Inhibiting Microbial Growth in vitro

CLS 311: Basic MicrobiologyMrs. Amany Ahmed Niazy

Microbicidal or Microbistatic?

Microbicidal Microbicidal is the process or an agent that kills the

microorganism. • The suffix -cidal or –cide means ''killing''.

Microbistatic Microbistatic is the process or an agent that inhibits

the growth and reproduction of the microorganism. • The suffix -static or –state means ''inhibiting or

stopping''.

Cleansing

Cleansing is the removal of organic material from instruments and equipment & may be done, clinically, in four steps:

Rinsing the object under cold water

Applying detergent and scrubbing object

Rinsing the object under warm water

Drying the object prior to sterilization or disinfection

Sterilization or Disinfection?

Sterilization Sterilization is the complete destruction of all forms

of microbial life including bacteria, viruses, fungi, parasites, and spores.

Disinfection Disinfection is reducing or eliminating the number

of pathogenic microorganisms to the point where they no longer cause disease. But this method does not affect spores.

Pasteurization and Sanitization

Pasteurization Is a disinfecting method used to eliminate

pathogens from liquids e.g. milk, juice,..

Sanitization Is the use of chemical agents on food-handling

equipment to meet public health standards and minimize chances of disease transmission e.g. use of hot water & soap in cleaning restaurants.

STERILIZATION AND DISINFECTION METHODS

Methods used to destroy or inhibit microorganisms are either physical or chemical, and sometimes both types are used.

Physical Methods

Physical Methods• They are commonly used in hospitals, clinics, and

laboratories. Physical methods include:

1. Heat (Dray heat, Moist heat, Autoclave)2. Cold.3. Desiccation.4. Radiation.5. Ultrasonic waves.6. Filtration.7. Gaseous atmosphere.

Physical Method I- HEAT

• Heat is considered the most common method for sterilization because it is practical, efficient, and inexpensive.

• Heat kills microorganisms by denaturing their enzymes and other proteins.

• There are three methods of sterilization or disinfection by heat:

• dry heat • moist heat• autoclave.

Physical MethodI- HEAT

1. Dry Heat

• An effective way to sterilize metals, glassware, some powders, oils, and waxes.

1. Hot Air Oven: It is done in a 160-165°C oven for 2hours or in 170-180°C oven

for 1hour.

2. Burning (incineration): Is used to destroy contaminated disposable materials.

3. Direct Flame: Bunsen burner or electrical heating device is used to sterile wire

loops and forceps used in the laboratory.

Dry heat Oven

Bunsen Burner

Electric Bunsen

Physical MethodI- HEAT

2. Moist Heat

• Is used to disinfect syringes, needles, and simple instruments by boiling (100°C) for 30 minutes.

• Boiling is not always effective as spores, like Mycobacteria, and some viruses are not affected.

Physical MethodI- HEAT

3. Autoclave

• It is a large metal chamber that usessteam under pressure forsterilization (like the pressure cooker).

• Autoclaving is done at 121.5°C and 15psi pressure for 20 minutes.

• An autoclave tape or strip (commercially available) is used to ensure proper functioning.

Autoclave Tapes

Physical MethodII- Cold

1. Freezing (below zero) Freezing will greatly slow the metabolic

activities of microorganisms leading to inhibition of their growth.

2. Refrigeration (4°C) Refrigeration will slightly affect the metabolic

activities of most microorganisms but it would not completely inhibit growth. It will slow down their growth.

• Slow Freezing is the most effective way as ice crystals that forms may rapture the cell membrane and cell wall of microbes.

• CAUSION: Thawing and refreezing of food will allow the bacteria and its spores to resume growing.

Physical MethodII- Cold

Physical MethodIII- Desiccation (Drying)

• Many microorganisms stay viable even after drying but they cannot reproduce i.e. desiccation will inhibit the growth of microorganisms.

• When suitable moist and nutrient rich environment is available, the microorganism will grow rapidly.

• It is often used for preservation of food, antisera, antitoxin, antibiotics, and pure culture of microorganisms.

Keep in mind that dried viable pathogens may

be found in blood, pus, fecal material and dust

that are found on floors , in bedding, on

clothing. Thus wet mopping of floors, damp

dusting of furniture rolling bed linens an towels

carefully, is very important to avoid

transmission of these microbes through air .

