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the holder method (low temperature long time, LTLT, heated at 63°C for 30 min) and flash method (high temperature short time, HTST, heated at 72°C for 15 sec) followed by quick cooling. Other pasteurisation methods are also available, such as Ultra-High Temperature (UHT) at 140–150°C for 1–3 seconds. (d) Heating and flaming: Many objects are sterilised in the absence of water by dry heat sterilisation. The articles, such as inoculation loops, straight wires, tips of forceps and searing spatulas are sterilised by holding them in Bunsen flame till they become red hot. While, some articles, such as mouth of test tubes, flasks, glass slides, etc., are passed through the flame for a few times without allowing it to become red hot. Hot air oven is also used to sterilise glassware. Sterilisation by Radiation Two types of radiations, namely, ionizing and non-ionizing radiations are used for sterilisation. As radiation does not generate heat, so sterilisation by radiation is termed as ‘cold sterilisation’. Non-ionizing radiations, such as UV rays have the germicidal activity in the wavelength range of 200–280 nm, with 260 nm being the most effective. UV rays induce the formation of thymine—thymine dimers, which ultimately inhibits DNA replication and induces mutation in cells. UV radiation is useful for surface disinfection, i.e., to disinfect culture lab, laminar hood, operation theatres, virus laboratories and etc. The disadvantages of UV rays include their harmful effect on skin and eyes, and reversal action of damage due to DNA repair bacterial enzymes. Ionizing radiations are of two types, particulate (electron beams) and electromagnetic rays (gamma rays). Electron beams are used to sterilise syringes, gloves, dressing packs, foods and pharmaceuticals, etc. Electromagnetic rays have more penetrative power than electron beam, but require longer time of exposure. These radiations damage the nucleic acid of the microorganism. Electromagnetic radiations are used to sterilise disposable Petri dishes, plasticsyringes,antibiotics,vitamins,hormones,glassware and fabrics. 155 Microbial culture Reprint 2025-26