Final answer:
Autoclaving cannot be used for heat-labile substances due to the high temperatures involved, potentially damaging such materials. Ethylene oxide and ionizing radiation are suitable methods for sterilizing heat-sensitive items. Filtration removes microbes physically, phenol has been a reference for chemical disinfectant effectiveness, and soil is a source of antimicrobial agents.
Step-by-step explanation:
The method that cannot be used for heat-labile substances is C) Autoclaving. Autoclaving employs high temperature and pressure to sterilize materials, which would damage heat-sensitive items. In contrast, the other methods listed, such as ethylene oxide and ionizing radiation, can be used to sterilize materials that cannot withstand high temperatures. Ethylene oxide is a gas sterilant effective at low temperatures, and ionizing radiation uses high-energy particles or waves to sterilize without heat. Chlorine, glutaraldehyde, and ionizing radiation are all suitable for microbial control on various substances, including those that are heat-sensitive.
Filtration is the microbial control method that does not kill or inhibit microbes but physically removes them from samples. The effectiveness of chemical disinfectants has traditionally been compared to that of phenol. Ionizing radiation, including gamma radiation, is an effective way to sterilize heat-labile and packaged materials, as it can penetrate surfaces which nonionizing radiation cannot.
For microbial control on tissues to prevent infection, an antiseptic is suitable. Soil has yielded compounds with the most antimicrobial activity. Alkylating agents like formaldehyde are strong disinfecting chemicals that act at low temperatures, making them an alternative for heat sterilization.