Safety in the Microbiology Laboratory

Question 1

Discuss the CDC classification of infectious agents.

Answer 1

Biosafety Level 1 (BSL-1): Agents with no known potential for infecting healthy people
Biosafety Level 2 (BSL-2): Agents that are most commonly encountered in clinical specimens
Biosafety Level 3 (BSL-3): Agents with potential for aerosol transmission; disease may have serious or lethal consequences. Ex. Cultures growing Mycobacteria tuberculosis, mold stages of systemic fungi
Biosafety (BSL-4): Agents that pose high risk of life-threatening disease. Ex: Ebola virus, smallpox virus

Question 2

What is the biosafety level of most hospital clinical microbiology laboratories?

Answer 2

BSL-2 or 3

Question 3

What is the biosafety level of Bacillus anthracis and Yersinia pestis?

Answer 3

BSL-2

Question 4

Name several biosafety level 3 pathogens.

Answer 4

Mycobacterium tuberculosis, Franciscella, Brucella, Rickettsia rickettsii, Coxiella burnetti, and the mold stages of systemic fungi.

Question 5

What are the 4 levels within the laboratory Response Network (LRN) for Bioterrorism?

Answer 5

Level A: Clinical laboratories - Adequate safety to rule-out and forward organisms to a higher level lab
Level B: State Public Health laboratories - Safety and proficiency to confirm and perform susceptibility testing
Level C: State Public Health laboratories and CDC laboratories - Safety and proficiency to probe, type, and perform toxigenicity testing
Level D: CDC and the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) - Safety and proficiency to probe for all bio- and chemical agents; secure banking of isolates; BSL-4

The distinction between Level B and Level C is beginning to blur and reclassification is likely.

Question 6

Describe the 3 classes of biological safety cabinets (BSC).

Answer 6

Class I: Room air passes into the cabinet. Only the air being exhausted is sterilized.
Class II: Air flowing into and out of the cabinet is sterilized.
Class III: Completely enclosed; work is done with rubber gloves that are attached and sealed to the cabinet. Air coming in and going out is sterilized. Used in BSL-4 facilities.

Question 7

Which class of biological safety cabinet is appropriated for most clinical work?

Answer 7

Class II

Question 8

How is air sterilized in a biological safety cabinet?

Answer 8

Most commonly by HEPA filters. UV light or heat are also used.

Question 9

How often must the biological safety cabinet be inspected?

Answer 9

Annually

Question 10

What work should be conducted in a biological safety cabinet?

Answer 10

Any manipulation of clinical specimens, for example, plating and direct smear preparation, and all mycobacteriology and mycology. In most cases, patient specimens pose a greater risk to laboratory workers than bacteria in culture, so most plate-reading and follow-up testing is performed outside of the BSC. The exception is BSL-3 pathogens, which should always be handled in a BSC.

Question 11

When should masks be worn in the microbiology lab?

Answer 11

Whenever there is a risk of aerosol formation during specimen handling and when working with AFB, fungal, and other BSL-3 cultures.

Question 12

What are the 5 infections that have been most frequently acquired in the clinical microbiology laboratory?

Answer 12

Shigellosis, salmonellosis, tuberculosis, brucellosis, and hepatitis.

Question 13

What is the difference between a bacteriostatic and bacteriocidal agent?

Answer 13

A bacteriostatic agent inhibits the growth of bacteria; a bacteriocidal agent kills bacteria.

Question 14

How do disinfectants and antiseptics differ?

Answer 14

Antiseptics are sued on living tissues to prevent or arrest the growth of microorganisms. Disinfectants are used on inanimate objects to kill microorganisms. Disinfectants vary in their effectiveness in killing spore-forming bacteria and Mycobacteria.

Question 15

What is the phenol coefficient?

Answer 15

A value which compares the killing power of a disinfectant to that of phenol.

Question 16

What is the most practical and dependable method of sterilization?

Answer 16

Steam under pressure (autoclave).

Question 17

What are the pressure, time, and temperature routinely used for autoclaving?

Answer 17

15 pounds of pressure, 15 minutes, 121C.

Question 18

How can one ensure that the autoclave is reaching the correct temperature?

Answer 18

Various commercial systems are available. Most of these use Bacillus stearothermophilus, a spore producer. Following autoclaving and incubation, there should be no growth of the organisms. Autoclaves should b tested weekly.

Question 19

Which type of bacteria are most difficult to eliminate from the environment?

Answer 19

Bacteria that produce spores.

Question 20

Is boiling an effective method of sterilization?

Answer 20

No, because spores can survive.

Question 21

Name a gas used for sterilization.

Answer 21

Ethylene oxide. IT is used to sterilize hospital equipment that cant withstand steam.

Question 22

Explain how to package a biological agent for shipping.

Answer 22

The specimen is placed in a watertight primary container. The primary container is placed in a secondary container with enough absorbent material to absorb the contents in the event of breakage. The secondary container is placed in a mailing container labeled with an etiologic agent label, biohazard symbol, and phone number of the Centers for Disease Control and Prevention.