The operating room is kept in a sterile condition.
This milk is sold in aseptic packaging.
They sterilize the operating room before starting the surgery.
The culture medium must be kept in a sterile condition.
殺菌 refers to the act of killing germs, whereas 無菌 describes the resulting state of being germ-free.
滅菌 is the stronger medical term for complete sterilization (an action), while 無菌 denotes the germ-free state itself.
Compound of 無 (mu, 'without') and 菌 (kin, 'germ/bacteria'). The reading is on'yomi.