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Endospores are a bacteria’s defence mechanism, a tough nut to crack and an increasing problem in hospitals. Is there a way that we can effectively reduce their presence in the environment and gain the upper hand in our fight against infection?
An endospore is a dormant cell formed by bacteria as protection against harsh environments. For example, extreme cold/heat, nutrient depletion, desiccation and UV exposure. They’re also resistant to some of our measures to eradicate them e.g., boiling and disinfectants. Sporulation is the process of endospore formation whichthat occurs in an active metabolising cell when unfavourable conditions are detected. The whole process takes approximately 15 hours, resulting in a dormant endospore . See image below.
Image credit: Laura Hooper
The genus Clostridium is one of the most widely studied endospore producing groups due to their its prevalence in hospital environments, i. In particular Clostridium difficile . This anaerobic bacteria causes antibiotic-associated diarrhoea. Infection occurs when a patient ingests C.difficile endospores. These endospores are hardy and survive the patients stomach acid. Once in the colon, the endospores will germinate into active bacterial cells. Enterotoxins A and B are then produced causing the symptoms; of fever, diarrhoea, and weight loss . C.difficile outbreaks are a major problem in hospitals, especially in elderly patients. This bacteria is such a problem because the endospores can survive on surfaces for 5 months or longer! . But how are they so resilient? The key is in the endospore structure:
Image credit: Laura Hooper
An endospore consist of six layers, these layers are in place to protect the DNA. Each layer has a different make-up resulting in resistance to different factors . The two most important layers are:
This is predominantly made up of Cot A-G proteins and presents the first layer of defence against undesirable environments. It is a hydrophobic layer meaning it’s ‘water hating’. This quality results in an endospore’s resistance to hypochlorites such as bleach. The proteins are also cross-linked forming a mesh-like barrier against large molecules. This includes one of our bodies’ defences, lysozymes. These enzymes are found in tears and saliva and function to prevent infection by damaging bacterial cell walls. C.difficile is resistant to stomach acid and even cooking temperatures, due to its incredibly resistant coat , .
This contains the DNA, ribosomes and enzymes, which are essential for the germination of the endospore into an active cell again. In the core there is a low water content which prevents enzymatic activity, allowing resistance to wet heat, (boiling), due to the low molecular action. But perhaps the most important molecules in endospore resistance are the small acid soluble proteins (SASP). These play an important role in DNA protection by binding directly to it in a tube-like structure. By doing this they physically prevent any damage by chemicals, UV radiation and heat , .
The above features of endospores allow them to survive in this dormant state until conditions are once again favourable and they can germinate. The persistence of endospores in hospitals are is a massive issue, as they are hard to remove from the environment e.g., curtains, surfaces and bedding. It is also a challenge to eradicate them from thepatients/doctors hands and bodies of patients and doctors. Aas alcohol sanitising gels, although good for bacterial cells, aren’t effective against C.difficile endospores. The extreme temperatures and harsh detergents that would be needed to penetrate the coat couldn’t be used on skin .
Spores will always be a problem in healthcare environments causing persistent and ongoing outbreaks of disease. So how can we crack this seemingly impenetrable problem? Well the answer seems to lie in causing them to lay down their arms. i.e. germinate! One study suggests that by forcing spores to germinate using a germination solution, i.e.g. minerals, on hospital surfaces you can destroy them more easily. As they become are more vulnerable active cells again, they are more vulnerable usingto cleaning methods such as heat/ UV radiation . Although this study has shown promising results, specifically increased eradication of C.difficile spores, more research is needed on the topic before we can be confident in our battle against endospores.