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

Pasteurizationtraditional

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 (I2)

Ca(OCl)2 calcium

hypochlorite

NaOCl sodium hypochlorite

Na dichloroisocyanurate (Chlor-Floc)

chloramine

Halogens

ChlorineChlorine gas (Cl2)

Cl2 + H2O -> HOCl hypochlorous acid

ClO2 chlorine dioxide

Oxidizing agents

Ozone (O3) 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

emulsificationsometimes 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

Ag

CuAlso: Zn, Hg, As

formaldehydeglutaraldehyde

Aldehydes

ethylene oxide propylene oxide beta-propiolactone

Gaseous chemosterilizers

Food preservativesSO2 = sulfur dioxide (and _____ bisulfite or _____ metabisulfite or _____ sulfite)

benzoic acid/Na benzoatesorbic acid/K sorbateNa nitrite & Na nitrate

Personal caremethylparaben, propylparabenmenthol

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)