Inhibitory effect of Brazilian red propolis on planktonic and biofilm forms of Clostridioides difficile

Clostridioides difficile is a Gram-positive, spore-forming, anaerobic bacillus which is the leading cause of health-care-associated infective diarrhea. The rising incidence of antibiotic resistance in pathogens such as C. difficile makes researches on alternative antibacterial products very important, especially those exploring natural products like propolis. Brazilian Red Propolis, found in the Northeast region of Brazil, is composed by products from regional plants that have the antimicrobial properties. This study aimed to evaluate the in vitro activity of Brazilian Red Propolis (BRP) against C. difficile strains in planktonic and biofilm forms. The susceptibility of four strains of C. difficile to BRP was analyzed by broth microdilution method and vancomycin was included as control drug. BRP-exposed C. difficile cells were evaluated by scanning electron microscopy (SEM). Then, the effects of BRP on growing and mature C. difficile biofilms were also evaluated. BRP minimum inhibitory concentration was 625 μg/mL against all tested strains, while vancomycin MIC range was 0.5-2 μg/mL. SEM showed the loss of homogeneity in bacterial cell wall and cell fragmentation, after BRP-exposure. BRP, at MIC, reduced (P < 0.05) the biomass, matrix proteins and matrix carbohydrates of growing biofilms, and, at 8xMIC, reduced (P < 0.05) the biomass and matrix proteins of mature biofilms. The present study demonstrated that BRP inhibits planktonic growth, damages cell wall, decreases biofilm growth and harms mature biofilms of C. difficile.