Moist heat sterilisation by autoclaving is superior to dry heat for sterilising culture media containing dextrose because:

• A Dry heat causes caramelisation of dextrose at 160°C, destroying the sugar; autoclaving at 121°C preserves carbohydrates ✓
• B Dry heat kills only vegetative cells while autoclave kills spores at lower temperature
• C Dry heat cannot generate temperatures above 100°C whereas autoclave achieves 121°C under pressure
• D Moisture enhances spore killing by hydrolysing structural proteins of bacterial endospores, while dry heat denatures proteins without hydrolysis

Explanation

Dextrose-containing media (e.g., glucose broth, Robertson's cooked meat broth) cannot be autoclaved at standard 121°C for 15 minutes along with other media components like peptone because the combination of glucose + amino acids causes Maillard (browning) reactions that alter media properties. Instead, dextrose is autoclaved separately at lower temperatures or prepared as filtered sterile solution added aseptically. For the general principle: dry heat at 160°C/1 hour or 180°C/30 minutes is used for glassware, oils, powders — materials damaged by moisture. Moist heat (autoclave) is preferred for media because it works at lower temperatures, and moisture is essential for protein denaturation (coagulation) of bacterial proteins. The statement in option A captures the key practical point that dry heat (160°C+) would caramelise/char dextrose.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.