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.

can be mutualistic or antagonistic.

Explanation:

According to the given information, the bacterial species Staphylococcus aureus present in some nasal passages and on the skin do not harm the person. The ecological interaction wherein both organisms are benefited and none is harmed is known as mutualism. Here, Staphylococcus aureus does not cause any disease in human when present on the skin and in the nasal passage, that is both are in mutualism.

However, when present in the bloodstream, the same bacterial species can cause infections such as sepsis and represents antagonist effects on the host.  

Hence, the staphylococcus aureus species may be mutualistic or antagonistic to human.  

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