Prevotella intermedia/nigrescens group bacteria are Gram-negative, non-motile, anaerobic rods abundant in the subgingival microbiome of human periodontitis patients, and relatively sparse in persons with periodontal health. P. intermedia/nigrescens may be inadequately suppressed in periodontal pockets with conventional mechanical-surgical forms of periodontal therapy. Therefore, short-term systemic antibiotic therapy is often recommended in the treatment of recalcitrant (refractory) severe periodontitis patients where high numbers of P. intermedia/nigrescens persist in the subgingival microbiota. Limited available data suggests that the antibiotic sensitivity profile of periodontal P. intermedia/nigrescens has changed over time among severe periodontitis patients in the United States, with increasing levels of antibiotic resistance reported. These findings have potentially important clinical implications for dental professionals and their severe periodontitis patients which need further confirmation and clarification. To further expand knowledge on this clinically relevant issue, the purpose of the present study was to determine and compare over a 10-year period (2011 versus 2021) the prevalence of in vitro resistance of periodontal P. intermedia/nigrescens to the antibiotics amoxicillin, metronidazole, clindamycin, and doxycycline. / Oral Biology