Why we don't get sick: The within-host population dynamics of bacterial infections

To pathogenic microparasites (viruses, bacteria, protozoa, or fungi), we an d other mammals (Living organisms at large) are Little more than soft, thin -walled flasks of culture media. Almost every time we eat, brush our teeth, scrape our skin, have sex, get bitten by insects, and inhale, we are confr onted with populations of microbes that are capable of colonizing the mucos a lining our orifices and alimentary tract and proliferating in fluids and cells within us. Nevertheless, we rarely get sick, much Less succumb to the se infections. The massive numbers of bacteria and other micro- and not-mo- micro organisms that abound and replicate in our alimentary tract and cover our skin and the mucosa Lining our orifices normally maintain their commun ities in seemingly peaceful coexistence with the somatic cells that define us. Why don't these microbes invade and proliferate in the culture media wi thin the soft, thin-walled flask that envelops us? Why don't they cause dis ease and Lead to our rapid demise?