N.11 – Mycobacterium tuberculosis bioaerosol sampling



Mycobacterium tuberculosis is a very well known old enemy that after some decades of relative “sleeping” is now again a “new emerging” disease. The World Health Organisation (WHO) estimated more than 8 million new cases and 3 million deaths are occurring annually.

The micro-organism is spread by the airborne transmission of droplets produced by infectious individuals while they are sneezing, speaking, laughing, coughing.


Bio-aerosol sampling

The indoor concentration of Mycobacterium tuberculosis is generally quite low and therefore the bioaerosol sampling must be done with care following a detailed sampling protocol to avoid false negative results. The director or responsible of the project must keep in mind that false-negative results are quite possible and should interpret all negative findings with caution. The main reason of sampling is to verify the possible airborne transmission during epidemiological investigations and to evaluate engineering controls.



Microbiology air sampler

Maxi Contact plate diameter 84 mm



(a) Sampling operator should be equipped with appropriate personal protective equipment to prevent inhalation of contaminants (respiratory protection, bio-hazard type clothing, gloves, etc.) and should follow appropriate safety procedures / protocols (disinfection, sterilisation, etc.) when typical tuberculosis diagnosed symptoms were reported.

(b) Sampling operator should clearly know the reason of this specific sampling and understand the limitations of the sampling techniques.

(c) All the sampling procedures should be co-ordinated with the director or responsible of the microbiology laboratory that will perform the subsequent tests.

(d) The sampling of each site should be performed at least in triplicate because the indoor concentration is normally low and, due to the fact the Mycobacterium tuberculosis is a slow growing bacterium, there is the risk that the agar medium is overgrown by fungi with consequent difficult interpretation.

(e) A portable microbiology air sampler should be used to facilitate the collection of several samples and large volumes of air.

(f) The volume of aspirated air by the microbiology air sampler should be 500 / 1000 litres. This volume should be reduced to 200 litres in case a high contamination is expected.

(g) The air samplers should be programmed with the “interval time” automatic mode to have more probability to collect this germ (eg.: 5 samplings every ten minutes).

(h) It is suggested to use Maxi Contact Plate diameter 84 mm (instead of the traditional 55 mm Contact Plate) with the air sampler to have a better distribution of micro-organisms on the agar surface, due to the fact the probable presence of large fungi could mask the M. tuberculosis growing.