Incidence of heat-resistant fungi in Nsukka, southern Nigeria

A total of 42 soil samples collected from different parts of Nsukka, Southern Nigeria, and 20 freshly plucked mango fruits were screened for the presence of heat-resistant fungi. Each soil sample, suspended in sterile water, and washings from each mango fruit were separately heated at 70 degrees C for 1 h before plating on double-strength potato dextrose agar containing chloramphenicol and incubating at approx. 28 degrees C. Approximately 98% of all soil samples and 17% of mango fruits contained heat-resistant fungi which were identified as Neosartorya fischeri, N. fischeri var. spinosa, Aspergillus flavus, Penicillium citrinum and Paecilomyces varioti which has not been reported in tropical soil. Neosartorya spp. were predominant and occurred in all positive samples. Fungal counts ranged from non-detectable to 200 colony-forming units per 10 g of soil. Most isolates appeared to grow faster at 35 degrees C than at 30 degrees C and 40 degrees C.