INVITRO AND INVIVO BACTERICIDAL ACTIVITIES OF 10-PERCENT 2.5-PERCENT, AND 1-PERCENT POVIDONE IODINE SOLUTION

The bactericidal action of three formulations of a povidone-iodine (PVI) complex in vitro, in vivo, and in the presence of competing organic matter was evaluated. Bacterial organisms included Staphylococcus aureus ATCC 25923 and 25 clinical isolates of Staph. aureus, designated KU 1-25. For the in vitro studies, 1.0 mL of bacterial inoculum containing 107 organisms was introduced into 9.0 mL of chemically stable 10% and 1% PVI formulations in sterile culture tubes, and 1.0-mL samples were withdrawn at set intervals. Samples were plated by using standard techniques and incubated for 24 hours, after which colony-forming units were counted. For in vivo studies, 0.1 mL of 106 Staph. aureus ATCC 25923 or KU inoculum was deposited on the dorsum of the hand of healthy human subjects. This area was wiped with a cotton swab saturated with 1%, 2.5%, or 10% PVI formulations. Samples were taken at 15 and 30 seconds after application of the iodophor. To test the bactericidal activity of the three formulations in the presence of a competing substrate, a swab soaked with sterile sheep's blood was applied to the skin and allowed to dry. The percentage of 104 Staph. aureus inoculum recovered allowed for comparison of the three products. In vitro, the 1% PVI formulation was bactericidal for 107 Staph. aureus within two minutes, as compared with the four minutes required by 10% PVI. On the skin contaminated with 106 organisms, the rates of killing within 30 seconds were comparable for both solutions. Application of blood onto the skin surface before contamination with 104 Staph. aureus resulted in a mean log reduction of 2.1 for 10% PVI as compared with 1.1 for 1% PVI. While 10% PVI remains the product of choice for disinfection in the presence of competing substrate, the chemically stable 1% formulation can be considered for routine handwashing by individuals for whom exposure to 10% PVI is irritating to the skin.