MLAB 2434 –MICROBIOLOGY
KERI BROPHY-MARTINEZ
Chapter 4 – Control of
Microorganisms
Control of Microorganisms
(cont’d)

Sterilization vs. Disinfectant

Sterilization
• Removes all forms of life, including
spores
• “All or nothing” process
• Chemical or physical
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. They do not kill spores.
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)
Control of Microorganisms
(cont’d)






Number of organisms – microbial load
• The higher the number of organisms,
more exposure to the killing agent is
required.
Concentration of disinfecting agent
Presence of organic material
• Affects killing activity by inactivating
disinfecting agent
Nature of the surface to be disinfected
Contact time
Temperature
Control of Microorganisms
(cont’d)

Methods of Disinfection & Sterilization
 Physical Methods: mainly for sterilization
• Moist Heat – autoclave = 15 psi at 121°
C for 15 minutes
• Dry Heat- 1.5-3 hours @ 160- 180o
• Bacticinerator
• Hot air ovens ( glassware)
• Boiling & pasteurization
• Do NOT sterilize or remove spores
Control of Microorganisms
(cont’d)
• Radiation: used to sterilize disposable
medical supplies (catheters, syringes)
• Filtration
• Liquids: liquid is pulled through cellulose
acetate or cellulose nitrate membrane with
a vacuum. Used for heat sensitive liquids
such as serum, antibiotic solutions, toxic
chemicals and vaccines
• Air: use high-efficiency-particulate air
(HEPA) filters. Designed to remove
organisms larger than 0.3 µm from isolation
rooms, biological cabinets and respirators
Control of Microorganisms

Quality control for Sterilization Procedures


For each load:
• Temperature & duration of cycle
should be checked and recorded
• Indicator tape is attached to each
item
Weekly:
• Check biological indicators
• Bacterial spores are used as
indicator of sterilization
• Sporestrips are placed in the
center of the load to be
sterilized. After the cycle, the
strips are cultured to
demonstrate complete kill.
• Spores used
• Bacillus
stearothermophilusmoist steam
• Bacillus subtilis- dry heat
Control of Microorganisms

Chemical Methods: used in disinfection
Control of Microorganisms
(cont’d)

Microbiology Laboratory Safety Program
 Address biological hazards
 Describe safe handling, storage and disposal of
biological hazards & chemicals
• MSDS: Material Safety Data Sheets


• Biohazard bags & sharps containers
Correct techniques for lifting and moving heavy
objects
Procedures in event of fire, natural disasters, and
bomb threats
• Fires: R= rescue A= alarm C= contain E=extinguish
• Electrical: grounded 3-pronged plugs, check for frayed cords
Control of Microorganisms
(cont’d)

Occupational Safety and Health
Administration (OSHA)
Safety training for potentially
exposed employees
 Goal is to protect workers

Control of Microorganisms
(cont’d)

Exposure Control Plan
 Required by OSHA
• Determine tasks that may result in hazards
• A plan to investigate exposure and prevent
reoccurrences
• Methods of compliance with universal
precautions
• Engineering and work practice controls
• Personal protective equipment (PPE)
• Workplace cleanliness
• Handling and disposal of waste
• Active hazard training programs
Control of Microorganisms
(cont’d)

Universal/standard precautions
 Developed in 1985, redone in 1996
 All blood and body fluids are treated as infectious
• Lone exception is sweat
 Precautions address
• Hand washing
• Gloves, mask, eye protection
• Lab coats
• Appropriate sharps disposal
• Environmental controls
• Employers are required to provide
appropriate PPE
Control of Microorganisms
(cont’d)

Engineering controls

Controls designed to remove
hazards from the workplace
• Some examples are eye wash stations,
safety showers, eye shields
Control of Microorganisms
(cont’d)

Handling Biological Hazards

Two sources of hazards:
• Patient specimens
• Actively growing cultures of
microorganisms
Control of Microorganisms
(cont’d)

Biosafety levels (BSL)

BSL-1
• Well classified and not known to cause
disease
• Standard PPE

BSL-2
• Moderate potential hazard
• PPE and BSC class I
Control of Microorganisms
(cont’d)


BSL-3
• Potential aerosol transmission
• Agents may have serious lethal consequences
• PPE, BSC Class II or III, negative-pressure
rooms
BSL-4
• Dangerous and exotic pathogens
• PPE, BSC Class III, negative-pressure rooms
• Decontamination of room and personnel after
use
Control of Microorganisms
(cont’d)

Safety Cabinets (Hoods)


Class I – exhaust fan moves the air inward
through the open front. Air 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
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

Safety Cabinets (Hoods)
References




Engelkirk, P., & Duben-Engelkirk, J. (2008). Laboratory Diagnosis of
Infectious Diseases: Essentials of Diagnostic Microbiology . Baltimore, MD:
Lippincott Williams and Wilkins.
http://www.diytrade.com/china/4/products/3957592/EO_Gas_Indicator_ta
pe.html
http://www.fishersci.com/ecomm/servlet/fsproductdetail?catalogId=1&productId=664041&langId=1&storeId=10652&distype=2&isChemical=false&fromSearch=0
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic
Microbiology (4th ed.). Maryland Heights, MO: Saunders.