Disinfection of Waterborne Coliform Bacteria by Neem Oil

This study assessed the ability of Neem oil to disinfect an Escherichia coli isolate in pure laboratory-grade water and total and fecal coliform bacteria in two unfiltered surface waters. Neem oil doses as low as 2.13 g . L-1 with 5 min of mixing time achieved high levels of inactivation of the E. coli in pure laboratory-grade water (>99% inactivation). However, the disinfection of total and fecal coliforms in the unfiltered surface waters was variable and limited to <70% inactivation typically. Increasing the Neem oil dose and mixing time generally resulted in an increase in the mean inactivation of total coliform bacteria but not always of fecal coliform bacteria. The inactivation of total coliforms was consistently greater than the inactivation of fecal coliforms, suggesting a potential range of sensitivities to Neem oil among coliform bacteria. Reduced effectiveness of the Neem oil in the unfiltered surface waters compared to the pure laboratory-grade water suggests a possible interference by natural water constituents (e.g., suspended particles, dissolved organic matter), which may inhibit the antibacterial potential of Neem oil, or that naturally occurring bacteria are more resistant to the antimicrobial effects of Neem oil. Overall, Neem oil was found to be insufficient on its own for use as a disinfectant of potable water; however, further investigation is recommended into the performance of Neem oil disinfection when combined with pretreatment steps (e.g., sand or cloth filtration) and into methods for concentrating the active antimicrobial ingredients of Neem oil to form more potent disinfectant solutions.