Control of Microorganisms Control of Microorganisms Various Physical & Chemical Various Physical & Chemical

MethodsMethods

Many microorganisms are beneficial.Many microorganisms are beneficial.

Some are harmful.Some are harmful.

Microbial activities – food spoilage and disease.Microbial activities – food spoilage and disease.

Introduced concept of microbial controlIntroduced concept of microbial control

Ignaz Semmel Weis Ignaz Semmel Weis [ Hungarian Physician ][ Hungarian Physician ]

Joseph Lister Joseph Lister [ English Physician][ English Physician]

Microbial growth controlled by Microbial growth controlled by physicalphysical & & chemicalchemical methods. methods.

Kill or inhibit growth.Kill or inhibit growth.

TERMINOLOGY RELATED TO THE CONTROL OF MICROBIAL GROWTH

• Sterilization: A treatment that kills or removes all living cells, including viruses and spores, from a substance or object.

• Disinfection: A treatment that reduces the total number of microbes on an object or surface, but does not necessarily remove or kill all of the microbes (Chlorination).

• Sanitation: Reduction of the microbial population to levels considered safe by public health standards.

STERILIZATION

DISINFECTANTS SANITATION

• Antiseptic: A mild disinfectant agent suitable for use on skin surfaces.

• Germicide: “the agent kills” microbes. For example, a bactericide agent kills bacteria, fungicide, virucide, sporocide.

• Bacteriostatic: “the agent inhibits growth.” For example, a fungi static agent inhibits the growth of fungi, but doesn’t necessarily kill it.

( Refrigeration) • Degerming: Removal of microbes from skin.• Antimicrobial Agent: Agent kills micro

-organisms or inhibit their growth.

ANTISEPTIC DEGERMING

BACTERIOSTATICS

Conditions influencing 1. Temperature 2. Type of Microbe 3. Physical State

Actions Kill Inhibit Microbes Damage Plasma Membrane

Gram Positive Bacteria – Disinfectants and antiseptics greater effect.

Gram Negative Bacteria – Pseudomonads grow in some disinfectants and antiseptics.

Endospores resistant to chemical agents & physical methods.

PHYSICAL METHODSPHYSICAL METHODS

• Damaging cell components.

• Enzymes, DNA, Cytoplasmic membranes disrupt.

Used in food industry.

Preparation of culture media lab ware,

sterilization of instrument.

PHYSICAL METHODSPHYSICAL METHODS

Heat

Temperature

Desiccation

Osmotic Pressure

Filtration

Radiation

HEATHEAT Kills microbes by denaturing enzymes.

Heat resistance varies among different microbes.

Thermal Death Point (TDP)

Thermal Death Time (TDT)

Decimal Reduction Time (DRT)

Thermal Thermal Death Death PointPoint

Thermal Death Point (TDP)

• Lowest temperature to kill

all the bacteria in 10 minutes.• Thermal death is useful in

purifying water.• Boiling - Kills many

Vegetative Cells.• Inactivates Viruses Within 10

Minutes • No effect on spores.

Thermal Death TimeThermal Death TimeThermal Death Time (TDT) • Time required to kill all the

bacteria at a given temperature.

• Developed for food canning.

• Applications in cosmetics and pharmaceuticals.

Decimal Reduction TimeDecimal Reduction Time

Decimal Reduction Time (DRT)

• Length of time.

• 90% of a bacterial population killed at a given temperature

• Reduces the number of organisms to 1/10 the initial level.

• Used in Commercial Sterilization.

Rate of Microbial DeathRate of Microbial Death

• Bacteria usually die at a Constant Rate .• Plotted logarithmically this will give a Straight Line

AUTOCLAVING

PASTEURIZATION

• Process used in preserving heat sensitive foods.

• Milk, beer, and other beverages. • 63 °C for 30 Minutes.• Wine - Pasteur• Milk - VH & F soxhlet .• Reduction of microorganism in milk.• Pasteurization is not a method of sterilization.

Two different process• High Temperature Short Time (HTST) process - 72°C for 15s ( Quick heating and cooling).• Ultra High Temperature (UHT) sterilization - heating at 140°C for 3 seconds. • Milk kept at room temperature for 2 months.• Minimal changes in flavor.• Equivalent Treatments – Different methods produce same effect.• Mycobacterium – Tuberculosis

Low TemperaturesLow Temperatures• Decreasing temperature decreases chemical

activity.

• Low Temperature are Not Bactericidal.

• Restrict enzyme activity.

• Ordinary Refrigerator Temperature 0° – 7°C .

• Do not Reproduce.

• Survive, Restrict rate of growth.

• Use – Food Preservation, Drug, Culture Preservation.

DRY HEAT STERILIZATION Direct Flaming – Burning contaminants

Incineration - Burns and Physically Destroys Organisms

Used for

a. Needles

b. Inoculating Wires

c. Glassware

d. Body Parts

Hot Air Sterilization – Oxidation

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

Used for

a. Objects That Won’t Melt

b. Glassware

c. Metal

FILTRATIONFILTRATION• The passage of a liquid or gas through a filter with pores

small enough to retain microbes.• Separate bacteria from suspending liquid.• Filter – Nitrocellulose, acetate.• Bacteria, virus large protein.• High efficiency particulate air filters.

• Filterable viruses.

Two types of Filters:-• Depth Filters – Fibrous or granular material.• Thick layer filled with twisting channels.• Microorganisms sucked through thick layer.• Microbes removed by physical screening.• Membrane filters – Circular filters• Porous membrane – 0.1mm thick• Made of cellulose acetate, cellulose nitrate,

polycarbonate.• Variety of pore size.

