Abstract
The susceptibility of eighty F. nucleatum isolates from periodontal patients, healthy subjects and Cebus apella monkeys to human pooled sera was tested. The resistance to serum bactericidal effects was observed in 46.9% of the isolates from periodontal patients, 28.6% of the healthy subjects and 40% of the monkeys. These results support the hypothesis that serum plays an ecological role by controlling the microbial population inside either the gingival crevice or periodontal pocket.