below, cultured mycobacteria and potentially contaminated samples should be handled or processed in a biological safety cabinet
(BSC) following the containment recommendations of the CDC
Biosafety in Microbiological and Biomedical Laboratories
(BMBL) [7].
1.11 Occupational
Exposure
to M. tuberculosis
Laboratory exposures from M. tuberculosis are known hazards for
laboratorians as well as workers in autopsy suites and healthcare
facilities who may be exposed to infection via aerosols.
M. tuberculosis infection is three times higher for laboratory staff
working with M. tuberculosis than for those not working with
it. Infected nonhuman primates also pose a risk for infection to
laboratory staff [7]. Rodents do not produce droplets via coughing
and so do not pose the same level of risk to human workers, but
material from cages can become aerosolized and pose a risk for
infection to staff. The risk of infection is greatly increased in immunocompromised individuals.
Tuberculosis bacteria have been found in sputum, cerebrospinal fluid, urine, and tissues. Aerosols generated when handling
samples in the laboratory pose the greatest hazard. BSL-2 precautions and facilities should be used when handling specimens for
staining or producing tissue sections. Aerosol-generating procedures should be minimized or eliminated. For example, slides
should be methanol-fixed (see Subheading 3.1) or heated on a
slide warmer, although heat-fixed samples can still be infectious.
Heat-fixing by flame should be avoided. Handling of sputum for
staining can be done on an open bench after being treated with an
equal volume of 5% hypochlorite solution (undiluted household
bleach) and incubating at room temperature for 15 min before
handling outside a BSC [20].
Any growth of the organism or procedures that may generate
aerosols should be performed in a BSL-3 facility with BSL-3 safety
protections in place, including a respiratory protection plan and
BSCs. The ID 50 of M. tuberculosis is <10 bacteria [20].
Mycobacteria are capable of remaining viable on hard surfaces
for weeks or months when protected from sunlight. Some species,
including the M. tuberculosis complex, can survive on surfaces, in
soil, or animal waste for months and remain potentially infectious.
Mycobacteria are susceptible to UV light and heat (>65
C for at
least 30 min) but are resistant to freezing or desiccation. For
nonspore-forming bacteria, they are remarkably resistant to acids
and alkalines as well as some chemical disinfectants [19].
For large-scale cleaning, mycobacteria are sensitive to ethylene
oxide, formaldehyde vapor, chlorine compounds, 70% ethanol, 2%
alkaline glutaraldehyde, peracetic acid, phenol-based disinfectants,
and stabilized hydrogen peroxide. Caution should be taken when
selecting a disinfectant that contains an organic material. Agents
that have reduced efficacy when used with organic matter,
Culturing Mycobacteria
11
(BSC) following the containment recommendations of the CDC
Biosafety in Microbiological and Biomedical Laboratories
(BMBL) [7].
1.11 Occupational
Exposure
to M. tuberculosis
Laboratory exposures from M. tuberculosis are known hazards for
laboratorians as well as workers in autopsy suites and healthcare
facilities who may be exposed to infection via aerosols.
M. tuberculosis infection is three times higher for laboratory staff
working with M. tuberculosis than for those not working with
it. Infected nonhuman primates also pose a risk for infection to
laboratory staff [7]. Rodents do not produce droplets via coughing
and so do not pose the same level of risk to human workers, but
material from cages can become aerosolized and pose a risk for
infection to staff. The risk of infection is greatly increased in immunocompromised individuals.
Tuberculosis bacteria have been found in sputum, cerebrospinal fluid, urine, and tissues. Aerosols generated when handling
samples in the laboratory pose the greatest hazard. BSL-2 precautions and facilities should be used when handling specimens for
staining or producing tissue sections. Aerosol-generating procedures should be minimized or eliminated. For example, slides
should be methanol-fixed (see Subheading 3.1) or heated on a
slide warmer, although heat-fixed samples can still be infectious.
Heat-fixing by flame should be avoided. Handling of sputum for
staining can be done on an open bench after being treated with an
equal volume of 5% hypochlorite solution (undiluted household
bleach) and incubating at room temperature for 15 min before
handling outside a BSC [20].
Any growth of the organism or procedures that may generate
aerosols should be performed in a BSL-3 facility with BSL-3 safety
protections in place, including a respiratory protection plan and
BSCs. The ID 50 of M. tuberculosis is <10 bacteria [20].
Mycobacteria are capable of remaining viable on hard surfaces
for weeks or months when protected from sunlight. Some species,
including the M. tuberculosis complex, can survive on surfaces, in
soil, or animal waste for months and remain potentially infectious.
Mycobacteria are susceptible to UV light and heat (>65
C for at
least 30 min) but are resistant to freezing or desiccation. For
nonspore-forming bacteria, they are remarkably resistant to acids
and alkalines as well as some chemical disinfectants [19].
For large-scale cleaning, mycobacteria are sensitive to ethylene
oxide, formaldehyde vapor, chlorine compounds, 70% ethanol, 2%
alkaline glutaraldehyde, peracetic acid, phenol-based disinfectants,
and stabilized hydrogen peroxide. Caution should be taken when
selecting a disinfectant that contains an organic material. Agents
that have reduced efficacy when used with organic matter,
Culturing Mycobacteria
11