Antibiotic Resistance Changes in Periodontal Parvimonas micra Over 10 Years

Objectives: Despite world-wide concerns about increasing levels of antibiotic resistance in the human microbiome, no surveillance data are presently available on changes over time in the antibiotic resistance profile of specific periodontal microorganisms. This study examined temporal changes over a 10-year period in the in vitro resistance of periodontal Parvimonas micra to antibiotic breakpoint concentrations of doxycycline, amoxicillin, metronidazole, and clindamycin, which are often employed in various periodontal treatment regimens.
Methods: Subgingival plaque biofilms culture-positive for P. micra from 300 consecutive adults with severe chronic periodontitis in the USA in 2006 and 2016 were plated onto enriched Brucella blood agar supplemented with either 4 mg/L of doxycycline or clindamycin, 8 mg/L of amoxicillin, or 16 mg/L of metronidazole (representing non-susceptible/resistant antibiotic breakpoint concentrations), followed by anaerobic incubation. P. micra isolates growing on antibiotic-supplemented media were considered drug-resistant, as previously described (Rams et al. 2014). Fisher's exact test compared among patients the presence of P. micra in vitro resistance in 2016, as compared to 2006, to each of the tested antibiotics.
Results: P. micra in vitro resistance was significantly more frequent among patients in 2016, as compared to 2006, for doxycycline (11.3% vs. 0.3% positive patients; 37.7-fold increase), and clindamycin (47.3% vs. 2.0% positive patients; 23.7-fold increase) (both P < 0.0001). In contrast, the prevalence of P. micra resistance to amoxicillin (2.3% vs. 1.0% positive patients) and metronidazole (0% vs. 0.3% positive patients) remained low and statistically unchanged over the 10-year period (P > 0.05).
Conclusions: Marked and alarming increases were found over a 10 year period in the in vitro resistance of periodontal P. micra to doxycycline and clindamycin, but not to amoxicillin or metronidazole. These findings raise serious questions about empiric use of doxycycline or clindamycin, either locally or systemically, in periodontal treatment of patients harboring subgingival P. micra.