<P> Many antiviral drugs are designed to treat infections by retroviruses, mostly HIV . Important antiretroviral drugs include the class of protease inhibitors . Herpes viruses, best known for causing cold sores and genital herpes, are usually treated with the nucleoside analogue acyclovir . Viral hepatitis is caused by five unrelated hepatotropic viruses (A-E) and can be treated with antiviral drugs depending on the type of infection . influenza A and B viruses have become resistant to neuraminidase inhibitors such as oseltamivir and the search for new substances is on . </P> <P> Antiparasitics are a class of medications indicated for the treatment of infection by parasites, such as nematodes, cestodes, trematodes, infectious protozoa, and amoebae . Like all antimicrobials against intracellular microbes, they must kill the infecting pest without serious damage to the host . </P> <P> A wide range of chemical and natural compounds are used as antimicrobials . Organic acids are used widely as antimicrobials in food products, e.g. lactic acid, citric acid, acetic acid, and their salts, either as ingredients, or as disinfectants . For example, beef carcasses often are sprayed with acids, and then rinsed or steamed, to reduce the prevalence of E. coli . </P> <P> Copper - alloy surfaces have natural intrinsic antimicrobial properties and can kill microorganisms such as E. coli, MRSA and Staphylococcus . The United States Environmental Protection Agency has approved the registration of 355 such antibacterial copper alloys . As a public hygienic measure in addition to regular cleaning, antimicrobial copper alloys are being installed in some healthcare facilities and in subway transit systems . Other heavy metal cations such as Hg and Pb have antimicrobial activities, but can be toxic . </P>

Discuss the factors to be controlled during measurement of antimicrobial activity of antibiotics