In vivo standardization of cutaneous bactericidal activity of antiseptics by using monoxenic hairless mice

This study was designed to investigate the bactericidal activities of antiseptics on the cutaneous flora of hairless mice monoxenic to Staphylococcus epidermidis, Staphylococcus aureus, or Pseudomonas aeruginosa in vivo. A standardized method for testing such antiseptics to compare their bactericidal effectiveness in humans in described. Seven antiseptics belonging to seven different chemical groups (iodine derivatives, alcohols, mercury compounds, quaternary ammonium salts, biguanides, phenols, and carbanilides) were used as recommended by the manufacturers (conditions of contact or prolonged contact time followed by washing with distilled water). Germfree hairless mice were infected with various bacterial strains by gastric intubation, producing levels of about 10(3) CFU/cm2 of skin. The antiseptic under test was placed on the right or left side of the ventral region. The contralateral side served as a control. In order to standardize the method, a number of crucial parameters were carefully controlled: the amount of antiseptic applied, the area of skin treated, the duration of treatment, and the washing procedure. Skin samples were obtained by cutaneous biopsy, which effectively removed all the bacteria along with the sample. The bacterial populations were counted before and after application of the antiseptic. Reductions of between 0.5 and 1.9 log units were obtained; these are comparable to those observed in humans. The standardization of our procedure and the use of animals with a strictly controlled flora eliminated much of the variability and sources of error inherent in human studies. This model could be of value for the study of resistant bacterial strains responsible for nosocomial infections and for investigations of damaged skin.