Abstract

Nigerian currency notes come in paper and synthetic polymer denominations. The present study investigated used paper notes in the Naira (₦) denominations of ₦100, ₦200, ₦500 and ₦1000 notes for bacterial load and quality using standard microbiological methods. This investigation was carried out to address inaccurate methodologies in works on microbial contamination of Nigerian currencies, which do not take into account the total surface area of study notes. Each note was immersed in 150 ml physiological saline for 20 minutes with shaking at intervals to dislodge cells into suspension. This was followed by 10-fold serial dilutions and plating on nutrient agar and MacConkey agar. Colonies that developed on the plates were counted and populations were accurately calculated in CFU/cm² using a mathematical formula developed in this study. Identification of isolates was carried out based on cultural characteristics, cell morphology, Gram reactions, and biochemical tests. Results showed that populations were highest on ₦100 notes (4.6  1.2 x 10⁵ CFU/cm²) and least on ₦1000 notes (0.4  0.2 x 10⁵ CFU/cm²). Isolates were identified as Staphylococcus aureus, Bacillus sp., E. coli, Micrococcus sp., and Pseudomonas aeruginosa. Distribution of these species showed that Bacillus sp. was the most prevalent whereas Pseudomonas aeruginosa was the least. It was concluded that fairly used Nigerian currency notes harbour a variety of bacterial species whose populations in CFU/cm² can be determined using a general mathematical formula. Since these organisms are known pathogens, particularly to immunocompromised individuals, it becomes important to treat currency notes with utmost care so that they do not constitute fomites for transmission of diseases.