Right choice is (a) Staphylococcus aureus
Best explanation: Staphylococcus aureus is not found in human excreta. It is a round-shaped bacterium that is a member of the Firmicutes. It is mainly found on the upper respiratory tract and/or on skin. But they can also spread through the bloodstream and infect distant organs. Infections caused due to this bacterium can be transferred through the air, skin contact, etc.