Evaluation of the antibacterial activity of stem cells from apical papilla and their conditioned medium against Escherichia coli and Staphylococcus aureus.

Human mesenchymal stem cells (hMSCs) are versatile cells obtained from various regions of the human body. Beyond their potential for cell replacement, MSCs secrete a wide range of growth factors and cytokines and have recently been recognized for their potent antibacterial activity, representing a promising approach to combat bacterial infections. This study is the first to evaluate the antibacterial properties of stem cells from apical papilla (SCAPs) and their conditioned medium (CM) against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) using colony count and disk diffusion assays. The minimum inhibitory and bactericidal concentrations were determined through serial dilutions of SCAP-CM, and the expression of antibacterial and immunomodulatory genes was analyzed by qRT-PCR. Both SCAPs and human foreskin fibroblasts (HFFs) exhibited antibacterial activity, as shown by CFU and disk diffusion assays, with SCAP-CM demonstrating greater efficacy. The minimum bactericidal concentrations of SCAP-CM against E. coli and S. aureus were 2.5 mg/ml for both, compared to 80 mg/ml and 320 mg/ml for HFF-CM, respectively. SCAPs showed increased expression of antibacterial and immunomodulatory genes in response to both bacterial strains, whereas HFFs displayed reduced IL1β and variable changes in IL6 and TNFα depending on the strain. The antibacterial effect was partially attributed to secretion of the LL-37 peptide. These findings confirm SCAPs exhibit potent antibacterial activity against both Gram-negative and Gram-positive bacteria, mediated by soluble immunoregulatory factors, with inhibitory effects comparable to gentamicin and distinct from those of HFFs. They provide mechanistic insight into SCAP-derived antimicrobial responses and highlight their potential as antibiotic-sparing therapeutic strategies.