Aseptic meningitis is not caused by bacteria.
滅菌 refers to the process of sterilization, whereas 無菌性 describes the resulting sterile state.
aseptic meningitis
Compound of 無 (mu, 'without') + 菌 (kin, 'bacteria/germ') + 性 (sei, 'nature/characteristic'). The exact historical derivation is uncertain, but the components clearly indicate 'the quality of being germ-free'.