Control of microbial growth means "Preventing the

growth of microbes“

OR

Preventing growth of undesirable microorganisms

Very important in microbiology experiments

Control

Killing microorganisms

Preventing their growth

The control of microbial grwoth may involve:

Sterilization

o a process that destroys all viable microbes, including microbial

cells & endospores.

oUsually done by steam under pressure or a sterilizing gas such as ethylene oxide.

oA sterilizing agent is called a sterilant.

Disinfection: Control directed at destroying harmful

microorganisms is called disinfection. It usually refers to the

destruction of vegetative (non-endospore-forming) pathogens,

which is not the same thing as complete sterility. Disinfection

might make use of chemicals, ultraviolet radiation, boiling

water, or steam. In practice, the term is most commonly

applied to the use of a chemical (a disinfectant) to treat an inert

surface or substance.

When this treatment is directed at living tissue, it is called

antisepsis, and the chemical is then called an antiseptic.

Therefore, in practice the same chemical might be called a

disinfectant for one use and an antiseptic for another.

There are modifications of disinfection and antisepsis. For example, when someone is about to receive an injection, the skin is swabbed with alcohol-this process is called as degerming.

Degerming results in the mechanical removal rather than the killing the microbes in a limited area.

Sanitization – Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels.

For example, restaurant glassware and tableware are subjected to sanitization, which is intended to lower microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another. This is usually accomplished by high-temperature washing or washing in a sink followed by a dip in a chemical disinfectant .

Names of treatments that cause the death of microbes have the suffix -cide,

meaning kill. A biocide, or germicide, kills microorganisms (usually with

certain exceptions, such as endospores); a fungicide kills fungi; a

virucide inactivates viruses.

Other treatments only inhibit the growth and multiplication of bacteria; their

names have the suffix -stat or -stasis, meaning to stop or to steady, as in

bacteriostasis. Once a bacteriostatic agent is removed, growth might

restart.

Sepsis, from the Greek, indicates bacterial contamination, as in septic

tanks for sewage treatment.

Aseptic means that an object or area is free of pathogens. Aseptic

techniques are important in surgery to minimize contamination.

CELLULAR TARGETS OF CONTROL

1. Alteration of Membrane Permeability:

A microorganism's plasma membrane is the target of many microbial control agents. This membrane actively regulates the passage of nutrients into the cell and the elimination of wastes from the cell.

Damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak into the surrounding medium and interferes with the growth of the cell.

2. Damage to Proteins and Nucleic Acids:

Antimicrobial agents denature the proteins in the microbial

cells (break the covalent & hydrogen bonds), leads to the

inactivation of enzymes which are vital to all cellular activities.

Exposure to heat, radiation or chemicals damage the nucleic

acids which leads to death of microbial cell because the cell

can no longer replicate, nor can it carry out normal metabolic

functions such as the synthesis of enzymes.

Physical methods

Chemical methods

PHYSICAL METHODS

Heat

Filteration

Low temperatures

High Pressure

Desiccation

Radiation

HEAT

Used to sterillze laboratory media, glassware and hospital instruments. Heat appears to kill microorganisms by denaturing their enzymes; the resultant changes to the three-dimensional shapes of the proteins & inactivating them.

Moist Heat Sterilization

Dry Heat Sterilization

Heat resistance varies among different microbes; these differences can be expressed through the concept of following terms:

Thermal death point (TDP)

The lowest temperature at which all the microorganisms in a particular liquid suspension will be killed in 10 minutes.

Thermal death time (TDT)

The minimal length of time for all bacteria in a particular liquid culture to be

killed at a given temperature.

Decimal reduction time (DRT, or D value)

The time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed.

MOIST HEAT STERILZATION

use of hot water or steam

Vegetative cell with in 2-3 mins

endospores 2-3 hours

Autoclave

Pasteurization

Boiling

Boiling:

Boiling kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores with in about 10 minutes.

Endospores and some viruses however, are not destroyed this quickly. Some hepatitis viruses, for example, can survive up to 30 minutes of boiling, and some bacterial endospores can resist boiling for more than 20 hours.

The use of boiling to sterilize glass baby bottles is a familiar example.

Autoclave:

Sterilization at high pressure and temperature (15psi, 121°C for

15 minutes).

