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Individual antimicrobial processes Common sterilizers and disinfectants • Sterilizers – Physical • Dry heat (> 160 oC) • Most heat (>121 oC) • Ionizing radiation – Chemical • Gaseous chemicals • Disinfectants – Physical • Ultraviolet radiation • Hydrostatic pressure – Chemical • • • • • • • Surface-active agents Phenolic compounds Iodine and iodine compounds Peoxygen compounds Chlorine species (free chlorine, chloramines) Chlorine dioxide Ozone Sterilizers Dry heat (I) • Mechanism: protein denaturation, enzyme inhibition, and RNA and DNA breakdown • Protein coagulation (complete denaturation) (e.g. egg albumin) – – – – – 50 % water: 56oC 25 % water: 74-80oC 18 % water: 80-90oC 6 % water: 145oC 0 % water: 160-170oC • Time-temperature in sterilization with dry air (to inactivate bacterial spores) – – – – – 170oC for 60 min 160oC for 120 min 150oC for 150 min 140oC for 180 min 121oC for overnight Dry heat (II) • Advantages – Deep penetration – Less corrosivity • Disadvantages – High temperature – Long sterilization period – Deterioration of materials • Used only for those materials that can not be sterilized by moist heat: petroleum, oil, powders, sharp instruments, and glassware Moist heat (I) • Mechanism: protein denaturation, enzyme inhibition, RNA and DNA breakdown • Advantage – Low temperature and short sterilization period (121oC for 15-30 min) • Disadvantage – Less penetration – Moisture damage Moist heat (II) (A steam autoclave) Ionizing radiation (I) • Electromagnetic radiations: γ radiation, xray, and electrons • Particle radiations: α radiation, β radiation, meson, positron, neutrino • Mechanism: single or double-strand breakage in DNA Ionizing radiation (II) Ionizing radiation (III) Ionizing radiation (IV) Ionizing radiation (V) Ionizing radiation (VI) Gaseous chemical sterilization (I) • Alkylating agents (Alkylation of DNA) – – – – Ethylene oxide Propylene oxide Formaldehyde Beta-propiolactone • Oxidizing agents (Oxidation of proteins and nucleic acids) – – – – Hydrogen peroxide Peracetic acid Chlorine dioxide Ozone Gaseous chemical sterilization (II) Gaseous chemical sterilization (III) (Chemical) disinfectants Surface-active agents • Amphiphilic compounds • Anionic, cationic, nonionic, and amphoterics • Cationic surfactants: Quaternary ammonium compounds – Basic structure: • One nitrogen atom • Four carbon atoms covalently linked to the nitrogen atom • An anion eletrostatically linked to the nitrogen atom – Mechanism: Protein denaturation, enzyme inhibition, and disruption of cytoplasmic membrane Quaternary ammonium compounds (I) Quaternary ammonium compounds (II) Quaternary ammonium compounds (III) Quaternary ammonium compounds (III) • Advantages – – – – Low toxicity Low corrosivity Stable at high temperature and wide pH range Relatively tolerable with organic load • Disadvantage – Not effective against viruses, protozoa, and spores – Less effective at low temperature – Inhibited by most anionics and hard water salts Quaternary ammonium compounds (IV) (applications) • General surface disinfectant • Industrial application (hot water in large commercial laundry) • Swimming pool water??? Drinking water (emergency situation)??? Phenol compounds (I) • Structure • Mechanism – Bacteria: denaturation of proteins, inhibition of enzymes, damages on plasma membrane – Viruses and fungi: Unknown Phenol compounds (II) Phenol compounds (III) Phenol compounds (IV) • Advantages – Effective against viruses, bacteria, and fungi – Stable in concentrate – Tolerable for organic load and hard water • Disadvantages – – – – Not effective against spores High toxicity Not effective at low temperature Incompatible with nonionic and cation surfactants Phenol compounds (IV) • General surface disinfectant • Gemicidal soaps and lotions, antiseptics, preservatives in cosmetics, and mouthwash preparation (Listerine) Iodine and iodine compounds (I) • Chemistry • Antimicrobial agents: I2 (free iodine), HOI (hypoiodous acid), H2OI+ (Iodine cation) • Mechanism: protien denaturation, damages in plasma membrane, and nucleic acid breakdown Iodine and iodine compounds (II) Iodine and iodine compounds (III) • Advantage – Effective against viruses, bacteria, fungi, protozoa and bacterial/fungal spores – Low toxicity – Very stable in concentrate • Disadvantages – – – – Chemical hazard (staining) Less effective at low temperature Relatively corrosive at high temperature Expensive Iodine and iodine compounds (IV) Peroxygen compounds (I) • Hydrogen peroxide, peracetic acids, perfomic acid, and perpropionic acids • Mechanism: hydroxyl radicals: proteins, lipids, and DNA • Very effective on most microbes including spores Peroxygen compounds (II) Peroxygen compounds (III) Peroxygen compounds (IV) Peroxygen compounds (V) Peroxygen compounds (VI) • Advantages – – – – – Strong, fast-acting Effective against most microbes including spores No toxicity No environmental concern Effective over wide pH (up to 7.5) and temperature ranges (40 oF – 150 oF) – Stable in concentrate – Tolerable for organic load • Disadvantages – Limited stability at use solution – Corrosive on soft surfaces (brass, copper, and mild and galvanized steel) Peroxygen compounds (VII) • Excellent surface disinfectants • Industrial water systems (Legionella control) • Wastewater disinfection • Antiseptics • Cold sterilization of phamatheuticals (emulsions, hydrogels, ointments, and powders) To be continued