1. Membrane filters: These filters are made from a variety of polymeric materials such as cellulose nitrate, cellulose diacetate, polycarbonate and polyester. The older type of membrane, called gradocol (graded colloidion) membrane was composed of cellulose nitrate. Gradocol membranes have average pore diameter of 3-10 µm. The newer ones are composed of cellulose diacetate. These membranes have a pore diameter ranging from 0.015 µm to 12 µm. These filters are sterilized by autoclaving. Membrane filters are made in two ways, the capillary pore membranes have pores produced by radiation while the labyrinthine pore membranes are produced by forced evaporation of solvents from cellulose esters. The disadvantages of depth filters are migration of filter material into the filtrate, absorption or retention of certain volume of liquid by the filters, pore sizes are not definite and viruses and mycoplasma could pass through. The advantages of membrane filters are known porosity, no retention of fluids, reusable after autoclaving and compatible with many chemicals. However, membrane filters have little loading capacity and are fragile. Air Filters: Air can be filtered using HEPA (High Efficiency Particle Air) filters. They are usually used in biological safety cabinets. HEPA filters are at least 99.97% efficient for removing particles >0.3 µm in diameter. Examples of areas where HEPA filters are used include rooms housing severely neutropenic patients and those operating rooms designated for orthopedic implant procedures. HEPA filter efficiency is monitored with the dioctylphthalate (DOP) particle test using particles that are 0.3 µm in diameter. SONIC AND ULTRASONIC VIBRATIONS: Sound waves of frequency >20,000 cycle/second kills bacteria and some viruses on exposing for one hour. Microwaves are not particularly antimicrobial in themselves, rather the killing effect of microwaves are largely due to the heat that they generate. High frequency sound waves disrupt cells. They are used to clean and disinfect instruments as well as to reduce microbial load. This method is not reliable since many viruses and phages are not affected by these waves. CHEMICAL METHODS OF DISINFECTION: Disinfectants are those chemicals that destroy pathogenic bacteria from inanimate surfaces. Some chemical have very narrow spectrum of activity and some have very wide. Those chemicals that can sterilize are called chemisterilants. Those chemicals that can be safely applied over skin and mucus membranes are called antiseptics. An ideal antiseptic or disinfectant should have following properties: ƒ Should have wide spectrum of activity ƒ Should be able to destroy microbes within practical period of time ƒ Should be active in the presence of organic matter ƒ Should make effective contact and be wettable ƒ Should be active in any pH ƒ Should be stable ƒ Should have long shelf life ƒ Should be speedy ƒ Should have high penetrating power ƒ Should be non-toxic, non-allergenic, non-irritative or non-corrosive ƒ Should not have bad odour ƒ Should not leave non-volatile residue or stain ƒ Efficacy should not be lost on reasonable dilution ƒ Should not be expensive and must be available easily Such an ideal disinfectant is not yet available. The level of disinfection achieved depends on contact time, temperature, type and concentration of the active ingredient, the presence of organic matter, the type and quantum of microbial load. The chemical disinfectants at working concentrations rapidly lose their strength on standing. Classification of disinfectants: 1. Based on consistency a. Liquid (E.g., Alcohols, Phenols) b. Gaseous (Formaldehyde vapor, Ethylene oxide) 2. Based on spectrum of activity a. High level b. Intermediate level c. Low level 3. Based on mechanism of action a. Action on membrane (E.g., Alcohol, detergent) b. Denaturation of cellular proteins (E.g., Alcohol, Phenol) Autoclave Indicator TapeBowie & Dick Test PacksIndicator LabelsMulti-Variable Steam IndicatorClass 4Steam IndicatorClass 6Helix Control Test PackageContainer SealsContainer Keysterilization equipmentssterilization productssterilization controlsterilization monitoringbowie dick test, infection controlcssdSteam sterilization

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