Laboratory Practices

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Disinfection

Disinfection is the process of killing pathogens agents by chemical or physical means directly applied. Disinfection does not mean the destruction or removal of all organisms. Therefore, this may not necessarily create sterile conditions.

Work surfaces and equipment must be decontaminated immediately after using biohazardous materials. It is critical that the work area within biological safety cabinets always be cleaned and disinfected thoroughly, using a chemical disinfectant after each use.

Chemical Disinfectants

Chemical disinfectants are effective alternatives since steam sterilization is not feasible for use in large spaces, surfaces, and stationary equipment, high temperatures and moisture also may damage delicate instruments. There are many trade names for the wide variety of disinfectants. Basically, the chemical disinfectants fall into the following categories: acids/alkalis; alcohols; chlorides; formaldehyde; glutaraldehyde; iodine; mercurical; phenolics, and quaternaries.

The relative resistance to chemical disinfectants can be substantially altered by such factors as:

1. Contact time
2. Human error
3. Concentration
4. Presence of organic matter and dirt
5. Temperature
6. Humidity
7. Types and numbers of microorganisms
8. Condition and nature of the surfaces.

The degree of success achieved with chemical decontaminants may range from minimal inactivation of the target microorganism to sterility, depending upon how these factors are manipulated.

Selecting Chemical Decontaminants

No single chemical disinfectant or method will be effective or practical for all decontamination situations. Therefore, consider when selecting chemical disinfectants and procedures, the purpose for decontamination and the interacting factors must be considered.

The following questions will to help in choosing which chemical disinfectant is best:

1. What is the target microorganism?
2. What disinfectants are known to inactivate the target microorganism(s)?
3. What degree of inactivation is required?
4. How is the microorganism suspended (i.e. simple or complex, on solid or porous surfaces, airborne)?
5. What is the highest concentration of cells anticipated to be encountered?
6. Can the disinfectant be expected to contact the microorganisms and can effective contact duration be maintained?
7. Is it compatible with the material to be contaminated?
8. What is the product stability?
9. Will there be an absence of residues?
10. Is the disinfectant nontoxic, non-allergenic, non-carcinogenic, non-irritating, and have no noxious odors?

Agar, proteinaceous nutrients, and cellular materials can be very effective in physically retarding or chemically binding active moieties of chemical disinfectants. These interferences will dictate the use of disinfectant concentrations and contact items in excess of those shown to be effective in the tube test.

Shelf Life

After selection of a chemical disinfectant that is effective against the microbes or agent being investigated, the PI or supervisor will need to schedule regular procurement of bulk concentrate and maintenance of a working disinfectant supply in the laboratory. One way to assure a continuous supply is to maintain two sources of disinfecting solution, i.e., one for immediate use and the other reserved for emergency use (see biosafety spill kit/station). As the immediate-use supply is depleted, the emergency-use lot replaces it and a freshly prepared solution becomes the emergency-use supply. In small laboratories, effective shelf life of a disinfectant may be exceeded before the working supply is exhausted through normal activities. Supervisors must devise schedules for disposal of ineffective residual disinfectants to be replaced with fresh solutions. Economics must not take precedence over assuring adequate quantities of disinfectants are available to cope with concentrated infectious microbes/agents spilled in the laboratory.

Disinfectant Chart:

Disinfectant Class	-cidal Activity Indicated
	Bacteri-	Tuberculo-	Pseudomona-	Spori-	Viru-
Quaternary Ammon. Cpds.	Good	None	Fair	None	Moderate
Phenolic Compounds	Good	Good	Good	Poor	Moderate
Iodine	Good	Good	Good	Moderate	Good
Chlorine Compounds	Good	Good	Good	Moderate	Good
Glutaraldehyde	Good	Good	Good	Good	Good
Formaldehyde	Good	Good	Good	Good	Good
Alcohols	Good	Good	Good	Good	Moderate
Acids/alkalies	Good	Good	Good	Good	Good
Mercurials	Fair	None	Fair	None	Fair

Clicking on a Disinfectant Class will open a window showing the Advantages and Disadvantages of using that paritcular class of disinfectant.