Differences in detected fluorescence among several bacterial species measured with a direct-reading particle sizer and fluorescence detector

Naturally-contained fluorescing chemicals (such as riboflavin or NADPH) can be used to detect the presence of biological organisms. A new instrument f rom TSI Incorporated measures fluorescence of particles using an ultraviole t laser operating at an excitation wavelength of 355 nm. We have employed t his instrument (Model 3312 Ultraviolet Aerodynamic Particle Sizer (tm) Spec trometer) to assess the degree of fluoresence associated with a variety of biological aerosols. Nonfluorescent and fluorescent latex sphere and sodium chloride aerosols were first used to assure proper operation of the instru ment and to obtain correct instrument settings. Biological aerosols were th en generated by combining organisms with double distilled and filtered wate r in a Collison nebulizer operated at low pressure. After passage through a charge neutralizer and dilution with humidified air (45% RH), the aerosol was measured downstream for both particle size and fluorescence distributio ns. Bacterial aerosols generated include Bacillus subtilis subsp. niger (sp ores and vegetative cells), Staphylococcus epidermidis, Escherichia coli, a nd Mycobacterium abscessus (a surrogate for M. tuberculosis). Cladosporium spp. fungal spores were also evaluated, and the effect of heat treatment on fluorescence was tested using B, subtilis spores. For each test the percen tage of organisms that produced a fluorescence signal above a threshold was recorded. The organisms demonstrated considerable differences in percent f luorescence, ranging from means of 11% for S. epidermidis to 44% for B. sub tilis spores. Vegetative cells of B. subtilis were generally less fluoresce nt (mean of 33%) than the spores, while the highest level of fluorescence w as associated with heat-treated spores (averaging about 75%). This instrume nt has some potential for use in settings where immediate detection of biol ogical organisms is important. Work remains to be done on understanding the effect on fluorescence of organism viability, presence of nonbiological pa rticles, and interferences from mixtures.