Introduction: Osteosarcomas of the jaw (OSJ) are rare tumors with a different behavior from osteosarcomas of other bones. This study aims to analyze the clinical, pathological, and therapeutic characteristics of this type of sarcoma. Methods: a retrospective observational study of cases diagnosed with OSJ registered at the “La Paz” University Hospital (Madrid). Results: Eight cases with a diagnosis of OSJ were obtained in a study period of 22 years (2000-2022). The mean age was 41 years. The distribution was 1:1 between the maxilla and mandible. Painful inflammation was the most frequent clinical manifestation. Conventional osteoblastic osteosarcoma was the most common. Survival at 5 years was 50%, while at 10 years, it decreased to 25%. Conclusions: OSJ differs from conventional osteosarcomas of long tubular bones. Surgery continues to be the mainstay of treatment; more studies are needed in which more standardized protocols can be proposed for adjuvant therapeutic management.

The global health emergency caused by multi-drug resistant bacteria has led to the search for and development of new antimicrobial agents. Phage therapy is an abandoned antimicrobial therapy that has been resumed in recent years. In this study, we mutated a lysogenic phage from Acinetobacter baumannii into a lytic phage (Ab105-2phiΔCI) showing antimicrobial activity against A.baumannii clinical strains (such as Ab177_GEIH-2000 which showed MICs to meropenem and imipenem of 32 µg/ml and 16 µg/ml, respectively as well as belonging to GEIH-REIPI Spanish Multicenter A. baumannii Study II 2000/2010, Umbrella Genbank Bioproject PRJNA422585). We then enhanced the time kill curves (in vitro) and in Galleria mellonella survival assays (in vivo) antimicrobial activity of the new lytic phage by combining it with carbapenem antibiotics (meropenem and imipenem). We observed in vitro, an antimicrobial synergistic effect (from 4 log to 7 log CFU/ml) with meropenem plus lytic phage in all combinations analysed (0.1, 1 and 10 MOI of Ab105-2phiΔCI mutant as well as 1/4 and 1/8 MIC of meropenem). Moreover, we had a decrease in bacterial growth of 8 log CFU/ml for the combination of imipenem at 1/4 MIC plus lytic phage (Ab105-2phiΔCI mutant) and of 4 log CFU/ml for the combination of imipenem at 1/8 MIC plus lytic phage (Ab105-2phiΔCI mutant) in both MOI 1 and 10. These results were confirmed in in vivo (G. mellonella) obtaining a higher effectiveness in the combination of imipenem and Ab105-2phiΔCI mutant (P<0.05 by Log Rank-Matel Cox test). This approach could help to reduce the emergence of phage resistant bacteria and restore sensitivity to the antibiotics when used to combat multiresistant strains of Acinetobacter baumannii.