Evaluation of fungal contaminants in stored grains and their pathogenic potentials

Abstract

Stored cereal grains such as rice, maize, and millet are highly susceptible to fungal contamination, which compromises food quality and poses significant public health risks. This study evaluated the microbiological quality and pathogenic potential of three commonly consumed grains rice, maize, and millet, retailed in three major markets within the Port Harcourt Metropolis (Mile 1, Mile 3, and Rumuokoro). Specifically, it quantified the fungal load and assessed the biofilm-forming capability of the isolates as an indicator of virulence. Nine grain samples were analyzed, and Total Fungal Plate Counts (TFPC) were determined using standard serial dilution and plating techniques. Biofilm formation was assessed using the Brain Heart Infusion (BHI), Congo Red Agar method. Statistically significant differences were observed in fungal loads across both markets and grain types (p < 0.001). Mean fungal counts ranged from 1.5 × 10⁵ CFU/g in millet from Mile 1 to 3.6 × 10⁵ CFU/g in rice from Rumuokoro, values that exceeded the acceptable safety limit of 1 × 10⁴ CFU/g. The predominant fungal contaminants were Rhizopus spp. and yeasts (26.7% each), followed by Fusarium, Penicillium, and Mucor (10% each), Aspergillus and Cladosporium (6.7% each), and Alternaria (3%). Zygomycetes demonstrated the highest virulence potential, with 50% of Rhizopus and 66.7% of Mucor isolates exhibiting strong biofilm formation. All Alternaria isolates were biofilm-positive. Moderate biofilm production was observed in Fusarium (33.3%) and yeast isolates (25%), whereas Aspergillus, Penicillium, and Cladosporium isolates did not produce biofilms. The high fungal burden, coupled with the presence of biofilm-forming isolates, underscores the need for improved post-harvest handling practices, including rapid drying, adequate storage conditions, strict sanitation, and periodic microbial surveillance. These measures are essential to safeguard grain quality and mitigate potential health risks to consumers.

Keywords: Biofilm, fungal contaminants, food safety, pathogenic, public health, stored grains, total fungal plate count.