Some bacteria can potentially cause us to be ill. These are known as pathogenic bacteria, or pathogens. The time between the entry of the bacteria into our bodies and the disease they cause can vary. Some bacteria cause illness quickly, others can live inside us for years, not causing illness until the conditions are favourable. Bacteria make us ill in two ways:
We also feel ill because of our body's response to infection. See the Immune System section for more details. Some bacteria can form spores. These are tough coatings to protect the bacterial cell from harsh environmental conditions. By forming spores bacteria can stay dormant in unfavourable conditions until they improve, at which point they can begin to function normally again. See 'Notes on Medical Microbiology' for more information.
- by spreading throughout our body (called invasiveness)
- by producing poisonous substances called toxins when inside our body.