Medical microbiology may overlap with parasitology, generally considered the study of diseases caused by multi-cellular parasites, where a parasite is defined as an organism that derives its nutrients from another living organisms, often but not always to the detriments of its host. Microbes are continually probing our defences and commensals that get into the wrong place can do untold damage. A very small minority of microbes are primary pathogens. These are ...
