Mod. 14 Control of Growth

Principles of Microbial Control

Sterilization

Commercial Sterilization

Disinfection

Antisepsis

Degerming

Sanitization

Sterilization

Kills all forms of life and destroys endospores + viruses

Commercial Sterilization

Sufficient heat treatment to destroy endospores of C. botulinum in canned foods

Disinfection

Destruction of living tissues

Antisepsis

Disinfection of living tissue

Degerming

Removal of microbes from a limited area

Sanitization

Lowering the number of microbes

Factors the influence cell death and rate

Number of microbes - more than takes longer

Microbial characteristics - endospores, mycolic acid

Environmental - if pressure of organic matter which inhibits chemical; part of biofilm

Time of exposure

Actions of control agents on

Plasma membrane

Proteins

Nucleic Acid

Physical methods of control

Moist heat

Dry heat

Filtration

Low Temperatures

Dessication (drying)

Osmotic pressure

Radiation

Moist heat

Autoclaving

Pasteurization

Autoclaving

sterilization

121C at 15psi for 15 minutes

Kills/destroy all microbes/endospores due to high temp, denaturing proteins/destroying membranes

Used for liquids (esp. large volumes) and other items

Pasteurization

Lower temp → longer time (63C for 30min)

High temp → short time (72C for 15sec)

Ultra high temp → 140C for 5 sec

Not Sterile

Used for food products

Dry heat

Flaming - 1200C

Incineration - 1000C

Hot-air sterilization

• 170C for 2 hrs

• Used for glassware - no liquids

Filtration

Physical removal of microbes

Use for materials that can’t have heat sterilization

Membranes

• 0.45 um pores for most bacteria

• 0.22 um pores for all bacteria

• 0.01 um pores for viruses

Low temperatures

1. 0-7C (fridge temp)

2. Bacteriostatic

3. No effect on psychrotrophs

Dessication (drying

Without water metabolism shuts down growth - but remain viable

Some species are very sensitive → Treponema and Neisseria gonorrhoeae

Some are very resistant - Mycobacterium since they have mycolic acid

Osmotic pressure

Plasmolysis

Add salt or sugar to foods

Less effect on mold and yeast

Radation

Ionizing

Nonionizing

Ionizing

Gamma or X-rays

<1 nm wavelength but high energy

Damages DNA

High-energy electron beam - for meats?

Nonionizing

UV light

260 nm wavelength

Damages DNA - thymine dimes

Used for surface sterilization

Products for chemical microbial growth control

Disinfectant

Antiseptic

Disinfectant

Product that does destruction of vegetative pathogens on inanimate objects

Antiseptic

Product that does destruction of vegetative pathogens on living tissue

Measurement of activity with chemical microbial control

Use-dilution test

Filter paper method

Use-dilution test

Dunk metal rings into bacteria

Dunk rings into product

Move rings to growth media

Types of chemical microbial growth control

Phenol/Phenolics (derivative of phenol)

Bisophenols

Biguanides

Halogens

Alcohols

Heavy metals

Detergents

Acid - Anionic Sanitizers

Organic Acids

Aldehydes

Gases

Phenol/Phenolics (derivatives of phenol)

Carbolic Acid = phenol

First used by Joseph Lister - phenol

Phenol is toxic

• Carcinogen

• Neurotoxins

• Irritant

Phenolics used for surfaces, instruments, skin surfaces

Targets plasma membrane

Common phenolic - is O-phenylphenol

Bisphenols

Two phenol groups connected

Hexachlorophene - pHisoHex

Triclosan

Triclosan

Ingredient was in antibacterial soaps, toothpastes, cutting boards, etc.

• Thousands of products (started seeing these in 1997)

• Steps enzyme for fully fatty acid production

• FDA- banned use in 20176 in most products

Biguanides

Chlorhexidine

Targets plasma membrane - no spores

Less toxic than phenolics

Used for surgical scrubs

Halogens

I₂

• Binds amino acids like tryosine and targets plasma membrane

• Effective against many endospores

• Antiseptic as iodophor

Cl₂

• Must combine with water → hypochlorous acid

• Strong oxidizer of enzymes

• Swimming pools, drinking water, etc.

Florine

• Fluoride (anion) is added to water and toothpastes

• Bacteriostatic and can strengthen enamel

Alcohols

Does not destroy endospores

Denatures proteins and causes plasma membrane problems

Evaporates quickly

Skin - mostly degerming for shots

• best is 60-95% (70% is common) - higher will causes clumping of cells and less will be killed

Heavy Metals

Silver, Mercury, and Copper

Oligodynamic action - just a little bit of heavy metals needed

Silver Nitrate - eye drops for newborns - not used much at all

Metal ions denature cell proteins

Detergents

Good at mechanical removal

Emulsification of oil/dirt

Cationic detergents - disrupts membranes, called quaternary ammonium compounds (quats)

Acid - Anionic Sanitizers

Combine with detergents (to decrease surface tension) and phosphoric acid

Anion portion reacts with plasma membrane

Organic Compounds

Damage plasma membranes

Food preservatives - don’t change taste

Metabolized by humans

Aldehydes

Inactivates proteins

Glutaraldehyde - for equipment use

Embalming fluid - formaldehydes

Gases

Ethylene oxide

Denatures protein

Destroys endospores and all microbes - 4-18 hours

Toxic and explosive