As powerful as your immune system is, you will probably still get sick from time to time. There are a few reasons why this happens. First, there are some microbes that are so strong, your immune system can't overcome them. And second, your immune system may become weakened and not able to fight off invaders. Everything on this fun, graphically-exciting site from Pfizer squirms.
Microbial ecology is a rapidly developing scientific discipline.
He had no formal training in science and from the age of sixteen worked as a draper. This seems a bit of an unlikely background for the person who discovered microbes. What's even more interesting is that Antony van Leeuwenhoek's research followed no particular plan and was carried out, largely, with microscopes constructed by himself. The following links are either new discoveries or sites that didn't make it into my newspaper column because of space constraints. Please let me know if any of these addresses have changed.