Variation in the fluorescence intensity of thermally-exposed bacterial bioaerosols

This study describes the real-time fluorescence characteristics of bacterial bioaerosols (Escherichia coli and Bacillus subtilis) thermally inactivated to produce various degrees of cellular culturability. Bacterial bioaerosols were exposed to various temperatures for very short times in a thermal electric tube furnace and then passed into an aerosol fluorescence measurement system that measured the ultraviolet (UV) light-induced fluorescence intensity of airborne particles in real time. The fluorescence of particles in the optical sensing zone was continuously measured with two photomultiplier tubes (PMTs) equipped with optical filters to detect radiation in the UV and visible (Vis) bands. The results showed that both UV- and Vis-fluorescence intensities decreased with increasing deactivation temperature. Also, the ratio of UV- to Vis-fluorescence decreased with increasing temperature for each bacterial bioaerosol. Under the same experimental conditions, we found that the airborne aromatic amino acids (L-tryptophan and L-tyrosine) and ovalbumin particles showed similar reduction trends in their fluorescence characteristics, compared with the test bacterial bioaerosols. These results provide basic information on the feasibility of intrinsic fluorescence measurements for real-time characterization of biological particles.