Comparison of red complex bacteria and antimicrobial resistance genes in stage III/IV periodontitis patients with and without type 2 diabetes mellitus: A cross-sectional observational study

Background and objectives Type 2 diabetes mellitus (T2DM) impairs host immunity, increases infection susceptibility, and may promote antimicrobial resistance. Periodontitis and T2DM share a bidirectional relationship, influencing both periodontal breakdown and metabolic control. This study aimed to compare red complex periodontal pathogens and antimicrobial resistance genes ( bla TEM and nim ) in stage III/IV periodontitis patients with and without T2DM. Materials and methods This cross-sectional observational study included 68 participants recruited using consecutive sampling and divided into two groups: Stage III/IV periodontitis patients without diabetes (n = 34) and Stage III/IV periodontitis patients with type 2 diabetes mellitus (T2DM) (n = 34). Periodontal parameters (plaque index, bleeding index, probing depth, and clinical attachment level) were recorded. Subgingival plaque samples were analyzed using polymerase chain reaction (PCR) to detect red complex bacterial genes and resistance genes ( bla TEM , nim ). Statistical significance was set at p < 0.05. Results Probing depth and clinical attachment level were significantly higher in the periodontitis + T2DM group (p = 0.001). The nim gene was detected exclusively in diabetic patients (26.5%, p = 0.002), while bla TEM prevalence was similar in both groups (p = 0.75). No significant differences were observed in red complex bacterial detection between groups (p > 0.05). Conclusion The exclusive detection of the nim resistance gene in Stage III/IV periodontitis patients with T2DM may indicate an association between type 2 diabetes mellitus and the presence of metronidazole resistance determinants within periodontal biofilms. However, this observation should be interpreted cautiously because the cross-sectional design and relatively small sample size limit the strength and generalizability of the evidence.