Abstract
Objective
The search for an ideal field water disinfectant persists, despite many available products. While other forms of iodine have demonstrated effectiveness, there is a paucity of data available regarding the use of iodophores such as povidone-iodine (PVI) to disinfect water. Escherichia coli is the most common cause of traveler's diarrhea and is found in tropical, temperate, and cold waters. We sought to experimentally determine the minimal disinfecting concentration of 10% PVI over different contact times when added to water inoculated with E coli at varying water temperatures.
Methods
Full-strength 10% PVI was added to sterile deionized water to create 1:100, 1:1000, and 1:10 000 dilutions. E coli were exposed to these strengths of PVI for 5, 15, and 30 minutes. The bactericidal activity of PVI was neutralized with 0.5% sodium thiosulfate. The number of viable colony forming units was determined after 24 hours of incubation at 37°C on Luria-Bertani agar. Effective bactericidal activity was defined as a 5-log reduction (99.999% bacterial kill). This procedure was repeated at 10°C, 20°C, and 30°C.
Results
The lowest concentration of 10% PVI resulting in effective disinfection of water inoculated with E coli was the 1:1000 dilution and was seen after 5 minutes of contact time. The 1:100 concentration of 10% PVI always resulted in effective disinfection, while the 1:10 000 concentration never effectively disinfected the water. No significant differences were observed across the experimental temperatures.
Conclusions
A 10% PVI concentration between 1:1000 to 1:10 000 has been suggested by past authors as a possible but unproven strength for water disinfection. Our experiment supported this suggestion against E coli, the organism most commonly responsible for traveler's diarrhea. This amount of available iodine per liter of treated water is safe, but further studies are needed to assess the effectiveness of PVI against more virulent waterborne pathogens.