Cultured microbial community complexity is associated with antimicrobial resistance and Enterobacterales enrichment in adult odontogenic infections

Odontogenic infections are polymicrobial entities with increasing antimicrobial resistance. Although immunosuppression is commonly considered a major risk factor for resistant and complex infections, concepts from microbial ecology suggest that community complexity itself may be associated with distinct microbial phenotype and susceptibility patterns. We performed a retrospective cohort study of consecutive patients undergoing surgical treatment for odontogenic infections at a tertiary maxillofacial center between 2017 and 2022. Intraoperative specimens were processed using standardized aerobic and anaerobic culture protocols. Primary outcomes were polymicrobial infection, Enterobacterales detection, and antimicrobial resistance; MRSA and Candida spp. were secondary outcomes. Immunosuppression was defined by systemic immunosuppressive therapy, chemotherapy, solid organ transplantation, or HIV infection. Cultured microbial community complexity was operationalized as the number of distinct pathogens detected by routine culture in each patient. Among 695 included patients, polymicrobial infection was detected in 62.0% and antimicrobial resistance in 40.6%, without differences by immune status. Enterobacterales were more frequently detected in immunosuppressed patients (13.9% vs. 3.9%). Unsupervised clustering of pathogen profiles did not segregate by immune status. High microbial complexity was associated with a distinct microbiological profile associated with near-universal polymicrobial infection (97.2% vs. 55.3%), increased antimicrobial resistance (72.9% vs. 34.8%), and marked Enterobacterales enrichment (19.6% vs. 2.9%) (all p < 0.001). In fully adjusted models, higher cultural microbial complexity showed the strongest adjusted association with all adverse microbiological outcomes, whereas no independent association was observed for the broad immunosuppression variable used in this study. Dose–response analyses demonstrated a graded increase in Enterobacterales detection and antimicrobial resistance with rising pathogen burden. In this retrospective cohort of surgically treated odontogenic infections, higher cultured microbial complexity was strongly associated with polymicrobial infection, Enterobacterales detection, and antimicrobial resistance. These findings support support further investigation of community-level microbiological features for future risk stratification approaches.