Lecture - Bacterial Spores

Lecture - Bacterial Spores - SPORES AND THEIR SIGNIFICANCE...

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SPORES AND THEIR SIGNIFICANCE Sporulation: spore formation Initiates as response to slowed growth, starvation or pheromones Extensively studied in Bacillus. Refractive (phase bright) with phase-contrast microscopy
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Distribution of Sporeformers All Gram positives: Bacillus cereus, B. anthracis (aerobes ) Clostridium botulinum, C. perfringens (anaerobes ) Found in soils or symbionts of mammals, insects
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C. botulinum: Club shape: spores swell sporangium Principal hazard in canned foods Pre-formed toxin C. perfringens: Normal human intestinal flora Grows rapidly in cooked foods Produces an enterotoxin (C. tetani tennis racket)
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Bacillus cereus Spores in milk, cereals, starches, herbs, spices and other dried foods Pre-formed toxin: emetic or diarrheal disease Low numbers of spores Control directed at preventing germination Cooled to 7° C or heated to above 60° C. Bacillus anthracis Spores in soil, associated with herbivores Enterotoxin toxin extremely lethal
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FOOD INDUSTRY Low acid foods (ph>4.6) problem Spoilage from psychrotrophic Clostridia and fungi Canned , bottled or any sealed container foods Inactivation of C. botulinum spores - Most heat resistant (D 121= 0.21 min) - Elimination (12D) requires 121 C for 3-6 min - At the center of the food - Aseptic processing
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INDUCTION OF SPORULATION Spores increase as growth rate decreases Laboratory mechanism for induction: Limitation of nutrients (carbon or nitrogen). Shifting from rich to poor medium Decoyinine (inhibits guanine nucleotide biosynthesis) Initiation to completion: about 8 hours.
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Catabolite repression - Repressed by limited availability of carbon sources Growth phase dependent Quorum sensing : Modulated by cell-density Small molecules secreted into the medium Peptide pheromones signal cell density: ComX and CSF (competence and sporulation factor) Regulation of Sporulation
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Click to edit Master subtitle style Quorum Sensing Starvation or stationary phase response that alters gene expression to allow extended
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Lecture - Bacterial Spores - SPORES AND THEIR SIGNIFICANCE...

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