Transcript Inhibiting Microbial Growth in vitro

Inhibiting Microbial
Growth in vitro
CLS 311: Basic Microbiology
Mrs. 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.
2.
3.
4.
5.
6.
7.
Heat (Dray heat, Moist heat, Autoclave)
Cold.
Desiccation.
Radiation.
Ultrasonic waves.
Filtration.
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 Method
I- 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 Method
I- 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 Method
I- HEAT
3. Autoclave
• It is a large
metal chamber that uses
steam under pressure for
sterilization (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 Method
II- 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.
Physical Method
II- Cold
• 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 Method
III- 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 Method
IV- 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 Method
IV- Radiation
A. Ionizing Radiation (Sterilize)
• Gamma rays, X-rays, and Beta rays from radioactive
materials have short wavelengths (less than 1
nanometer)
Is it safe to
• 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.
humans
working,
and
consuming
these
products??!
• Irradiation has been used for many years to control
microorganism on herbs, vegetables, meat.
Physical Method
IV- 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 Method
IV- 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 Method
V- 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 Method
VI- 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 Method
VI- Filtration
HEPA
Physical Method
VII- 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
Disinfectants
A disinfectant is a chemical
agent that is used to inhibit
Antiseptics
An antiseptic is a chemical
microbial growth on inanimate
agent that is used to inhibit
objects, surfaces, and floors.
microbial growth on human
skin and mucous membranes.
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
Phenol & Phenol
Derivatives
Alcohols
Example
Uses
Lysol
Widely used to disinfect inanimate
objects.
Ethanol or
Isopropanol
Antiseptics for skin
Disinfectant for treating instruments.
Halogens
Chlorine & Iodine
Aldehydes
Formaldehyde and
Gluteraldehyde
Peroxygens
Hydrogen peroxide
•Povidone Iodine are used as
antiseptics.
•Solutions of chlorine are widely used to
disinfect surfaces, and water.
Formalin to preserve biological
specimens.
To preserve viruses in vaccines.
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