Q.72 Which of the following is NOT an accepted method for sterilization?
(A) Autoclaving (B) X–rays
(C) Gamma rays (D) UV rays

UV Rays is not an accepted method for sterilization among the options. Autoclaving uses moist heat under pressure to achieve complete sterility, while ionizing radiations like X-rays and gamma rays penetrate materials to destroy microbial DNA effectively. UV rays, however, only disinfect surfaces due to poor penetration and inability to kill all spores reliably.

Option Analysis

• (A) Autoclaving: This gold-standard method employs steam at 121°C and 15 psi for 15-20 minutes, hydrolyzing proteins and killing all microbes including spores through deep penetration.

• (B) X-rays: An emerging ionizing radiation technique per ISO 11137 standards, X-rays generated from electron accelerators damage microbial DNA with excellent penetration for medical devices.

• (C) Gamma rays: Widely used ionizing radiation from Cobalt-60 sources, it penetrates packaging to inactivate microbes by DNA disruption without residues or heat, achieving SAL 10^{-6}.

• (D) UV rays: Non-penetrating UV-C light (254 nm) forms DNA dimers on exposed surfaces only, failing to sterilize opaque or complex items and ineffective against spores in shadows.

Sterilization methods are crucial in microbiology and biotechnology for ensuring asepsis, especially for CSIR NET life sciences exams. Not an accepted method for sterilization among common options is UV rays, due to its surface-level disinfection limits. This article breaks down autoclaving, X-rays, gamma rays, and UV rays to clarify why.

Autoclaving: Moist Heat Standard

Autoclaving remains the most reliable physical sterilization method using pressurized steam at 121°C for 15-20 minutes, achieving complete microbial kill via protein coagulation and spore destruction. It penetrates dense materials effectively without chemicals.

X-Rays and Gamma Rays: Ionizing Radiation Powerhouses

Both X-rays and gamma rays qualify as accepted sterilization methods under ISO 11137, breaking DNA bonds for deep penetration in packaged medical devices. Gamma from Co-60 offers high throughput; X-rays provide faster, on-demand dosing.

UV Rays: Why Not Sterilization?

UV rays fail as a true sterilization method because they cannot penetrate solids, dust, or shadows, merely disinfecting surfaces by forming thymine dimers in exposed DNA. Guidelines like CDC limit it to safety cabinets, not full sterility assurance.