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: 56 oC– 25 % water: 74-80 oC– 18 % water: 80-90 oC– 6 % water: 145 oC– 0 % water: 160-170 oC

• Time-temperature in sterilization with dry air (to inactivate bacterial spores)– 170 oC for 60 min– 160 oC for 120 min– 150 oC for 150 min– 140 oC for 180 min– 121 oC 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, powers, sharp instruments, and glassware

Moist heat (I)

• Mechanism: protein denaturation, enzyme inhibition, RNA and DNA breakdown

• Advantage– Low temperature and short sterilization period

(121 oC for 15-30 min)

• Disadvantage– Less penetration– Moisture damage

Moist heat (II) (A steam autoclave)

Ionizing radiation (I)

• Electromagnetic radiations: γ radiation, x-ray, 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