Physical MethodIV- Radiation

• There are three different types of radiation that can be used to control microorganisms:

A. Ionizing radiation.B. Ultraviolet radiation.C. Microwave radiation.

Physical MethodIV- Radiation

A. Ionizing Radiation (Sterilize)

• Gamma rays, X-rays, and Beta rays from radioactive materials have short wavelengths (less than 1 nanometer)

• Cause death or mutations in microorganisms as they damage the DNA and proteins.

• Used to sterilize heat-sensitive materials including medical equipment, disposable surgical supplies and drugs. Radiation can be carried out after packaging.

• Irradiation has been used for many years to control microorganism on herbs, vegetables, meat.

Is it safe to

humans

working,

and

consuming

these

products!??

Physical MethodIV- Radiation

B. Ultraviolet light (Non-ionizing Radiation)(disinfect)

• Wavelength is longer than 1 nanometer low penetration. • Damages DNA which cause mutations or death.

• Most effective on actively multiplying organisms.

• Endospores are the most UV-resistant.

• Most commonly used as UV-lamps that disinfect to destroy microbes in the air or drinking water and to disinfect surfaces.

• Disadvantages: Damages skin, eyes and does not penetrate paper, glass, and cloth.

UV-Lamps

Physical MethodIV- Radiation

C. Microwave Radiation Do not affect microorganisms directly, but kill

microbes by the heat they generate in an item.

Organisms often survive microwave cooking, however, because the food heats unevenly.

May kill microbial cells in moist foods but not spores.

Physical MethodV- Ultrasonic Waves

• Used for cleaning delicate equipments.

• Ultrasonic cleaners consist of water tanks, were short sound waves pass

through, where it mechanically remove organic debris.

• Eequipment must then be washed and sterilized before use.

Physical MethodVI- Filtration

• Filtration is the removal of microbes by passage of a liquid or gas through a screen like material with small pores.

• Filters of various pore sizes can be used.

• Used to sterilize heat sensitive materials like vaccines, enzymes, antibiotics, and some culture media.

• Air Filtration:High Efficiency Particulate Air Filters (HEPA):

Used in operating rooms and burn units to remove bacteria from air. Used in biological safety cabinets (laminar flow hoods)

Physical MethodVI- Filtration

HEPA

Physical MethodVII- Gaseous Atmosphere

• In rare cases, changing the atmosphere can be used as a way to inhibit the growth of microorganisms.

• Aerobes and microaerophiles can be killed by placing them in oxygen-free atmosphere. Whereas, anaerobes can be killed by placing them in oxygen atmosphere.

Chemical Methods

Chemical Methods

Antiseptics

An antiseptic is a chemical

agent that is used to inhibit

microbial growth on human

skin and mucous membranes.

Disinfectants

A disinfectant is a chemical

agent that is used to inhibit

microbial growth on inanimate

objects, surfaces, and floors.

How to Select an Appropriate Chemical ???

1. Toxicity what are the risk to humans or environment.

2. Activity in the presence of organic matter some chemicals are inactivated by organic matter.

3. Compatibility with the material being treated some corrosive like hypochlorite can damage some metals and rubber.

4. Cost and availability.

5. Storage and stability some have limited shelf life.

6. Concentration of disinfectant lose effectiveness when diluted more than the manufacturer recommendation.

7. Number and type of microorganism to be killed (or inhibited)

Groups of Chemicals Used as Disinfectant

Chemical Example UsesPhenol & Phenol Derivatives

Lysol Widely used to disinfect inanimate objects.

Alcohols Ethanol or Isopropanol

Antiseptics for skinDisinfectant for treating instruments.

Halogens Chlorine & Iodine•Povidone Iodine are used as antiseptics.•Solutions of chlorine are widely used to disinfect surfaces, and water.

Aldehydes Formaldehyde and Gluteraldehyde

Formalin to preserve biological specimens.

To preserve viruses in vaccines .

Peroxygens Hydrogen peroxide Personal care products, like lotions, deodorant soaps.

Resistance to Killing Gram-negative bacteria (with their outer membrane) are generally more

resistant than gram-positive bacteria to disinfectants and antiseptics

Stationary-phase (I.e., non-growing) bacteria generally are more resistant than log-phase (I.e., growing) bacteria

Mycobacteria, endospores, and protozoan cysts and oocysts are very resistant to disinfectants and antiseptics

Nonenveloped viruses are generally more resistant than enveloped viruses to disinfectants and antiseptics

Organic matter (such as vomit and feces) frequently affects the actions of chemical control agent

Disinfectant activity is inhibited by cold temperatures

Longer application times are preferable to shorter

Those humans are starting to annoy me