Ionizing radiation – primary antimicrobial action: Which statement best describes how ionizing radiation (e.g., gamma rays, high-energy electrons) damages microbes?

Introduction:
Ionizing radiation is used for sterilizing heat-sensitive medical products and foods. Its antimicrobial effect stems from ionization events that damage cellular macromolecules.

Given Data / Assumptions:

• Radiation type: gamma rays, X-rays, electron beams.
• Medium contains water, a source of reactive species upon irradiation.
• Target organisms include bacteria, spores, and viruses (dose-dependent).

Concept / Approach:
Ionizing radiation ejects electrons from atoms/molecules, forming ions and reactive radicals (e.g., hydroxyl radicals) that break phosphodiester bonds and modify bases. Direct hits and indirect radical damage together produce lethal DNA lesions that microbes cannot repair at sterilizing doses.

Step-by-Step Solution:
Identify the physical event: ionization → electron ejection. Trace consequences: radical formation in water → macromolecular damage. Connect to outcome: loss of viability due to DNA/protein injury. Choose the option that explicitly mentions ionization and radicals.

Verification / Alternative check:
Dosimetry curves correlate sterilization assurance levels with absorbed dose (kGy), consistent with cumulative ionization damage rather than simple heating.

Why Other Options Are Wrong:
Protein “2-D” conversion or mere enzyme slowing misrepresent mechanisms.

Heating-only models apply to microwave/infrared, not to ionizing radiation chemistry.

“None” is false because the mechanism is well established.

Common Pitfalls:
Assuming radiation acts like dry heat; ionization chemistry is the critical difference.

Final Answer:
Ejects electrons from molecules (ionization), generating radicals that attack DNA and vital targets.