Long‐term effects of tetracyline on the subgingival microflora

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Abstract
The long‐term effect of tetracycline therapy on the subgingival microbiota was studied in a single patient, a 33‐year‐old female with advanced periodontal disease. Prior to antibiotic therapy, two initial plaque samples were collected to establish the baseline microbial data. These untreated samples contained high numbers of small and medium‐sized spirochetes together with anaerobic Gram‐negative rods including Bacteroides asac‐charolyticus, Fusobacterium nucleatum, anaerobic “corroding” rods resembling the species B. corrodens but lacking a positive urease reaction, and a group of unidentified, non‐fermenting anaerobic rods. The anaerobic asaccharolytic coccus, Peptostreptococcus micros, was also present as 7–10 % of the pretreatment flora. This complex, largely Gram‐negative flora was changed to a facultative, saccharolytic plaque of streptococci (5. mitis and S. mutans) and actinomyces (A. viscosus and A. naeslundit) within 2 weeks of tetracycline therapy at 1000 mg per day. Rothia dentocariosa was the dominant organism cultured after an additional 2 weeks of 500 mg tetracycline per day. Of the predominant pretreatment flora, Fusobacterium nucleatum and Peptostreptococcus micros returned 6–8 weeks following therapy. The known pathogenic associations of this pair of organisms are discussed. However, there were no clinical manifestations of the recolonization by these organisms. Small spirochetes were observed, but not numerous, beginning 16 weeks after therapy. Two groups of organisms currently considered important in periodontal destruction, B. asaccharolyticus and the anaerobic “corroding” bacilli, did not return during the period of observation. High levels of tetracycline resistance were common among the Gram‐positive cocci isolated during treatment.