Antimicrobial activities of thiolactomycin against gram‐negative anaerobes associated with periodontal disease

Thiolactomycin (TLM), (4R)‐(2E, 5E)‐2,4,6‐trimethyl‐3‐hydroxy‐2,5,7‐octatriene‐4‐thiolide, purified from a culture filtrate of a strain of the Nocardia species, was examined for antimicrobial activities against more than 100 strains of oral and periodontally associated bacteria. Nine other commonly used antibiotics were also included for the test. We found that TLM exhibited strong and selective antimicrobial activities against Bacteroides gingivalis and other oral black‐pigmented Bacteroides species that may be etiologically associated with adult periodontitis. TLM also inhibited the growth of Actinobacillus actinomycetemcomitans, but did not affect the growth of oral streptococcal species and Eubacterium species. Strains of Eikenella corrodens were moderately susceptible to TLM, while Actinomyces viscosus strains were only slightly susceptible to it. Other antibiotics used for comparison showed a broad spectrum of antimicrobial activities in general. In conclusion, TLM exhibited highly selective antimicrobial activities to black‐pigmented Bacteroides species and A. actinomycetemcomitans, both of which are implicated in the pathogenesis of human periodontal disease.