Control of MicroorganismsControl of Microorganisms

Control of Microbial GrowthControl of Microbial Growth

Effected in two basic ways:

1. By Killing Microorganisms

2. By inhibiting the Growth of Microorganisms

Usually involves the use of:

1. Physical Agents

2. Chemical Agents

Principles of Microbial Control Principles of Microbial Control (Definitions)(Definitions)

• Prevention / Control of Growth to Prevent Infection and Spoilage

Principles of Microbial Control Principles of Microbial Control (Definitions)(Definitions)

• Sterilization / Complete Destruction

- No degrees of sterilization (All or Nothing)

-

Principles of Microbial ControlPrinciples of Microbial Control

• Disinfection / Reducing Growth Nonliving Surfaces

Principles of Microbial ControlPrinciples of Microbial Control• Antisepsis / Reducing Growth on Living

Tissue

Principles of Microbial ControlPrinciples of Microbial Control

• Antisepsis / Reducing Growth on Living Tissue

• Antiseptics are generally less toxic than disinfectants because they must not cause too much damage to the host living tissue. Examples of antiseptics include iodine, 70% ethanol and 3% hydrogen peroxide.

Principles of Principles of Microbial Microbial ControlControl

• Sanitize

Subject to High Temperature Washing (Dishwashers)

Principles of Microbial ControlPrinciples of Microbial Control

• Cide – Suffix Meaning to Kill

• Stat – Suffix Meaning to Inhibit

• Sepsis – Bacterial Contamination

• Asepsis – Lack of Bacterial Contamination

Time to Kill in Proportion to the Time to Kill in Proportion to the Population SizePopulation Size

• Large Numbers Require Greater Time• Small Numbers Require Less Time

Susceptibilities VarySusceptibilities Vary

• Endospores are Difficult to Kill• Organic Matter May Interfere with Heat

Treatments and Chemical Control Agents

Control Agents Act ByControl Agents Act By

• Alteration of Membrane Permeability

- Susceptibility of membrane is due to its lipid and protein composition

- Control Agents can alter permeability• Damage to Proteins and Nucleic Acids

- Break hydrogen and covalent bonds in proteins

- Interfere with DNA, RNA, Protein

Synthesis

Types of methods

• Physical

• Chemical

Physical Methods of Microbial Physical Methods of Microbial ControlControl

Physical Physical MethodsMethods

• Heat

• Filtration

• Low Temperatures

• Desiccation

• Osmotic Pressure

• Radiation

HeatHeat

• Most Frequent and Widely Used.

• 1. Type of Heat– Moist

– Dry

2. Time of Application

3. Temperature

• Thermal Death Point (TDP) / Lowest Temp to Kill All the Bacteria in a Broth in 10 Minutes

• Thermal Death Time (TDT) / Time Span Required to Kill All the Bacteria in a Broth at a Given Temperature

• Decimal Reduction Time (DRT) / Length of Time in Which 90% of a Bacterial Population will be Killed at a given Temperature

• Boiling / Kills Many Vegetative Cells and Inactivates Viruses Within 10 Minutes

Moist Heat SterilizationMoist Heat Sterilization• Boiling• Autoclaving

BoilingBoiling

• 100° C for 30 Minutes

• Kills Everything Except Some Endospores

AutoclavingAutoclaving• Steam Under

Pressure• 121° C for 15

Minutes at 15 lb/in2

• Heat-labile Substances will be Denatured

• Steam Must Contact the Material

Dry Heat SterilizationDry Heat Sterilization• Direct Flaming• Incineration• Hot-Air Sterilization (Oven)

Flaming the Loop

Flaming the loop helps to prevent contamination of the bacteria.

When flaming the loop, make sure that all of the wire has been heated to redness.

IncinerationIncineration

• Burns and Physically Destroys Organisms

• Used for

a. Needles

b. Inoculating Wires

Dry Heat (Hot Air Oven)Dry Heat (Hot Air Oven)

• 160° C for 2 Hours or 170° C for 1 hour

• Used for

a. Glassware

b. Metal

c. Objects That Won’t Melt

PasteurizationPasteurization• A High Temperature

Is Used For a Short Time

• Batch Method– 63°C for 30 Minutes

– 71 for 15 seconds

• (UHT) sterilization 140°C for 3 seconds. – 2 months with only

minimal changes in flavor.

