Chapter 5; Control of Microbial growthBio 261

Medgar Evers CollegeProf. Santos

Terms and definitions

• Sterilization- the process of removing completely all microorganisms on or in a product

• Sterile item- is free of microbes including endospores and viruses.

• Disinfection- the removal of most or all pathogens on or in a material. Generally implies the use of an antimicrobial chemical.

• Disinfectants- antimicrobial chemicals used on inanimate objects. They can also be called germicides because they target bacteria, viruses, fungi and endospores.

• Bactericidal- these target bacteria

• Antiseptics- a disinfectant that is formulated for use on the skin.

• Pasteurization- brief heat treatment to reduce the number of spoilage organisms

Deciding which method of control to use!

• This depends on several factors!!

• These factors include the situation and degree of control needed!

SITUATIONS!

1- Daily life

2-Hospitals

3-Microbiology laboratory

4-food and food product facilities

5-Water treatment facilities (chlorine and consequence of disinfectant by products)

Factors that affect our selection of an antimicrobial procedure

1- type of microorganism present. The following organisms require special consideration due to high resistance; bacterial endospores, protozoan cysts and oocytes, mycobacterium species, pseudomonas species, naked viruses.

2 - number of microorganisms initially present.

In the canning process the decimal reduction time or D value is the time required for killing 90% of a population of bacteria under certain conditions. A one D process reduces the number of organisms by one exponent.

Example; Let’s say the D value of a certain organism is 2 minutes (D=2).

Let’s say the initial number of cells is 103, it would take 6 minutes to go down to 100 or 1 survivor!

3- environmental conditions such as pH, temp, organic materials, and presence of fat greatly influence the rate microbial growth.

4- potential risk of infection

Instruments are classified as

1. critical instruments (needles, scalpels, biopsy forceps)

2. semicritical instruments (endoscopes, endotracheal tubes.

3. noncritical instruments (stethoscopes and blood pressure cuffs.

Potential risk of infection1. _______ items come into direct contact with body tissues.Critic

al

2. ____________ items come into contact with mucous membranes, but do not penetrate body tissues.

Semicritical

Surgical instruments

needles

Biopsy forceps

Respiratory equipment

Vaginal speculum

Anal proctoscope

3. ____________ items only touch keratinized skin surfaces.Noncritical

stethoscope

Sphygmomanometer (blood pressure cuff)

5- composition of item• Based on the composition of the item to be

sterilized, an appropriate sterilization method must be chosen. Certain plastics are heat sensitive so they must be treated with an antimicrobial chemical agent or it can be irradiated.

• Some moisture sensitive material can’t be treated with chemicals so they can be heat treated.

Processes used to control microorganisms

• These can be either physical or chemical!

Physical methods!

1- Moist heat- denatures proteins, its safe, fast and inexpensive

2- Dry heat

3- Filtration

4- Radiation

5- High pressure

Moist heat

a) Boiling destroys most bacteria, viruses, but not endospores. Boiling for at least five minutes can be used to sterilize drinking water.

b) Pasteurization- decreases the number of heat sensitive microorganisms except spore formers. Widely used to treat milk and some juices. 72 degrees for 15 secs.

Two types of pasteurization; 1-High temp short time method (HTST)2-Ultra high temp (UHT) method. This

method usually employs 140-150 degrees for several seconds and then rapidly cooled. The products are then transferred to chemically treated containers. Examples would be boxed juices and boxed milks.

Pasteurization

b. ____________: a brief heat treatment followed by rapid cooling. (Kills pathogens and reduces the number of spoilage organisms in milk, juices, wine, beer: Does not sterilize!) (1). LTLT (Low Temperature Long Term) 63°C/30 minutes *(2). HTST (High Temperature Short Term) 72°C/15 seconds

_________ (steam under pressure) (1). 15-20 psi/15-20 minutes/121°C (2). ________ equipment, media, etc. (3). used in canning procedures to destroy

Clostridium botulinum __________!

Autoclave

Sterilizes

endospores

c) Pressurized steam (autoclaving)

typical treatment is 121 degrees Celsius/15 PSI (pounds per square inch) for fifteen minutes.

Flash autoclaving

Rapid autoclaving (3 mins or so) at a high temperature of 135 degrees C.

Dry heat

a) incineration- oxidizes cell components to ashes

b) dry heat oven- oxidizes cell components and denatures proteins.

*Dry heat is less efficient due to a higher temp that is required and longer time needed.

Filtration

a) liquid filtration using a membrane filter. A liquid is passed through a filter with pores that trap microbes.

b) HEPA filters used to filter air and trap organisms larger than .3 um in diameter.

Radiation

a) Ionizing radiation includes gamma rays and x rays. These destroy DNA and possibly damages cell cytoplasmic membranes. Reactive molecules that damage cell components are produced!

*used to sterilize drugs, medical equipment, and disposable surgical supplies.

b) UV damages DNA but penetrates poorly.

Used to disinfect air, drinking water, and large surfaces and destroy microbes in spices.

High Pressure

• Pressure of over 130,000psi.

• It denatures proteins, and alters the permeability of the cell.

• Used for commercial food products.

Chemical methods!

Classes of chemicals used!

1-alcohol aqueous solutions.

2-aldehydes

3-Biquanides

4-ethylene oxide gas

5-halogens

6-metals

7-ozone

8-peroxygens

9-phenolic compounds

10-quaternary ammonium compounds

Target zone

I. Cell membrane

1.Quats

2.Biguanides

3.Phenolics

II. Proteins

1.Alcohols

2.Aldehydes

3.Metals

4.Halogens

5.Peroxygens

6.Phenolics

7.Ozone

III. DNA

1.Ethylene oxide gas

2.Aldehydes

Uses of each chemical method

1- alcohol, aqueous solutions are used to degerm skin and disinfect instruments.

2- aldehydes, used as preserve biological specimens, sterilize medical equipment, and formalin is used in vaccine production.

3- Biguanides are used as antiseptics in soap and lotions and impregnated into catheters and surgical mesh.

• Example; chlorhexidine

4- ethylene oxide gas is used to sterilize medical devices.

5- halogens such as solutions of chlorine are used to disinfect inanimate objects, surfaces, waste water and drinking water.

6- metals are used in topical dressing to prevent infection.

7- Ozone is used to disinfect waste water and drinking water

8- peroxides are used to sterilize containers for juices and milk and disinfect medical devices.

9-phenolic compounds are found in a variety of personal care products such as toothpaste, lotions, and deodorant soaps.

Example; Triclosan in toothpaste, lotions and soaps

Example; Hexachlorophene (nabac) is potent against S. aureus but causes nerve damage

10- Quaternary ammonium compounds are used to disinfect inanimate objects and preserve nonfood substances.

These are cationic detergents that reacts with membranes destroying vegetative cells and envelope viruses.

Preserving perishables

• Chemical

• Low temp storage such as refrigeration and freezing

• Reducing the amount of water by using salt.

Chemical preservatives

• Examples are benzoic acid, sorbic acid, propionic acid, quaternary ammonium compounds, thimerosal, nitrate, and nitrite.