- Fourier Transform Infrared Spectroscopy