Increased bactericidal activity of dilute preparations of povidone-iodine solutions

Recent confirmation of intrinsic bacterial contamination of 10% povidone-iodine solution has raised questions regarding the bactericidal mechanism of iodophors and the possibility for survival of vegetative bacterial cells in iodophor solutions. In this laboratory investigation, five different species were exposed to various dilutions of three commercial preparations of 10% povidone-iodine solution; survival was assessed after exposure for time periods varying between 0 and 8 min. All brands of povidone-iodine solution tested demonstrated more rapid killing of Staphylococcus aureus and Mycobacterium chelonei at dilutions of 1:2, 1:4, 1:10, 1:50, and 1:100 than did the stock solutions, S. aureus survived a 2-min exposure to full-strength povidone-iodine solution but did not survive a 15-s exposure to a 1:100 dilution of the iodophor. Both stock and dilute preparations of 10% povidone-iodine solution demonstrated rapid bactericidal action against Klebsiella pneumoniae, Pseudomonas cepacia, and Streptococcus mitis.