Antimicrobial Effects of Household Substances on Escherichia coli

Overview

This study evaluated the antimicrobial activity of honey, lemon juice, vinegar, and saltwater against Escherichia coli grown on agar plates. Chlorine and water were used as positive and negative controls. Filter paper disks soaked in each solution were placed on inoculated plates and incubated at 37°C. Zones of inhibition were measured in centimeters across multiple trials to quantify bacterial growth suppression. To standardize results, antimicrobial effectiveness was calculated as a percentage relative to chlorine using the formula: (zone of inhibition of substance ÷ zone of inhibition of chlorine) × 100. This allowed direct comparison of each substance to the positive control. Lemon juice produced a larger average zone of inhibition (0.65 cm) than vinegar (0.405 cm), while saltwater and honey showed smaller effects. Chlorine demonstrated the greatest inhibition, and water showed none. When normalized to chlorine, all tested substances showed reduced effectiveness, confirming chlorine as the most potent antimicrobial. The hypothesis that lemon juice would be more effective than vinegar was supported, likely due to its lower pH disrupting bacterial cell function. These results suggest that acidity plays a key role in antimicrobial activity, although none of the tested substances matched the effectiveness of chlorine.

Competition history

• CSEF 2026 Microbiology (Senior Division) · Entry S-16-06

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