[Germicidal experiments with aqueous PVP-iodine-containing disinfecting solutions: effect of the content of free iodine on the bactericidal action against Staphylococcus aureus].

The bactericidal activity against Staph. aureus of three PVP-iodine preparations in different concentrations, and of 0.1 mol/L KI-solutions with concentrations of free iodine corresponding to the povidone-iodine preparations, was evaluated at reaction times of 7, 15, 30 and 60 seconds. The concentration of free iodine has been measured potentiometrically during the entire reaction time. In all cases it has been confirmed that the bactericidal activity is increasing with the concentration of free iodine. However, there have been found differing correlations between the logarithmic decrease of germs (RF-value), the concentration of free iodine and the reaction time (statistical evaluation of the results by means of linear multiple regression: RF = a0 + a1 log [I2] + a2 log t). Referring to the concentration of free iodine the bactericidal activity in the range of RF approximately equal to 4-6 is increasing as follows: Povidone-iodine washing concentrate much greater than iodine in KI (0.1 mol/l) greater than Povidone-iodine mucosal disinfectant greater than aqueous solution of povidone iodine. This sequence is explained by differences of composition. So it is assumed that the surface active ingredients facilitate the penetration of molecular iodine. The observed correlations show that there is probably no exact mathematical relation of general validity for iodine preparations of different composition between the concentration of free iodine and the RF-value. However, for one and the same preparation such a correlation can be derived and enables to make predictions about the bactericidal activity, which can be expected as a consequence of the concentration of free iodine.