The effect of temperature on bactericidal properties of 10% povidone-iodine solution

Ten percent povidone-iodine (PVI) is commonly used as a bactericidal solution before amniocentesis is performed. Warming PVI may increase patient comfort; however, the effect of warming on its bactericidal properties is not known. The objective of this study was to determine the effect of warming 10% PVI on its bactericidal properties.

Room temperature of PVI was 25 degrees C, and temperature in an ultrasonic gel warmer was 32 degrees C. In vitro experiments were conducted in 25 degrees C and 32 degrees C water baths. Nine milliliters of PVI at each temperature was added to 1 mL of bacteria (10(7) organisms/mL Staphylococcus aureus, Enterococcus species, Escherichia coli, group B Streptococcus). After 0.25, 0.5, 1, 2, 4, and 8 minutes, 1-mL samples were removed and added to 4 mL of 0.5% sodium thiosulfate (to neutralize the iodine and interrupt bactericidal action). The number of viable organisms was determined by plating 0.1-mL samples on trypticase soy agar plates. Plates were incubated at 37 degrees C for 24 hours and colony-forming units (CFUs) were counted. For in vivo experiments in 40 volunteers, a 9-cm2 area of the dorsum of each hand was wiped with a sterile cotton swab to obtain a sample of bacteria for culture. The area was then wiped for 15 seconds with PVI at 25 degrees C or 32 degrees C and recultured. The bactericidal properties of PVI at each temperature were compared. The Mann-Whitney U test was used as appropriate, and P <.05 was considered significant.

In vitro, PVI was bactericidal against E coli, S aureus, Enterococcus species, and group B Streptococcus within 0.25 minutes at both 25 degrees C and 32 degrees C, with median bacterial growth of 0 CFU/plate for each species of bacteria studied (3 replicates at each temperature). Median bacterial growth from skin was 4 CFU/plate (range, 0 to >100). After hands were wiped with PVI at 25 degrees C and 32 degrees C, median bacterial growth was 0 CFU/plate (range, 0-8) and 0 CFU/plate (range, 0-15), respectively (not significant).

PVI is as effective at 32 degrees C as it is at 25 degrees C. Use of PVI at 32 degrees C should be considered to increase patient comfort in procedures performed without the use of anesthetics.