β-N-Acetylhexosaminidase (NAHA) as a Marker of Fungal Cell Biomass – Storage Stability and Relation to β-Glucan

Background. Laboratory and field studies have demonstrated that the enzyme β-N-acetylhexosaminidase (NAHA) is a marker of fungal biomass. The purposes of this study was to determine, 1) the stability of the NAHA enzyme on stored filters, 2) the effect of air movement during the sampling of particles and resulting NAHA enzyme activity, and 3) the relationship between enzyme activity and β-glucan concentration. Methods. Replicate air, filtered (0.8 µm pore, cellulose acetate) samples were obtained and stored at room temperature. Then 7 to 12 samples were analysed at 0, 10, 20, 30 or 360 days. Air samples were collected in rooms with no activity, walking or with fan use. The NAHA activity on the filters was measured by adding an enzyme activator and the fluorescence was measured. The β-glucan concentrations were measured using a Limulus-based test with and without solubilisation with NaOH. Results. Storage of filters up to 360 days did not influence the content of NAHA. Movements in the room increased the NAHA values but agitation in terms of fan blowing did not increase the potential to detect differences between rooms with or without fungal growth. There was a relation between NAHA and the non-soluble fraction of β-glucan. Comments: Enzyme measurements of fungal biomass are rapid and easy to perform. The sensitivity and specificity of the method is high which makes it suitable for field use. Incorporation of the small fungal fractions in exposure assessment is important from a health point of view as they have a higher penetration rate into the deep parts of the lung. Summary: The evaluation of the enzyme method to determine fungal growth further supports the relevance of this method to relate to medical effects of fungal exposure.