Type / Description / Examples / Some Disorders That Can Result
Bacteria / Bacteria are microscopic, single-celled organisms / Streptococcus pyogenes / Strep throat
Escherichia coli / Urinary tract infections
Viruses / Viruses are small infectious organisms—much smaller than a fungus or bacterium. They cannot reproduce on their own. They must invade a living cell and use that cell's machinery to reproduce. / Varicella zoster / Chickenpox and shingles
Rhinovirus / The common cold
Fungi / Fungi are neither plants nor animals. Their size ranges from microscopic to easily seen with the naked eye. They include yeasts, molds, and mushrooms. / Candida albicans / Vaginal yeast infections
Tinea pedis / Athlete's foot
Parasites / Parasites are organisms that survive by living inside another, usually much larger organism (the host). They include worms and single-celled animals (protozoa). / Enterobius vermicularis (a pinworm) / Itching around the anus
Plasmodium falciparum / Malaria
http://www.merck.com/mmhe/print/sec17/ch188/ch188a.html