Mycological investigation on bat droppings of Tadarida brasiliensis from Austin, Texas

 

    Indoor air quality management suggests that any bat droppings present indoor or near the residence or office environment is of major health concern and a potential source of health hazard. This is because of the suspicion of the presence of fungal

material and their growth in bat droppings. The molds that grow in moist, warm, highly organic situations found in bat droppings are known to increase asthma attacks in affected people. To find out the presence of fungi in bat droppings, a study was conducted on the droppings of bat species Tadarida brasiliensis (Mexican Free-tailed Bat) belonging to Suborder Microchiroptera of the order Chiroptera. The droppings were collected from "The world's biggest urban bat roosting colony" i.e. Congress Avenue Bridge of Austin, Texas. Dilution plate technique was conducted to isolate the fungi present in the droppings. Further, direct microscopy was employed to study the presence of fungal spore types, pollen grains and other materials present.

 

    Altogether 9 species belonging to 5 genera of fungi were recorded from the droppings of T. brasiliensis apart from yeast colonies and non-sporulating colonies. The bat droppings of T. brasiliensis yielded 172.11 X 10³ colonies/gm on an average. The colonies belonging to yeasts dominated the droppings and contributed around 40.8% followed by Cladosporium sphaerospermum (25.56%), C. cladosporioides (23.33%) and C. chlorocephalum (8.8%) in the order of dominance. The direct microscopic observation yielded only 4 spore types apart from the hyphal fragments. The average number of 1.78 x 106 fungal spores and 12.3 x103 pollen grain were recorded. The number of insect scales exceeded 216,500/gm on an average. Recording insect scale in large number revealed the feeding behavior of the mammal. It is concluded that the presence of yeast colonies in large numbers may emerge as a pathogen of the exposed human subject and immunocompromised individuals. The dry, airborne insect scales may also function as an irritant to the respiratory system of the exposed subjects.