The bacteria within open and closed comedones were evaluated quantitatively and the cocci classified by the Baird-Parker scheme. Corynebacterium acnes and gram positive cocci were always present. The anaerobes greatly outnumbered the aerobes in both types. C acnes was more numerous in closed comedones. Staphylococcus type II (SII) was the predominant member of the coccal flora. Micrococcus isolates were rare.
Izumi AK, Marples RR, Kligman AM. Bacteriology of Acne Comedones. Arch Dermatol. 1970;102(4):397-399. doi:10.1001/archderm.1970.04000100045010