Biological hazards and Laboratory work with Mycobacterium tuberculosis

It must also be emphasized that M. tuberculosis can survive for several days on inanimate surfaces. Survival of M. tuberculosis outside the host can be particularly long with, for example: 90 to 120 days on dust, 45 days on manure, 105 days on paper, 6 to 8 months in sputum (cool, dark location) and 45 days on clothing. Hence a work surface, that has not been properly disinfected, represents an additional source of moderate risk of transmission (Rubin, 1991).
Among the laboratory techniques used for the identification and characterization of mycobacteria, the following practices are likely to increase the risk of contamination or to generate infectious aerosols producing droplet nuclei (Jensen et al., 2005):
1) Handling of containers with clinical specimens: even if this situation is unlikely to generate aerosols, it is the initial step where laboratory personnel is potentially exposed to the tubercle bacilli. It was shown that the outside of containers used for collecting clinical specimens is frequently contaminated by M. tuberculosis (6.5%) or by other airborne pathogens (15%).
2) Centrifugations: fluid may spill from centrifuge tubes or tubes may break, releasing a large amount of aerosols.
3) Pipetting: pipettes and Pasteur pipettes in particular are likely to generate bubbles which burst and form aerosols.
4) Mechanical homogenizing (vortexing, grinding, blending).
5) Sonication, heating or boiling of samples (for instance for the extraction of nucleic acids).
6) Work with bacteriological loops: when loops charged with infectious material are placed in an ordinary bunsen burner, the material may be dispersed before it is burned and contaminate surfaces or the operator.
7) Preparation and manipulation of frozen sections (histology) when frozen material is cut, infected ice and tissue particles may be dispersed and contaminate the operator and material (even formalin-fixed tissues may still contain viable bacilli).
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