The human body has about 10 bacterial cells for every eukaryotic cell. bacteria coat our skin, gut, and mouth. also present are protists, archaeans, and viruses. collectively, these organisms are our microbiota. the bacterial species staphylococus aureus is found on the skin and in the nasal passages of about 20% of the human population. in healthy individuals, s. aureus is benign (does not cause harm) in these locations. however, if it is introduced into the bloodstream through, for example, a wound, it can make a person gravely ill. thus, the ecological relationship of s. aureus with a human:
is always mutualistic.
is always antagonistic.
can be mutualistic or antagonistic.
is fixed or unchanging.
is benign.