Trends in antibiotic resistance in Prevotella species from patients of the University Hospital of Maxillofacial Surgery, Sofia, Bulgaria, in 2003–2009

Head-and-neck infections often involve anaerobes such as Prevotella species. Aim of the present study was to assess the evolution and the factors associated with resistance in Prevotella species to penicillin, clindamycin, metronidazole, tetracycline and β-lactams/β-lactamase inhibitors (BL/BLIs). In total, 192 Prevotella strains, isolated from patients with oral and head-and-neck infections, were evaluated. Common isolates were Prevotella intermedia and Prevotella melaninogenica within the pigmented species as well as Prevotella oris and Prevotella oralis group within the non-pigmented species. Overall resistance was 43.2% for penicillin, 10.9% for clindamycin, 0% for metronidazole. Nonsusceptibility to tetracycline was 29.1% without significant differences in resistance rates between pigmented and other species. Penicillin resistant strains were β-lactamase positive. From 2003–2004 to 2007–2009, penicillin resistance rates increased about four-fold (from 15.4% to 60.6%). Clindamycin resistance did not show evolution, whereas tetracycline nonsusceptibility decreased from 43.3% in 2003–2004 to 20.7% in 2007–2009. Except for one (0.5%) P. oralis strain with intermediate susceptibility to BL/BLIs, the other strains were susceptible to the agents. In conclusion, in Prevotella strains from patients with head-and-neck infections, the resistance rate to penicillin increased, that to clindamycin remained stable and the nonsusceptibility rate to tetracycline decreased during the period. Activity against >99% of Prevotella strains was observed with metronidazole and BL/BLIs. The penicillin resistance and tetracycline nonsusceptibility were associated with the year of study, national antibiotic consumption and possibly with previous treatment (for tetracycline). The evolution of penicillin resistance in Prevotella strains was highly dynamic.