Airborne fungi, a significant constituent of atmospheric bioaerosol, are well-known source of allergens and can cause allergic rhinitis and bronchial asthma in sensitive subjects. Rhizopus stolonifer, the filamentous fungus is a widely distributed thread-like Mucoralean mold. Commonly found on bread surfaces, it takes food and nutrients from the bread and causes damage to the surface where it lives. Although a significant exposure risk is assumable in indoor environment, the role of this fungus in provoking allergic symptoms in pre-sensitized individuals, however, was poorly investigated. We conducted this study to monitor airborne R. stolonifer and to evaluate its potential as an aeroallergen causing nasobronchial allergy in sensitized individuals.
Methods: Seasonal periodicity of R. stolonifer was studied for two years (March, 2009-Feb.,11) by Andersen air sampler. The relationships between meteorological parameters and airborne R. stolonifer concentration were explored by linear regression models. The allergic potential of R. stolonifer extract was studied on 389 respiratory allergic patients by performing skin prick tests (SPT) and measuring the allergen-specific IgE levels in SPT positive patient’s sera by Enzyme-linked Immunosorbent Assay. SDS-PAGE and immunoblotting with pooled patient sera were performed to identify its IgE-binding components.
Results:
Airborne R. stolonifer concentration range was 4-47 CFU/m3 and reached the peak concentration in March. Relative humidity was found to be a significant predictor for occurrence of R. stolonifer in air. Positive skin reaction was observed in 105 patients (27%) including 10 (9.5%) showing markedly high (2+ to 3+) skin sensitization. Crude antigenic extract of R. stolonifer was resolved in 16 protein bands in the molecular weight range of 12 to 72 kDa on SDS-PAGE (12% gel). Three IgE-binding protein bands (17, 21and 67.12 kDa) were detected by immunoblot analysis.
Conclusions:
Exposures to R. stolonifer in environments where it naturally occurs may confer risk of IgE-mediated sensitization in sensitive individuals.