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

stearothermophilus- moist 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 employeesGoal 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 controlsControls 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_tape.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.