Fungal quality and molecular characterization of aflatoxin-producing Aspergillus species in irrigation water and fresh vegetables in Southwest Nigeria

Abstract

Fungal species were isolated from irrigation water, cultivation soil, and fresh vegetables samples were obtained from a vegetable field in Southwest Nigeria. Aspergillus group, identified by amplification and sequencing of their internal transcribed spacer (ITS) region, were further characterized for aflatoxin production using standard spectrophotometry (365 nm). The highest mean ± SD fungal counts were 3.23 x 103 ± 0.03 CFU/g, 3.07 x 104 ± 0.01 CFU/g and 8.67 x 102 ± 0.13 CFU/ml for vegetable, soil, and water samples, respectively. A total of 32 fungal strains isolated were presumptively identified as Aspergillus sp. (50%), Fusarium sp. (6.25%), Chrysonilia sitophila (3.13%), Acremonium sp. (6.25%), Mucor sp. (12.5%), and Rhizopus sp. (21.87%). The molecular characterization of Aspergillus strains revealed Aspergillus aculeatus, Aspergillus fijiensis, Aspergillus flavus, Aspergillus japonicas, and Aspergillus niger. All the 16 Aspergillus species showed aflatoxin B1 production with Aspergillus japonicus (AWF27) isolated from the irrigation water having the highest concentration (106 µg/kg) and Aspergillus fijiensis (ASF6) isolated from soil having the lowest concentration (93 µg/kg). The work revealed the potential for human exposure to mycotoxin through contaminated fresh vegetables. Concerted effort is required, especially in developing countries for cultivation of fresh vegetables in hygienic environment with clean irrigation water.