Why should you worry about tetanus when you hurt yourself with something rusty?
In: Biology
Rust doesn’t cause Tetanus, the bacteria Clostridium tetani does.
Because C. tetani is a type of anaerobic bacterium, it lives and grows in an environment that lacks oxygen. For example, the surface of a rusty nail is a perfect environment to host endospores in part because atmospheric oxygen reacts with iron to form iron oxide. The rusting process binds the oxygen to iron in such a way as to aid in the creation of an anaerobic environment within the layers of surface rust.
**EDIT: Sorry, I felt I needed to add an edit based on some of the other comments in this ELI5 re rusty nails.**
Clostridium tetani bacteria is ubiquitous outdoors. It is an organism that feeds on dead things; it decomposes plant and animal matter through several fermentative pathways and is part of a massive microbiome that makes up soil. The Clostridia bacteria will grow and multiply in an environment that is low in oxygen, wet, dark, and surrounded by plant or animal matter.
Now take a moment to imagine what a nail is typically pounded into.
Yup, C. tetani eats and grows in decomposing wood. So, imagine that nail hammered into a fence post and left outdoors exposed to the rain. Endospores of C. tetani will be blown around as dust from the soil and act like little seeds that will land in the nooks and crevices around the nail head. The spores will germinate and then work their way into the wet cellulous rich environment surrounding the nail. The iron in the nail will react with atmospheric oxygen to create an anaerobic environment and the bacteria will multiply and then sporulate creating many more spores. The pits and rough scale on the nail can act like a sponge to hold spores of C. tetani. The spores are hearty and are not killed by exposure to the air.
So if you ever do step onto a nail, ask yourself what it may have been hammered into before and if it may actually be a hypodermic petri dish for C. tetani
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