2306 Doxycycline Resistance in Periodontal Peptostreptococcus micros
T.E. RAMS1, M.A. SWAID1, D. FEIK1, and A.J. VAN WINKELHOFF2, 1Temple University School of Dentistry, Philadelphia, PA, USA, 2Academic Centre for Dentistry Amsterdam (ACTA), Netherlands

Objectives: Peptostreptococcus micros is a periodontal pathogen reported to resist subgingival eradication by conventional mechanical forms of periodontal therapy. Since adjunctive antimicrobial therapy may therefore be indicated for P. micros periodontal infections, the occurrence of in vitro resistance to therapeutic levels of doxycycline, clindamycin, amoxicillin and metronidazole was determined among clinical P. micros isolates from 300 consecutive organism-positive severe human periodontitis subjects in the United States. Methods: Pooled subgingival plaque specimens from each study subject were transported in VMGA III, and plated onto enriched Brucella blood agar (EBBA), and onto EBBA supplemented with either 4 g/ml of doxycyline or clindamycin, 8 g/ml of amoxicillin, or 16 g/ml of metronidazole (representing NCCLS non-susceptible breakpoint concentrations), followed by anaerobic incubation. P. micros isolates were identified as gram-positive, non-motile, anaerobic cocci exhibiting milk-white, circular, dome colonies under a magnification loupe. In vitro antibiotic resistance was noted as P. micros growth on both antibiotic-supplemented and non-supplemented EBBA. Results: P. micros recovery averaged 11.8 % (range 0.1-55.3%) of total cultivable anaerobic counts on non-supplemented EBBA among all study subjects. 71 (23.7%) subjects yielded P. micros resistant to 4 g/ml doxycycline, with resistant isolates averaging 14.1% of total anaerobic counts in positive subjects, and occurring independent of subject gender. Subjects harboring doxycycline-resistant P. micros were significantly younger than persons with doxycycline-susceptible P. micros (P = 0.002). In vitro P. micros resistance was rare to metronidazole (0.7% of subjects) and clindamycin (1.3% of subjects), and not detected to amoxicillin in the periodontitis subjects studied. Conclusions: Doxycycline-resistant P. micros clinical isolates were recovered from approximately one in four human periodontitis patients studied, particularly among the younger-aged, whereas in vitro resistance to metronidazole, clindamycin and amoxicillin was rare or undetected. Due to the frequent occurrence of doxycycline-resistant strains, laboratory susceptibility testing in treatment of P. micros-associated periodontitis seems necessary.

Seq #249 - Microbes, Models, and Responses
2:00 PM-4:00 PM, Friday, 11 March 2005 Baltimore Convention Center Exhibit Hall E-F

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