The efficacy of antimicrobial therapies in the treatment of mixed biofilms formed between Candida albicans and Porphyromonas gingivalis during epithelial cell infection in the aspiration pneumonia model

Aspiration pneumonia is a serious respiratory condition, which is particularly prevalent in patients with dysphagia, neurological disorders, or those undergoing surgical interventions. The formation of multispecies biofilms in the oral cavity, involving the bacterial periodontopathogen Porphyromonas gingivalis and the opportunistic pathogenic fungus Candida albicans, may also be related to the development of this serious disease, contributing also to the resistance to standard antimicrobial treatment. Therefore, this research aimed to evaluate the efficacy of selected antibiotics-levofloxacin, metronidazole, meropenem, vancomycin-and antifungal agents-amphotericin B, caspofungin, and fluconazole-on these mixed biofilms in the aspiration pneumonia model. While metronidazole and levofloxacin effectively inhibited bacterial viability in the mixed biofilms, lower doses increased release of bacterial proteases. In the conditions of mixed biofilms meropenem and vancomycin showed reduced efficacy, requiring significantly higher doses to achieve similar effect in mixed biofilms as in single bacterial cultures. Treatment with antifungals revealed that amphotericin B significantly impacted fungal cell viability within mixed biofilms, and this effect was enhanced when the antifungal drug was applied in the presence of P. gingivalis. Caspofungin and fluconazole showed variable efficacy, with caspofungin being more effective against C. albicans cells within biofilm.These findings indicated that due to the mutual microbial protection in the mixed-species biofilm, P. gingivalis retained its virulence despite increasing antibiotic doses. However, no excessive benefit of mixed biofilms was observed for C. albicans in the presence of antifungals, indicating the minor importance of yeasts in aspiration pneumonia development and their protective role for other pathogens in mixed-species infection.