Download lecture NO 13 - INAYA Medical College

Infection control
L. Dalia Kamal Eldien
MSc in Microbiology
Lecture NO: 13
Introduction
 Infectious diseases can be the result of the colonization
of the body by various microbes.
 There are many similar disease states that can arise from
different causes, i.e. pneumonia can be caused by viruses,
or bacteria, or protozoa, and even fungi.
 Scientists' reasoned that if microorganisms cause disease,
then it was possible to control disease by controlling the
microorganisms.
Infection control
To control the growth of microorganisms and their
transmission of infectious disease involve:
 Stopping the growth of the microorganism for a period of
time
 Reducing the number of microorganisms to a safe level
 Destroying the microorganisms
Methods controlling the
microorganisms
For instruments, equipment,
and fluids use method known as
Sterilization and Disinfection
Sterilization
 Sterilization is defined as a freeing an object from all kinds
of living microorganisms including spores.
 Methods of sterilization, can broadly be grouped in two
1- Physical method
2- Chemical method (Disinfection)
Physical method
Physical method of sterilization include:
A. Heat
B. Filtration
C. Radiation
Heat
 The most common method used for the elimination of
microorganisms, sterilization by heat
 Sterilization by heat are two types:o Dry heat
o Moist heat
Dry heat
 Dry heat kills by microbes by oxidation, applied mainly
in two ways:1- Direct incineration / red heat / flaming
2- Hot air oven: All the glassware (except those with rubber
linings) are sterilized in oven at 180°C for 20 minutes or
I60 for 90 minutes
Flaming sterilization
Red heat sterilization
Moist heat
 Are more effective than dry heat.
 kills the organisms by denaturing enzymes and structural
proteins of microorganisms
 Moist heat is applied in following ways:
1- Heating below 100ºC:
Pasteurization, have two types:
 Hold method 62.5ºC for 30 minutes
 Flash method 72ºC for 15 seconds
Moist heat
2- Boiling at 100◦C does not ensure sterility.
o Boiling at 100◦C for 10 minutes is usually enough to achieve
sterility for organisms are not present in high concentrations;
in fact most bacteria are killed at about 70◦C.
3- Temperature above l00◦C, using instrument name as
Autoclave, using heat under pressure, it is the most reliable
method
Pasteurization
Boiling
Autoclave
B. Filtration
 Filtration is the passage of a liquid or gas through a filter
with pores small enough to remain microbes.
 Microbes can be removed from air by high -efficiency
particulate air filters.
 High efficiency particulate air (HEPA) filters create clean
atmospheres in areas such as operating theatres and
laboratory laminar-flow hoods.
 For fluids filtration use for products that are damaged by
heat e.g. serum, toxins, antibiotics& vitamins
Filtration
 Membrane filters composed of nitrocellulose or cellulose
acetate are commonly used to filter out bacteria, viruses,
and even large proteins.
 Size range from 0.22 μm – 0.45 μm for bacteria .
 Sizes can go as low as 0.01 μm to filter viruses and
proteins.
Sterilization by filtration
C. Radiation
 The effects of radiation depend on its wavelength,
intensity and duration, to destroys DNA
 Radiation may be used in two forms—ionizing and
nonionizing.
1- Ionizing radiation (gamma rays, electron beams)
o Is of short wavelength and high energy.
o Has a high degree of penetration
o Is used by the medical field for the sterilization of
disposable supplies such as syringes, catheters, and
gloves
Radiation
2- Nonionizing
o Radiation in the form of ultraviolet rays
o Is of long wavelength and low energy.
o Because of its poor penetrability, the usefulness of
nonionizing radiation is limited; it can be used to disinfect
surfaces.
Radiation
Chemical method
(Disinfection)
 Terms as disinfectants and antiseptics
 Different chemical substances used
inanimate and animate objects
 Only few of them have effect on spores.
 It is less effective than sterilization
for
disinfecting
Antiseptic vs. disinfectant
 Antiseptic – An agent used to inhibit or eliminate
microbes on skin or other living tissue (alcohol, iodine,
chlorhexidine)
 Disinfectant – An agent used to destroy microbes on
inanimate objects (phenols, formaldehyde, chlorine
bleach)
Factors That Influence the Degree
of Killing
The following factors play a significant role in the selection
and implementation of the appropriate method of
disinfection:
 Types of organisms
 Number of organisms
 Concentration of disinfecting agent
 Presence of organic material (e.g., serum, blood)
 Nature of surface to be disinfected
 Contact time
 Temperature
 pH
Types
A. Alcohol groups :o
o
o
o
o
The two most effective alcohols used in hospitals for
disinfection purposes are ethyl alcohol and isopropyl alcohol.
Ethanol or Isopropanol, are sometimes used as a disinfectant,
but more often as an antiseptic
These alcohols are non-corrosive but can be a fire hazard.
They also have limited residual activity due to evaporation,
which results in brief contact times unless the surface is
submerged.
They also have a limited activity in the presence
of
organic
material.
Types
B. 2-5 % Phenolic groups:o
Are Oxidizing agents act by oxidizing the cell membrane
of microorganisms, which results in a loss of structure
and leads to cell lysis and death.
C. Chlorine and Chlorine Compounds
o Chlorine and chlorine compounds are some of the oldest
and most commonly used disinfectants.
o They are usually used in the form of hypochlorite, such as
the liquid sodium hypochlorite (household bleach) and
solid calcium hypochlorite.
o Their killing activity is based on the oxidative effects
Types
D. Aldehydes groups:- e.g. Formaldehyde disinfecting
rooms, stores, furniture, clothing& biosafety cabinet
E. Glutaraldehyde:- rapid killing action and remains active
in the presence of organic matter. is extremely
susceptible to pH changes because it is active only in an
alkaline environment
F. Ethylene oxide:- a gaseous disinfectant is of particular
value in sterilizing heat sensitive materials such as
plastics, rubber articles
G. Quaternary ammonium compounds (quats)
H. Halogens
Common example of home disinfectant
Sources
 Textbook of Diagnostic Microbiology-Fifth editionConnie R. Mahon, MS- Donald C. Lehman, EdD,
MT(ASCP), SM(NRM) - George Manuselis, MA,
MT(ASCP)- Elsevier (2015) (Part I –chapter 4)
This is the last lecture in basic microbiology,
I wish all of you luck and success