Control of Bacterial Growth

1. Control of Bacterial Growth • Chemical Methods • Phenols • Halogens • Biguanides • Alcohols • Surface active agents • Aldehydes • Heavy metals • Acids & bases • Gases • Peroxygens

2. Control of Bacterial Growth • Phenols & Phenolics • Lister & carbolic acid • penetrate plasma membrane & precipitate proteins • phenol coefficient - chemical agents evaluated relative to phenol • Related to phenols are cresols one of which is the active ingredient in Lysol • Bisphenols also related to phenols but also contain halogens i.e. hexachlorophene

3. Control of Bacterial Growth • Halogens • Chlorine & drinking water • Ca(OCl)2 or NaOCl - bleach • Iodine • Betadine (Iodine and organic solvent) • Chloramines • Hexaclorophene

4. Control of Bacterial Growth Chloramine N2Cl Alternative to chlorination More stable and does not dissipate as rapidly as free chlorine. Lower tendency than free chlorine to convert organic materials into chlorocarbons (carcinogens) Lacks the distinct chlorine odor of the gaseous treatment and so has improved taste

5. Control of Bacterial Growth • Hexachlorophene • Topical anti-infective, anti-bacterial agent • often used in soaps and toothpaste • pHisoHex • Thought to be carcinogenic; may be teratogenic

6. Control of Bacterial Growth • Triclosan • Anti-bacterial • often used in toothpaste • At in-use concentrations, triclosan acts as a biocide withith multiple cytoplasmic and membrane targets • lower concentrations, appears to target fatty acid biosynthesis

7. Control of Bacterial Growth • Alcohols • 70% ethanol • isopropanol • require some water to be effective • used in conjunction with other agents

8. Control of Bacterial Growth • Biguanides • Avagard – chlorhexidine • Polyaminopropyl biguanide (PAPB) • Killing effect related to damage of plasma membrane • the polymer strands are incorporated into the membrane, which disrupts the membrane reduces its permeability • Mycobacteria and endospores are resistant

9. Control of Bacterial Growth • Biguanide, Polyaminopropyl biguanide • used for disinfection on skin and in cleaning solutions for contact lens, deodorant body sprays • Effective at low concentrations

10. Control of Bacterial Growth • Surface Active Agents • soaps - emulsification of oils increases bacterial removal - deodorant soaps contain triclocarban or triclosan • acid-anionic agents used in dairy industry • quaternary ammonium compounds - work best against G+ bacteria, less effective against G-; also kill fungi protozoa and viruses; Psuedomonas resistant

11. Control of Bacterial Growth • Aldehydes • react with a variety of organic functional groups: -NH2, -OH, -SH • Formaldehyde • Glutaraldehyde • used for embalming

12. Control of Bacterial Growth • Heavy Metals • usually toxic • Silver nitrate used on infants eyes (replaced by antibiotics) • Copper sulfate used as algicide • Mercury toxicity and resistance • Zinc chloride and oxide in toothpaste

13. Control of Bacterial Growth • Acids and Bases • pH extremes inhibit growth of bacteria • acid (pickles and tomatoes) • trisodium phosphate in detergent • Propionic acid in bread • Benzoic acid in soft drinks

14. Control of Bacterial Growth • Gases • ethylene oxide - strong oxidizer and alkylating agent • very penetrating • possible carcinogen • does not damage instruments but expensive to use

15. Control of Bacterial Growth • Peroxygens - Oxidizing Agents • Ozone - being used in water treatment • Hydrogen peroxide -surface disinfecting • Benzoyl peroxide - skin treatment • Peracetic acid - used in food processing because residue is non-toxic