Phenol was introduced into surgical practice by
Answer: A
Lister used carbolic acid on wounds, dressings and in the operating theatre, and the fall in post-operative sepsis established antiseptic surgery. Pasteur and Koch shaped the germ theory it rested on, and Fleming's work on penicillin came much later.
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Phenolic disinfectants act by
Answer: B
At working strengths phenolics disrupt the cell membrane and precipitate cell proteins. They keep much of their activity in the presence of organic matter, which is why they remain useful on floors and in laboratory discard jars.
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Iodophors are preparations in which iodine is
Answer: C
Combining iodine with a carrier such as povidone reduces staining and irritation while releasing free iodine steadily, which is why iodophors replaced tincture of iodine for skin preparation. The active agent is still the free iodine.
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Chlorine and hypochlorite act as disinfectants because they are
Answer: D
Hypochlorous acid oxidises sulphydryl groups and other cell constituents, giving rapid broad-spectrum killing including spores at high strength. Activity falls sharply in the presence of organic matter, so surfaces are cleaned before they are disinfected.
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The oligodynamic action of heavy metals refers to their
Answer: A
Correct answer: antimicrobial effect at very low concentrations
Oligodynamic action is the inhibition of microorganisms by metal ions at concentrations far below those needed for any chemical bulk effect - silver being the classic example, and the reason silver-impregnated dressings and catheters are used. The ions bind to sulphydryl groups in microbial enzymes, denaturing them at trace concentrations.
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Quaternary ammonium compounds are
Answer: B
Being positively charged surfactants they adsorb to the negatively charged cell surface and disorganise the membrane. They are low-level disinfectants: pleasant to use and non-corrosive, but inactive against spores and unreliable against mycobacteria.
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Quaternary ammonium compounds are antagonised by
Answer: C
Anionic soap carries the opposite charge and neutralises a cationic surfactant, so residual soap on a surface destroys the disinfectant's activity. Rinsing between cleaning and disinfection is therefore essential when these agents are used.
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Glutaraldehyde and formaldehyde kill microorganisms by
Answer: D
Aldehydes add alkyl groups to amino and other reactive groups, cross-linking proteins and nucleic acids. Because that action extends to spores, a two per cent glutaraldehyde solution counts as a high-level disinfectant and, with long enough contact, a chemical sterilant.
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Glutaraldehyde is usually employed at a concentration of about
Answer: A
Two per cent alkaline glutaraldehyde is the standard preparation for heat-sensitive instruments such as endoscopes. It is sporicidal on prolonged contact, and its irritant vapour is the reason it must be used in a ventilated area and rinsed off thoroughly.
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Ethylene oxide is valuable as a sterilant because it
Answer: B
As a gas it penetrates packaging and complex devices and works near ambient temperature, so plastics and electronics survive. The drawbacks are a cycle measured in hours, flammability, and toxic residues that demand a long aeration period afterwards.
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