Detection and characterization of airborne Mycobacterium tuberculosis H37Ra particles, a surrogate for airborne pathogenic M-tuberculosis

There is currently no direct sampling and analytical method available for m onitoring airborne environmental Mycobacterium tuberculosis (M. tuberculosi s) expelled from the human respiratory tract. Traditional sampling and anal ytical methods fail to detect airborne environmental M. tuberculosis. To ci rcumvent the need for traditional microbial culturing in order to detect an d identify environmental M. tuberculosis, a commercial DNA diagnostic metho d involving the polymerase chain reaction (PCR) coupled with an enzymatical ly-generated color reaction was interfaced with air sampling methods. Using a laboratory-conditioned avirulent mycobacteria strain, M. tuberculosis H3 7Ra, as a surrogate for pathogenic M. tuberculosis, a single copy of purifi ed M. tuberculosis H37Ra DNA could be detected. A small number of lysed myc obacteria particles, < 10 particles, could also be detected. To develop a s ampling method for airborne ill tuberculosis, liquid suspensions of M. tube rculosis H37Ra were aerosolized in a bioaerosol chamber 3.7 m long with a s quare cross-sectional area of 0.61 m. Samples were collected for PCR analys es using polytetrafluoroethylene filters. Two types of samplers were employ ed, a plastic, disposable filter cassette and an eight-stage cascade impact or called a micro-orifice uniform deposit impactor (MOUDI(TM)). An Andersen six-stage (viable) particle sizing sampler was employed as a reference sam pler since laboratory-conditioned aerosolized M. tuberculosis strains can b e cultured. Although the ill. tuberculosis H37Ra rod-shaped particles had a mean length of 6.6 mu m, the airborne particles were predominantly collect ed on the Andersen 4-6 stages representing an aerodynamic diameter 50% cut point range of 0.6-2.1 mu m and on the MOUDI(TM) 4-7 stages representing an aerodynamic diameter 50% cut point range of 0.3 to 1.8 mu m. The PCR analy ses could be completed in 1-1.5 days, in contrast to the traditional cultur ing methods which required a minimum of 3-5 weeks. This approach could be u sed to study the expulsion of infectious particles from patients and may pe rmit risk-assessment studies in regard to personal respiratory protection a nd the evaluation of environmental controls.