FiltrationFiltration• The passage of a liquid or gas through a filter with

pores small enough to retain microbes.• Especially important to sterilize solutions which

would be denatured by heat (antibiotics, injectable drugs, amino acids, vitamins.)

HEPA FiltersHEPA Filters• HEPA filters are High-Efficiency Particulate Air

filters designed for the filtration of small particles. Certified HEPA filters must capture a minimum of 99.97% of 0.3 microns contaminants.

Low TemperaturesLow Temperatures

• Decreasing Temperature

Decreases Chemical Activity

• Low Temps are Not Bactericidal

DesiccationDesiccation

• Disrupts Microbial Metabolism• Stops Growth / Microbes Are Still Viable• Freeze-drying / Dehydration

• Viruses and Endospores Can Resist Desiccation

Osmotic PressureOsmotic Pressure

• Plasmolysis

• Sugar Curing / Salting

• May Still Get Some Mold or Yeast Growth

RadiationRadiation

• Ionizing Radiation

1. High Degree of

Penetration

2. Examples

- Gamma Rays

- X-rays

- High Energy

Electron Beams

• NonIonizing Radiation

1. Low Degree of Penetration

2. Harmful / Skin / Eyes

3. Cell Damage / Thymine

4. Germicidal / 260 nm

5. Example: Ultraviolet

Ionizing RadiationIonizing Radiation• Ionizing radiation (gamma radiation) can

penetrate deeper into objects, and is used to sterilize food, drugs, and medical supplies

Chemical Control MethodsChemical Control Methods

• Phenols and Phenolics• Halogens• Alcohols• Heavy Metals and Their Compounds• Surface-Active Agents• Quaternary Ammonium Compounds• Chemical Food Preservatives• Aldehydes

Types of DisinfectantsTypes of Disinfectants

• Phenol and Phenolics

- Exert Influence By

1. Injuring Plasma membranes (lipids)

2. Inactivating Enzymes

3. Denaturing Proteins

Not effective against spores

Types of Types of DisinfectantsDisinfectants

• Halogens- Can be Used Alone or in Solution- Chlorine -- Purifies Drinking Water

a. Forms an Acid Which is Bactericidalb. Disinfectant in Gaseous Form or in Solution as Calcium Hypochlorite

Types of DisinfectantsTypes of Disinfectants

• Halogens- Iodine – combines with Amino Acids

a. Inactivates Enzymesb. Tincture / Alcohol

Types of Types of DisinfectantsDisinfectants

• Alcohols

- Denature Proteins

- Dissolve Lipids

- Tinctures

- Wet Disinfectants

a. Aqueous Ethanol (60% - 95%)

b. Isopropal Alcohol

Types of DisinfectantsTypes of Disinfectants

• Heavy Metals and Their Compounds

- Used for Burn Treatment

- Prevents Neonatal Gonorrheal Opthalmia

- Denature Proteins

- Example / Silvadene Ointment / Silver

Types of DisinfectantsTypes of Disinfectants

• Surface-Active Agents

- Decrease Molecular Surface Tension

- Include Soaps and Detergents

- Soaps Have Limited Germicidal Action but

Assist in the Removal of Organisms by Scrubbing

- Acid-Anionic Detergents / Dairy

Types of Types of DisinfectantsDisinfectants

• Quaternary Ammonium Compounds (QUATS)

- Cationic Detergents Attached to NH4

+1

- Disrupt Plasma Membranes

- Most Effective on Gram-Positive Bacteria

- Mouthwashes and Sore Throat Remedies

Types of Types of DisinfectantsDisinfectants

• Chemical Food Preservatives

- Sorbic Acid

- Benzoic AcidInhibitFungus

- Propionic Acid

- Nitrate and Nitrite Salts / Meats /

To Prevent Germination of Clostridium botulinum endospores

Types of Types of DisinfectantsDisinfectants

• Aldehydes

- Formaldehyde

- Glutaraldehyde

- Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH)

Antibiotics• Cell wall antibiotics

• Bactracin

• Cycloserine

• Vancomycin

• Penicillin and beta lactam antibiotics Cell menbrane antibiotics

• DNA Synthesis Inhibitors

• RNA Synthesis Inhibitors

• Protein Synthesis Inhibitors

• Metabolism