Kills vegetative cells and endospores.

As the pressure increases, the temperature also increases in

autoclave.

Autoclaving is used to sterilize culture media, instruments,

solutions, syringes,transfusion equipment, and numerous other

items that can with stand high temperatures and pressure.

Pasteurization:

The technique used to kill the microbial number to minimum level with our affecting the quality of milk products. In this technique high temperature for short time is given to the milk products. The mechanism involves the treatment of milk

products at 72°C for 15 sec, this is called flash method.

In case of batch method, the milk is provided 63-66degree Celsius for about 30 minutes.

Ultra temperature method involves the treatment of milk products at 134 degree Celsius for 1 to 2 sec.

Products other than milk, such as ice cream, yogurt, and beer, all have their own pasteurization times and temperatures, which often differ considerably.

DRY HEAT STERILZTION

One of the simplest methods of dry heat sterilization is direct flaming. The familiar example is the sterilization of inoculating loops in microbiology laboratory.

Another form of dry heat sterilization is hot-air sterilization. Items to be sterilized by this procedure are placed in an oven. Generally, a temperature of about 170°C maintained for nearly 2 hours ensures sterilization .

Filteration:

Filtration is the passage of a liquid or gas through a screen like material with pores small enough to retain microorganisms.

This method is used for heat sensitive liquids to remove microbes.

Hospital isolation units and research laboratories HEPA filters are used to filter microbes.

Membrane filters, also have become popular for industrial and laboratory use.

LOW TEMPERATURES

Microbiostatic- Slow growth of microbes

Refrigeration 4°C Static, except for psychrotrophs

short term food preservation

Freezing –20°C or lower

static to many microbes

long term food preservation (-20°C) or specimen storage (-80 to -196°C).

HIGH PRESUURE High pressure applied to liquid suspensions is transferred instantly and evenly throughout the sample. If the pressure is high enough, it alters the molecular structures of proteins and carbohydrates, resulting in the rapid inactivation of vegetative bacterial cells.

Fruit juices preserved by high-pressure treatments have been marketed in Japan and the United States.

DESSICATION Microorganisms cannot grow or reproduce but can remain viable for years. Then, when water is made available to them, they can activate, grow and reproduce.

This is the principle that underlies lyophilization, or freeze-drying, a laboratory process for preserving microbes are the examples of dessication.

Ionizing

Radiations

Non-Ionizing

Radiations

RADIATION

Ionizing Radiation

Shorter wavelength, Highly penetrating

Break DNA backbone

used to sterilize food products and medical instruments

Gamma rays, X rays, or high –energy electron beams

RADIATION

Non-ionizing Radiation

Longer wavelength and have less penetrating power

Also disrupt DNA structure

Used to sterilize air and solid surfaces

UV Rays. A UV, or "germicidal," lamp is commonly found in hospital

rooms, nurseries, operating rooms, and cafeterias. UV light is also used to

disinfect vaccines and other medical products.

CHEMICAL CONTROL Different disinfectants are used:

1. Halogens

2. Phenolics

3. Alcohols

4. Hydrogen peroxide

5. Detergents & soaps

6. Aldehydes

7. Heavy metals

8. Antiobiotics

1. HALOGENS A group of five chemically related elements in the periodic

table

Chlorine (Cl), Florine (F), Iodine (I), Bromine (Br), Astatine

(At)

The name 'halogen' means 'salt-producing'. When halogens

react with metals they produce a wide range of salts,

including calcium fluoride, sodium chloride (common

salt), silver bromide and potassium iodide.

CHLORINE Denaturation of proteins (by disrupting Amino acids) &

inactivation of enzymes.

Chlorine is used as a disinfectant in gaseous form (Cl2 ) or

in the form of a compound, such as calcium hypochlorite,

sodium hypochlorite (NaOCl, Clorox), and chloramines.

Its germicidal action is caused by the hypochlorous acid

(HOCl) that forms when chlorine is added to water.

Used to clean the drinking water & swimming pools

IODINE

most effective antiseptics.

It is active against all kinds of bacteria, many endospores, various fungi, and some viruses.

Iodine impairs protein synthesis and alters cell membranes, apparently by forming complexes with amino acids and unsaturated fatty acids.

