Bacterial Defense Mechanisms

Endospores

• An endospore is a dormant, tough, non-reproductive structure produced by certain bacteria from the Firmicute phylum.
• Not a true spore (offspring) - but rather a stripped-down, dormant form of the bacteria
• Endospore-forming bacteria produce some of the most potent toxins known
• Usually occurs in GRAM-POSITIVE bacteria - most types of bacteria cannot change to the endospore form, but the most significant clinically significant examples that can are the Bacillus and Clostridium genera:
• Hospital-borne infections:  Clostridium difficile
• Food contamination:   Bacillus cereus,   Clostridium botulinum
• Wound infestation:  Clostridium perfringens, Clostridium tetani
• Bioterrorism:  Bacillus anthracis

Endospore Formation

• When a bacterium detects environmental conditions are becoming unfavorable it may start the process of endosporulation - which takes about eight hours
• Endospore formation is usually triggered by a lack of nutrients - and endospores can survive without nutrients
•  In endospore formation: The bacterium divides within its cell wall then one side engulfs the other
• The endospore consists of: the bacterium's DNA and part of its cytoplasm, surrounded by a very tough outer coating.

Re-Activation

• Endospores enable bacteria to lie dormant for extended periods, even centuries - revival of spores millions of years old has been claimed
• Upon detecting nutrients, the endospore can convert back to actively growing cells - the most common, initial step in this so-called germination process is the recognition of small molecule germinants by germination receptors in the inner-membrane

Endospores are very resilient

• Endospores are resistant to: ultraviolet radiation, desiccation, high temperature, extreme freezing and chemical disinfectants
• Common anti-bacterial agents (that work by destroying vegetative cell walls) do not affect endospores.

Reference: Wikipedia