The bacterial spore: nature’s survival package

Introduction Spores of Bacillus and Clostridium species are metabolically dormant and extremely resistant to acute environmental stresses such as heat, desiccation, UV and γ-radiation, mechanical disruption, enzymatic digestion and toxic chemicals. In addition to the spore’s resistance to acute stress, spores can survive for extremely long periods in milder environmental conditions. Indeed, there are several reports suggesting that spores of Bacillus species can survive for millions of years in some special niches1,2. While this latter conclusion remains controversial, there is no doubt that spores of Bacillus and Clostridium species can survive for many, many years3. As a consequence of the persistence of spores and the ubiquity of spore formers in many different environments, spores are common contaminants of foodstuffs and if not dealt with appropriately in food processing may “return to life” via spore germination and outgrowth and then contribute to food spoilage and food poisoning4. In addition to food poisoning (B. cereus, C. perfringens, C. botulinum), there are a number of other human illnesses in which spores play a causative role including, wound infections (gas gangene: C. perfringens; tetanus: C. tetani; wound botulism: C. botulinum; intestinal infection: C. difficile and anthrax: B. anthracis). Spores of B. anthracis persisting in soils are the common route whereby animals acquire pulmonary anthrax. The severity of this disease and the resistance of B. anthracis spores, particularly to desiccation, are undoubtedly major reasons that B. anthracis spores: