In males there are small numbers in the Urethra. The female only in the vagina has a large resident microbial community that changes with the menstrual cycle. Lactobacillus acidophillus predominates and other acid tolerant types present in low abundance. As we all know blooms of other organisms can occur but do so usually only in response to a disturbance in the lactobacillus population, which allow the pH to rise and other fungal types to take over. From these experimentally raised animals we know that many of the organisms we talked about above may actually be somewhat beneficial to their hosts.
Many parasites exist without ever causing major damage to their hosts.
A parasite that causes a disease is termed a pathogen. Bacteriocins are plasmid-encoded peptides or proteins that are toxic to bacteria related to the producing organism . For example, E. coli produces bacteriocins called colicins which are toxic to other strains of E. coli and some other enteric bacteria. Skin and mucosal linings 2. Flushing by fluids e.g. in the mouth and urinary tract.