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Background: Given the global problem of antibiotic resistance among pathogens, researchers are looking for appropriate treatment alternatives to eliminate infections. Application of probiotics and their products can be a practical solution. This study aimed to investigate the inhibitory effect of cell-free supernatant (CFS) of probiotics against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Methods: The effect of CFS of eight strains of probiotics against E. coli and S. aureus was evaluated by well diffusion method. The agent with the highest inhibition diameter was selected to investigate other antibacterial properties. They included minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and timed kill effect. Surface electron micrographs were taken to compare the treated versus untreated bacteria with CFS of Lactobacillus acidophilus (SLA) LAFTI-L10 DSL. Finally, the percent viability of the Hu02 cells was investigated after 24, 48 or 72 hours of incubation with SLA at various concentrations. Results: Among the tested strains, SLA showed the highest inhibitory diameter against E. coli and S. aureus (P=0.005). Also, the MIC of SLA was equal to those of E. coli and S. aureus (12.5 mg/mL) but was different in their MBC. Almost 100% of bacteria removed after exposure to SLA (20 min.). The results of log CFU/mL demonstrated that SLA had bactericidal effect against S. aureus and E. coli. The toxicity assays showed that the percent viability of the Hu02 cells was 31.71 to 81.09 after 24, 48 or 72 hours exposure. Conclusions: Our results suggest that SLA can be a suitable, effective and safe alternative to antibiotics. [ABSTRACT FROM AUTHOR]

Background: The emergence of multidrug resistance among nosocomial pathogens has prompted researchers to look for new antibacterial sources. Metal nanoparticles and probiotic products have attracted the attention of researchers. However, combination therapy is an attractive alternative in this field., Objectives: This study evaluated the antibacterial activity and toxicity of Zinc Oxide nanoparticles (ZnO-NPs) combined with cell-free supernatant (CFS) of Lactobacillus plantarum and Lactobacillus acidophilus alone and in a novel mixture., Methods: Antibacterial effects and cytotoxic properties of ZnO-NPs, CFS of L. plantarum (SLP), and CFS of L. acidophilus (SLA) were determined alone and in a mixture against ESKAPE strains. In addition, the viability percentage of the cells was evaluated after exposure to these agents., Results: Antibacterial mixtures (ZnO-NPs with SLP or ZnO-NPs with SLA) demonstrated synergistic and additive effects against Pseudomonas aeruginosa (FIC≤0.75), Acinetobacter baumannii (FIC = 1), and Escherichia coli (FIC≤0.75). The viability percentage of the cells after 24 h of exposure to a mixture of ZnO-NPs and SLA (about 50%) was more than when the cells were exposed to ZnO-NPs alone (about 30%) at the same concentration., Conclusions: A mixture of ZnO-NPs and CFS of probiotics can be an alternative to antibiotics, with more effectiveness and fewer side effects., Competing Interests: The authors have no conflict of interest., (Copyright © 2023, Soleymanzadeh et al.)