HEPA FILTERSHEPA FILTERS• HEPA filters - High-Efficiency Particulate Air Filters • Filtration of small particles.

• Capture a minimum of 99.97% of 0.3 microns contaminants.

HEPA FiltersHEPA Filters

• Filtration is the primary method of eliminating pathogens from the air supply.

1. Operating Rooms

2. Burn Units

3. Hospitals, Surgical Mask.

4. Pharmaceutical Manufacturing Facilities

DESICCATIONDESICCATION• Removing water from microbes.

• Viruses & Endospores can resist.• Disruption of metabolism.• Use – Food Preservation. • Stops Growth / Microbes are still viable.• Freeze-drying ( Lyophilization) – remove water from

specimen.• Gonorrhea bacterium – with stand for only 1 hour.• Tuberculosis bacterium – viable for months ( Mycolic acid).• Powdered milk – 85% water is removed.

OSMOTIC PRESSUREOSMOTIC PRESSURE• Plasmolysis

• High zone of salt & sugar.

• Salt – Preservation of fish, meat, food.

• High osmotic pressure.

• Low availability of sugar solution to prevent microbial growth.

• Honey, high sugar content preserved.

• Loss of H2O.

RADIATIONRADIATION Its Efficiency is Dependent on the Wavelength, Intensity, and Duration.

Two types :-

Ionizing Destruction of DNA by gamma rays & high energy electron

beams. Use –

Sterilizing pharmaceuticals medical & dental supplies.

Food preservation and other industrial processes. More penetrating. Food is exposed to high levels of radiation to kill insects,

bacteria and mold.

Non – Ionizing Damage to DNA by UV light. Effective germicide wave length 260nm. Poor penetration UV radiation is only useful for disinfecting

outer surfaces.

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• Antibiotics

Types of DisinfectantsTypes of Disinfectants Phenols and Phenolics Another Name for Carbolic Acid / Lysol / Pine-Sol

- Joseph Lister

- Exert Influence By

1. Injuring Plasma membranes

2. Inactivating Enzymes

3. Denaturing Proteins

Use – Skin surface, Environmental surface, Instruments, Mucous

membranes.

Common – Cresols, Hexachlorophene.

Phenolics are Long Lasting.

No Effect on Spores.

Effective antibacterial agents, fungi and many viruses.

CHLORHEXIDINECHLORHEXIDINE

• Damages plasma membranes.

• Use – Skin degerming, Surgical scrubs.

• Only Operates in Narrow pH Range (5-7).

HALOGENSHALOGENS Can be Used Alone or in Solution. Inactivated by Sunlight Alter cellular component. Inactive enzymes.

Chlorine - Purifies Drinking Water

- 2-4 Drops of Chlorine per Liter / 30 Min - Forms an Acid - hypochlorous acid – Bactericidal

- Gaseous form or in Solution as Calcium Hypochlorite. - Good disinfectants on clean surfaces. - Inexpensive / Chlorox. - Never Mix with Other Cleaning Agents! - Kills legionella species ( Legionella Pneumophila Bacteria ).

Iodine Least toxic of the disinfectants. Combines with Amino Acids.

a. Inactivates Enzymesb. Tincture / Alcoholc. Iodophor

Betadine Wound treatment.

ALCOHOLALCOHOL• Denature Proteins and Dissolve Lipids.

• Evaporates

• Fast Acting

• Wet Disinfectants

a. Aqueous Ethanol (60% - 95%)

b. Isopropyl Alcohol

• Not effective against endospore.

• Use – Thermometer, Instruments, before

injection swabbing skin.

HEAVY METALSHEAVY METALS• Silver, Mercury – germicidal or antiseptic• Silver nitrate – prevent gonococcal eye infections.• Copper sulfate – Algicide• Mercurochrome – Disinfects skin and mucus membrane.• Used for Burn Treatment

- Denature Proteins

- Example / Silvadene Ointment / Silver• Mercuric chloride – Bacteriostatic• Copper sulphate – destroy green algae in reservoirs.• Zinc chloride – ingredients in mouth washes.

• Zinc oxide – anti fungal in paints.

SURFACE ACTIVE AGENTSSURFACE ACTIVE AGENTS• Include Soaps and Detergents.

• Soaps – Anionic detergents.

• Skin degerming.

• Triclocarbon – inhibit gram positive bacteria.

• Decrease Molecular Surface Tension

• Limited Germicidal Action.

• Removal of Organisms by Scrubbing.

CATIONIC DETERGENTSCATIONIC DETERGENTS

• Quaternary Ammonium Compounds (QUATS)

- Cationic Detergents Attached to NH4+

- Disrupt Plasma Membranes

- Most Effective on Gram-Positive Bacteria

• Enzyme inhibition, protein denaturation.

• Fungicide, Amoebocide.

• Two popular QUATS – Zephiran.

• Cepacol – Anti microbial

ORGANIC ACIDSORGANIC ACIDS

Chemical Food Preservatives

- Sorbic Acid

- Benzoic Acid Inhibit Fungus

- Propionic Acid

- Nitrate and Nitrite Salts / Meats

• To Prevent Germination of Clostridium botulinum endospores.

• Calcium Propionate – Bread

Aldehydes

• Antimicrobial.

• Inactivate Proteins.

• Covalent crosslink formation.

• Formaldehyde – preserve biological specimens.

• Glutaraldehyde – Sterilize hospital instruments.

• Most Effective of all Chemical Disinfectants.

• Carcinogenic.

• Oxidize Molecules Inside Cells.

Antibiotics

Used to Preserve Cheese. Used in Feed Given to Food Animals.