9- Control of Microbial Growth

Mechanisms of action (MOA) membrane protein nucleic acid Factors number environment microbial structure/characteristics

& pseudomonads

Disinfectant evaluation Phenol coefficient American official Analytical Chemist’s use-dilution method In-use test Disk diffusion test

Heat

standard measures thermal death point (TDP) thermal death time (TDT) Decimal Reduction Time (DRT = D value)

Moist heat Steam Autoclave Pasteurization traditional High-Temperature Short-Time (HTST) Ultrahigh-Temperature treatment (UHT) UHT sterilization

Dry heat flaming oven incineration

Filtration air: High-efficiency particulate air (HEPA) liquid: porcelain & glass paper membrane

Low temperature Dessiccation Osmotic pressure

Electromagnetic radiation (4.1) Irradiated food

Phenol -> carbolic acid Lister

eugenol (clove oil) thymol pine oil

Isopropyl alcohol = isopropanol Ethyl alcohol = ethanol Proof?

tincture iodophor Halogens Iodine (I 2 )

Ca(OCl) 2 calcium hypochlorite NaOCl sodium hypochlorite Na dichloroisocyanurate (Chlor-Floc) chloramine Halogens Chlorine Chlorine gas (Cl 2 ) Cl 2 + H2O -> HOCl hypochlorous acid ClO 2 chlorine dioxide

Oxidizing agents Ozone (O 3 ) peracetic acid

Soap has a structure similar to that shown here for one type (sodium stearate). Soap works because it has the ability to interact with nonpolar (oily) substances as well as with water. In an oil droplet suspended in water, the hydrocarbon residues (R-groups) of soap molecules are immersed in the oil, and the ionic ends extend into the water. Attractive forces between water molecules and the ionic heads cause the oil droplet to be solubilized. Surfactants = Surface- Acting agents emulsification sometimes added: triclosan & triclocarban

What’s the difference?

Antibacterial soap Alcohol gel (has triclosan) Use with water Do NOT use water Scrub 2-3 minutes Wipe on, wipe off

cationic detergents = quaternary-ammonium detergents = (quats)

Oligodynamic action: heavy metals Ag CuAlso: Zn, Hg, As

formaldehyde glutaraldehyde Aldehydes

ethylene oxide propylene oxidebeta-propiolactone Gaseous chemosterilizers

Food preservatives SO 2 = sulfur dioxide (and _____ bisulfite or _____ metabisulfite or _____ sulfite) benzoic acid/Na benzoate sorbic acid/K sorbate Na nitrite & Na nitrate Personal care methylparaben, propylparaben menthol

crystal/gentian violet methylene blue Dyes Antibiotics (not used for treatment) nisin natamycin = pimaricin Other antimicrobials tea tree oil (terpin-4-ol ) manuka honey (methylglyoxal)