Changes in the prevalence of subgingival enteric rods, staphylococci and yeasts after treatment with penicillin and erythromycin.

The changes in the balance of microbial flora in the periodontium after antibiotic treatment were investigated in a blind study. The prevalence of gram-negative enteric rods, staphylococci and yeasts was followed before and during penicillin or erythromycin treatment of 72 periodontitis patients without periodontal cleaning. The prevalence of subgingival coagulase-positive staphylococci increased significantly following systemic penicillin therapy. After systemic erythromycin therapy, the prevalence of subgingival gram-negative enteric rods increased. Ten of 24 (42%) patients receiving systemic penicillin therapy developed clinical evidence of periodontal abscesses. In the absence of conventional mechanical cleaning, systemic administration of penicillin and erythromycin antibiotic to patients with pre-existing periodontitis may lead to periodontal superinfection with opportunistic organisms.