MLAB 2434 – CLINICAL MICROBIOLOGY
SUMMER, 2005
CECILE SANDERS & KERI BROPHY
Chapter 2 – Control of
Microorganisms
Chapter 2 – Control of
Microorganisms (cont’d)

Sterilization vs. Disinfectant

Sterilization
• Removes all forms of life, including
spores
• “All or nothing” process
• Chemical or physical
Chapter 2 – Control of
Microorganisms (cont’d)

Disinfection
• Removes all pathogenic organisms but
not necessarily all spores
• “Disinfectants” are chemicals applied to
inanimate objects
• “Antiseptics” are disinfectants applied
to living tissue
Chapter 2 – Control of
Microorganisms (cont’d)

Factors Influencing Degree of
Killing
Types of organisms - Bacterial
spores, mycobacteria, nonlipid
viruses, fungi, bacteria, lipid viruses
(most resistant to least resistant)
 Number of organism – microbial load
 Concentration of disinfecting agent

Chapter 2 – Control of
Microorganisms (cont’d)
Organic soil present
 Nature of surface to be disinfected


Methods of Disinfection &
Sterilization

Physical Methods
• Heat – autoclave = 15 psi at 121° C for
15 minutes (Boiling and pasteurization
disinfect but do not sterilize)
Chapter 2 – Control of
Microorganisms (cont’d)
• Filtration
• Radiation

Chemical Methods
• Alcohols – ethyl and isopropyl at 6090% concentration
• Aldehydes (formaldehyde,
glutaraldehyde)
• Halogens
• Iodine (Tincture and Iodophore)
• Chlorine and chlorine compounds
Chapter 2 – Control of
Microorganisms (cont’d)
• Heavy metals – rarely used; example =
silver nitrate in newborns’ eyes
• Detergents – surfactants; limited to
non-critical areas like bench tops and
floors
• Phenolics – disinfection of hospital
environments
• Gases – ethylene oxide
Chapter 2 – Control of
Microorganisms (cont’d)

Microbiology Laboratory Safety
Program
Address biological hazards
 Describe safe handling, storage and
disposal
 Procedures in event of fire, natural
disasters, and bomb threats
 Correct techniques for lifting and
moving heavy objects

Chapter 2 – Control of
Microorganisms (cont’d)

Handling Biological Hazards

Two sources of hazards:
• Patient specimens
• Actively growing cultures of
microorganisms
Chapter 2 – Control of
Microorganisms (cont’d)

“Levels of Protection”
• Level 0 = handling materials and
performing tasks that do not involve
contact with or exposure to blood, body
fluids, body secretions, or tissues (e.g.,
reading routine culture plates at
bench); requires buttoned lab coat
• Level 1 = specimen receiving; requires
gloves and buttoned lab coat
Chapter 2 – Control of
Microorganisms (cont’d)
• Level 2 = processing and planting
specimens for culture and direct
examination on slides or performing any
activity that can generate aerosols;
requires gloves, buttoned lab coat, and
Class II safety cabinet (or mask and
eye cover if cabinet is not available)
Chapter 2 – Control of
Microorganisms (cont’d)

Safety Cabinets (Hoods) – see page 39 in
text)


Class I – exhaust fan moves the air inward
through the open front. Air uncirculated
and passes through HEPA filter. Example
= chemical fume hood
Class II – air pulled inward and downward
and then passes through HEPA filter
before reaching work surface. Example =
most common microbiology laboratory
hood
Chapter 2 – Control of
Microorganisms (cont’d)

Class III
Self-contained, ventilated system
for highly infectious microorganisms
 Provides highest level of personal
protection
 Closed front contains attached
gloves for work on bench
