Involvement of resistant bacteria in the severity of refractory osteonecrosis of the jaw.

Purpose: Osteoradionecrosis (ORN) and medication-related osteonecrosis of the jaw (MRONJ) are relatively rare and refractory, and there is no consensus regarding the bacteria associated with their development. This study was conducted to identify the bacteria associated with refractory ORN and MRONJ, including severe cases.

Methods: Patients who underwent surgery for osteonecrosis of the jaw were included in this study. Bacterial culture specimens were obtained from tissue as deeply as possible. Severe cases of ORN and MRONJ were defined as stage IV of Lyon's classification and stage III of the AAOMS classification, respectively. Demographic data, clinical features, antimicrobials usage, and bacteria detected were analysed to determine the factors associated with severe disease.

Results: Seventy-seven patients (ORN, n = 22; MRONJ, n = 55) were analysed. Penicillins were the most commonly used antimicrobials. A total of 311 bacterial strains were detected in tissue culture (detection rate = 100%). Streptococcus spp. were the most common bacteria (37.0%), followed by anaerobes (33.8%). Gram-negative rods were detected in 10.3% of the patients, antimicrobial-resistant bacteria in 78.4%, and ampicillin resistance in 60.8%. Factors associated with severe disease were ampicillin resistance and malignancy in MRONJ, with odds ratios of 8.74 (95% confidence interval, 1.20-63.4; p = 0.032) and 13.5 (1.09-168, p = 0.043), respectively. Enterobacter spp. were detected only in severe cases.

Conclusion: Bacteria associated with osteonecrosis of the jaw are similar in composition to those responsible for common odontogenic infections, but with a higher proportion of gram-negative rods. Ampicillin-resistant bacteria, including Enterobacter spp., are implicated in severe disease.