Background: Medication-related osteonecrosis of the jaw (MRONJ) is a common adverse event following antiresorptive treatment, leading to chronic inflammation and exposed, necrotic bone surfaces in the jawbone. There is an increasing recognition of the role of compositional changes in the colonizing members of the oral microbiota implicated in triggering and/or maintaining MRONJ. The aim of our study was to characterize the culturable and non-culturable microbiota—with particular focus on
Actinomyces spp. and
Actinomyces-like organisms (ALOs)—from surgically removed bone samples of MRONJ patients and healthy control subjects.
Methods:
n = 35 patients (median age: 70 years) in various stages of MRONJ, with a history of receiving oral or intravenous antiresorptive treatment were included in the study. The controls (
n = 35; median age: 35 years) consisted of otherwise healthy individuals undergoing tooth extraction. Traditional, quantitative, aerobic, and anaerobic culture, and
Actinomyces-specific PCR was performed for all bone samples from patients and controls, while microbiome analyses—based on 16S rRNA sequencing—were carried out in 5-5 randomly selected samples. Mann–Whitney U test, Wilcoxon rank sum test (alpha diversity), and PERMANOVA analysis (beta diversity) were performed.
Results: In MRONJ samples, 185 anaerobic isolates, corresponding to 65 different species were identified (vs. 72 isolates, corresponding to 27 different species in the control group). The detection of
Actinomyces spp. and ALOs was more common in MRONJ bone samples, based on traditional culture (65.7% vs. 17.1%;
p < 0.001) and PCR (82.9% vs. 37.1%;
p < 0.001), respectively. The isolation of
Fusobacterium spp. (22 vs. 7;
p = 0.001),
Prevotella spp. (22 vs. 6;
p = 0.034), and Gram-positive anaerobic cocci (GPAC) (30 vs. 9;
p = 0.016) was significantly more common in MRONJ patient samples. The microbiota of the controls’ bone samples were characterized by a considerable dominance of
Streptococcus spp. and
Veillonella spp, while the bacterial abundance rates were substantially more heterogeneous in MRONJ bone samples. Notable differences were not observed among the samples related to the abundance of
Actinomyces in the bone microbiota.
Conclusions: According to the “infection hypothesis”, alterations in the oral microbiome—with
Actinomyces and ALOs being the most relevant—may play a key role in the development, aggravation, and progression of MRONJ. The timely detection of
Actinomyces in necrotic bone is crucial, as it has important therapeutic implications.
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