Abundance of airborne Penicillium CFU in relation to urbanization in Mexico City

Air was sampled simultaneously at three localities in Mexico City differing in urbanization index and air pollution level on 22 days during a period covering both dry and rainy seasons. An Andersen two-stage microbial sampler was used for 15 min at 28 liters min-1 to isolate culturable fungi on malt extract agar. After exposure, plates were incubated at 25 degrees C for 48 to 72 h before colonies were counted and identified to give concentrations of total fungal spores and of Penicillium spp., expressed as CFU per cubic meter of air. Total fungi numbered 91 to 602 CFU m-3 in Tlalpan Borough (southern area), 40 to 264 CFU m-3 in Cuauhtemoc Borough (downtown), and 26 to 495 CFU m-3 in Gustavo A. Madero Borough (northern area). Although Penicillium spp. were the second most frequently isolated fungal genus, concentrations were small, with a maximum of only 133 CFU m-3. Twice as many colonies were isolated in the southern area, with an urbanization index of 0.25 (arithmetic mean, 41 CFU m-3), as at other sampling stations with greater urbanization indices (arithmetic means, 19 and 20 CFU m-3). In the downtown area, with an urbanization index of 1.0, Penicillium spp. were more numerous than any other genus and formed 25% of the total fungal count compared with 14 and 17% in the other areas. Concentrations of airborne Penicillium spp. did not differ significantly between rainy and dry seasons. However, their concentration was weakly negatively correlated with temperature (r = 0.36, P < 0.01), vapor pressure (r = -0.47, P < 0.001), and relative humidity (r = -0.36, P < 0.001). On average, 70% of Penicillium propagules were collected in the small-particle fraction (considered to be respirable on inhalation, < 5 micrometers aerodynamic diameter). Of the eight Penicillium species identified, P. aurantiogriseum, P. crustosum, P. chrysogenum, and P. spinulosum were the most common. Their small numbers suggest that Penicillium spp. are not important outdoor aeroallergens in Mexico City, but total exposure cannot be assessed until indoor environments have been sampled.