Selected important physical and chemical agents are described in the following sections.

Physical Methods

 A. Heat

 Application of heat is the simplest means of sterilizing materials, provided the material is itself resistant to heat damage. A temperature of 100°C will kill all but the spores of eubacteria within 2–3 minutes in laboratory-scale cultures; a temperature of 121°C for 15 minutes is used to kill spores. Steam is generally used, both because bacteria are more quickly killed when moist and because steam pro vides a means for distributing heat to all parts of the sterilizing vessel. At sea level, steam must be kept at a pressure of 15 lb/sq inch (psi) in excess of atmospheric pressure to obtain a temperature of 121°C; autoclaves or pressure cookers are used for this purpose. At higher altitudes, the pressure would need to be higher than 15 psi to reach 121°C. For sterilizing materials that must remain dry, circulating hot air electric ovens are available; because heat is less effective on dry material, it is customary to apply a temperature of 160–170°C for 1 hour or more. Under these conditions (ie, excessive temperatures applied for long periods of time), heat acts by denaturing cell proteins and nucleic acids and by disrupting cell membranes. This treatment, if performed appropriately, is sporicidal.

 B. Radiation

 Ultraviolet (UV) radiation that has a wavelength of about 260 nm causes thymidine dimers resulting in the inability of bacterial DNA to be replicated. This is generally bactericidal but may not be sporicidal.

 Ionizing radiation of 1 nm or less (gamma or x-ray) causes free radical formation that damage proteins, DNA, and lipids. These treatments are both bactericidal and sporicidal.

Chemical Agents

 The chemical structures and uses of biocides are shown in Table1; selective activities of these are described in the following sections.

Table1. Some Common Biocides Used for Antisepsis, Disinfection, Preservation, and Other Purposes

Table1. Some Common Biocides Used for Antisepsis, Disinfection, Preservation, and Other Purposes (Continued)

C. Alcohols

These agents effectively remove water from biologic systems. Thus, they functionally act as “liquid desiccants.” Ethyl alcohol, isopropyl alcohol, and n-propanol exhibit rapid, broad-spectrum antimicrobial activity against vegetative bacteria, viruses, and fungi but are not sporicidal. Activity is optimal when they are diluted to a concentration of 60–90% with water. This treatment strategy is generally considered bactericidal but not sporicidal.

 D. Aldehydes

 Compounds like glutaraldehyde or formaldehyde are used for low-temperature disinfection and sterilization of instruments, endoscopes, and surgical tools. They are normally used as a 2% solution to achieve sporicidal activity. These compounds are generally bactericidal and sporicidal.

 E. Biguanides

 Chlorhexidine is widely used in hand washing and oral products and as a disinfectant and preservative. These compounds are bactericidal but not sporicidal. The mycobacteria, because of their unique waxy cell envelope, are generally highly resistant to these compounds.

 F. Bisphenols

The bisphenols are widely used in antiseptic soaps and hand rinses. In general, they have broad-spectrum microbicidal activity but have little activity against P. aeruginosa and molds. Triclosan and hexachlorophene are bactericidal and sporostatic (not sporicidal).

 G. Halogen-Releasing Agents

 The most important types of chlorine-releasing agents are sodium hypochlorite, chlorine dioxide, and sodium dichloroisocyanurate, which are oxidizing agents that destroy the cellular activity of proteins. Hypochlorous acid is the active compound responsible for the bactericidal effect of these compounds. At higher concentrations, this group is sporicidal. Iodine (I2 ) is rapidly bactericidal and sporicidal. Iodophors (eg, povidone-iodine) are complexes of iodine and a solubilizing agent or carrier, which acts as a reservoir of the active I2 .

H. Heavy Metal Derivatives

 Silver (Ag+) sulfadiazine, a combination of two antibacterial agents, Ag+ and sulfadiazine, has a broad spectrum of activity. Binding to cell components such as DNA is principally responsible for its inhibitory properties. These com pounds are not sporicidal.

 I. Organic Acids

 Organic acids are used as preservatives in the pharmaceutical and food industries. Benzoic acid is fungistatic, while propionic acid is both bacteriostatic and fungistatic. Neither is sporicidal.

J. Peroxygens

Hydrogen peroxide (H₂O₂ ) has broad-spectrum activity against viruses, bacteria, yeasts, and bacterial spores. Sporicidal activity requires higher concentrations (10–30%) of H2 O2 and longer contact times.

 K. Phenols

Phenol and many phenolic compounds have antiseptic, disinfectant, or preservative properties. In general, these are not sporicidal.

L. Quaternary Ammonium Compounds

These compounds have two regions in their molecular structures, one a water-repelling (hydrophobic) group and the other a water-attracting (hydrophilic) group. Cationic detergents, as exemplified by quaternary ammonium compounds (QACs), are useful antiseptics and disinfectants. QACs have been used for a variety of clinical purposes (eg, preoperative disinfection of unbroken skin) as well as for cleaning hard surfaces. They are sporostatic; they inhibit the outgrowth of spores but not the actual germination process. QACs have an effect on enveloped but not nonenveloped viruses. In general, these are not sporicidal.

M. Vapor-Phase Sterilants

 Heat-sensitive medical devices and surgical supplies can be effectively sterilized by vapor-phase systems using ethylene oxide, formaldehyde, hydrogen peroxide, or peracetic acid. These are sporicidal.

اخر الاخبار

اخبار العتبة العباسية المقدسة

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متحف الكفيل: نعتمد معايير علمية دقيقة في آليّة الخزن والترميم للمقتنيات المتحفية

العتبة العباسية المقدسة تناقش مع العتبة العسكرية المقدسة سبل الحفاظ على الإرث التراثي

الآخبار الصحية

تغيير بسيط في نمط التفكير قد يحدث فرقا كبيرا لصحة الدماغ ؟

لماذا ينعشنا المشروب الساخن في الطقس الحار؟

علماء يكتشفون فئة دم فريدة من نوعها في العالم !

لماذا ينصح الأطباء بزيت الزيتون يوميا؟

الآخبار التكنلوجية

حساس الإطارات.. ما هو وعلامات تلفه وكيفية صيانته؟

ما معنى أودي Quattro؟ سر الأداء والتميز الهندسي ؟!

فصل الشاحن أم الهاتف أولا؟.. عادات بسيطة تطيل عمر البطارية

تعود للقرن الرابع قبل الميلاد.. اكتشاف بقايا "إيمت" المصرية

مواضيع ذات صلة

Microbial Metabolism: Focal Metabolites and Their Interconversion

Relationship of Biocide Concentration and Time on Antimicrobial Killing

Flow cytometry

البروتوبلازم Protoplasm

غشاء الخلية The cell membrane

مملكة البدائيات (Monera)

كيس الصفار ( المح ) Yolk sac

اقسام البيئة البحرية

بيئة المياه البحرية

المياه الجارية

المياه الساكنة

بيئة المياه العذبة