Eight year persistence of individual differences in the bacterial flora of the forehead.

Eight subjects having a rich (greater than or equal to 100,000 per cm2) population of Propionibacterium acnes on the forehead and 7 with a sparse population (great than or equal to 15,000 per cm2) in earlier tests were reexamined after median interval of 8 yr. All of those with an initial rich population had greater than or equal to 100,000 per cm2 on retest. Of the 7 with an initial sparse population, 4 again had fewer than 15,000, one had more than 100,000 per cm2 and 2 were intermediate. Three subjects harbored Peptococcus saccharolyticus in the initial test (26,000 to 75,000 per cm2) and all 3 carried this organism on the later test (5,000 to 49,000 per cm2). Of the 12 without P. saccharolyticus initially, 11 were again negative and one had a small number (200 per cm 2). We conclude that the presence or absence of P. saccharolyticus and the relative population density of P. acnes were individual characteristics that persisted in most subjects for at least 8 yr.