Iodine is available:

as a tincture- that is, in solution in aqueous alcohol

and as an iodophor. An iodophor is a combination of iodine and an organic molecule, from which the iodine is released slowly. e.g. Betadine

used mainly for skin disinfection and wound treatment.

2. PHENOLICS Derivatives of phenol, called phenolics, contain a molecule of phenol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with a soap or detergent .

Phenolics exert antimicrobial activity by injuring lipid-containing plasma membranes, which results in leakage of cellular contents.

They remain stable, and persist for long periods after application .

One of the most frequently used phenolics is derived from coal tar, a group of chemicals called cresols which are very good surface disinfectants.

3. ALCOHOL Alcohols effectively kill bacteria and fungi but not endospores

The mechanism of action of alcohol is usually protein denaturation, but alcohol can also disrupt membranes and dissolve many lipids.

Alcohol acts & then evaporates rapidly

Alcohols are unsatisfactory antiseptics when applied to wounds. They cause coagulation of layer of protein under which bacteria continue to grow.

The most commonly used alcohols are ethanol and propanol.

The recommended optimum concentration of ethanol is 70%, but concentrations between 60% and 95% seem to kill as well.

Pure ethanol is less effective than aqueous solutions (ethanol mixed with water) because denaturation requires water.

4. HYDROGEN PEROXIDE Not a good antiseptic for open wounds. It is quickly broken down

to water and gaseous oxygen by the action of the enzyme catalase, which is present in human cells.

Hydrogen peroxide does effectively disinfect the non-living objects.

it is even sporicidal at high concentrations.

On a nonliving surface, the normally protective enzymes of aerobic bacteria and facultative anaerobes are overwhelmed by high concentrations of peroxide.

The packaging material passes through a hot solution of the chemical before being assembled into a container.

Also used as a disinfectant for contact lenses, sometimes,it might cause eye irritation.

Heated hydrogen peroxide can be used as a gaseous sterilant.

5. DETERGENTS AND SOAPS

Detergents

They solubilize the cell wall

Antiseptic and disinfectant

Not sporicidal

Soaps

Mechanically remove particles containing microbes

and oil from the skin

6. ALDEHYDES Aldehydes are among the most effective

antimicrobials. Two examples arc formaldehyde and glutaraldehyde. They inactivate proteins by forming covalent cross-links with several organic functional groups on proteins.

Formaldehyde:

o Formaldehyd gas is an excellent disinfectant. However, it is more commonly available as formaline, a 37% aqueous solution of formaldehyde gas.

o Formalin is used extensively to preserve biological specimens such as human dead bodies.

6. ALDEHYDES Glutaraldehyde :

o is used to disinfect hospital instruments, including endoscopes and respiratory therapy equipment.

o When used in a 2% solution (Cidex), it is bactericidal, tuberculocidal, and virucidal in 10 minutes and sporicidal in 3 to 10 hours.

o Glutaraldehyde is one of the few liquid chemical disinfectants that can be considered a sterilizing agent.

7. HEAVY METALS Heavy metals can be biocidal or antiseptic, including silver,

mercury, and copper.

The ability of very small amounts of heavy metals, especially silver and copper, to exert anti microbial activity is referred to as oligodynamic action.

Egyptians found that silver coins in water barrels served to keep the water clean of unwanted organic growths.

This action can be seen when we place a coin or other clean piece of metal containing silver or copper on a culture on an inoculated Petri plate.

Silver nitrate: used to cure eye infections in new born babies.

Copper Sulfate: to retard the growth of algae in swimming pools

8. ANTIBIOTICS Antibiotics are used in food preservation.

Nisin, is often added to cheese to inhibit the growth of certain endospore forming spoilage bacteria.

Nisin is present naturally in small amounts in many dairy products. It is tasteless, readily digested, and nontoxic.

Natamycin is an antifungal antibiotic approved for use in foods, mostly cheese.

Microbes are found everywhere in environment

Their control is most important By killing

By stopping Growth

Microbial Death refers to complete loss of reproductive ability of microbes even under optimum conditions

Different Methods to control Physical Methods

Chemical Methods

INTERESTING FACT!!!!!

Deinococcus radiodurans can withstand blasts of radiation 1,000 times greater than what would kill a human being.