Phage therapy for refractory periapical periodontitis caused by Enterococcus faecalis in vitro and in vivo

A phage PEf771 that specifically infects and lyses pathogenic Enterococcus faecalis YN771 in patients with refractory periapical periodontitis was used to investigate resistance against E. faecalis infection in vitro and in vivo. PEf771 completely lysed YN771 within 3 h, with a multiplicity of infection of 1. Compared with ten routinely used clinical antibiotics, PEf771 demonstrated the highest bacteriostatic effect within 72 h. The antibacterial effect of PEf771 on extracted teeth within 72 h was better than that of conventional root canal disinfectants such as camphorated phenol, formaldehyde cresol solution, and Ca(OH)₂ (P < 0.05) within 72 h. Using E. faecalis, intraperitoneal and periapical infection models were established using Sprague Dawley (SD) rats. The results showed that all SD rats inoculated with 9.6 × 10¹¹ CFU/mL E. faecalis YN771 or 2.9 × 10¹¹ CFU/mL E. faecalis RYN771 died within 8 h. Additionally, all SD rats inoculated with YN771 and treated with antibiotics died within 72 h. Although SD rats inoculated with RYN771 and treated with antibiotics survived for 72 h, the pathological anatomy of these rats showed purulent discharge, numerous pus and blood-filled ascites, and extensive liver abscesses. Notably, YN771 rats treated with PEf771 and RYN771 rats treated with RPEf771 survived for 72 h, and their pathological anatomy showed that the liver, kidneys, intestine, and mesenteries were normal. Computed tomography analysis of SD rats infected with periapical periodontitis showed pathological changes in experimental teeth inoculated with YN771, despite undergoing a normal root canal treatment. Contrastingly, none of the experimental teeth exhibited root periapical inflammation following PEf771 treatment. Hematoxylin and eosin staining revealed a gap between the periodontal ligament and the cementum of experimental teeth, whereas PEf771-treated teeth exhibited normal results. These findings suggested that phage therapy using PEf771 might effectively prevent E. faecalis infection after root canal treatment.Key points• Compared with common clinical antibiotics, PEf771 showed the highest antibacterial.• The liver, kidney, intestine, and mesentery of SD rats treated with PEf771 were normal.• Phage therapy can effectively prevent E. faecalis YN771 and RYN771 infection.