In Vitro evaluation of cell-free supernatants from soil-derived Bacillus sp. for antibiofilm and antioxidant activities.

BACKGROUND

Methicillin-resistant S. aureus (MRSA) causes serious infections, as bacterial biofilms play a significant role in recurrent or chronic infections. Therefore, novel therapeutic approaches are required to combat MRSA resistance.

METHODS

This study tested the ability of a cell-free supernatant (CFS) of Bacillus sp. isolated from licorice roots to inhibit MRSA biofilms. The impact of Bacillus CFS on the expression of biofilm-associated genes was examined. The antioxidant and anti-inflammatory activities of CFS were evaluated, as well as its cytotoxicity in vitro using human skin fibroblasts (HSF). Bacillus sp. was identified using 16 S rRNA sequence analysis and deposited in a local culture collection as Bacillus sp. CCASU-C91.

RESULTS

The results revealed Bacillus sp. susceptibility to different classes of antibiotics. GC-mass analysis of CFS revealed the presence of various compounds, including fatty acids, phenolic compounds, and sesquiterpenes. Additionally, CFS exhibited concentration-dependent antioxidant and protein anti-denaturation activities in vitro, albeit at lower potency than reference standard. And inhibited the growth of MRSA with a minimum inhibitory concentration (MIC) ranging from 62.5 µg/mL to 250 µg/mL. In addition, time-kill curves showed that CFS at (2MIC) concentration could kill more than half of the MRSA strains within 4 h. In addition, CFS inhibited biofilm formation and reduced preformed biofilm biomass by more than 90%. Notably, Bacillus CFS decreased the expression of MRSA biofilm genes(icaA, icaD and ebps) at 0.5 MIC. Cytotoxicity assay revealed an IC50 value of 1029 ± 20.2 µg/mL for Bacillus CFS.

CONCLUSION

These preliminary in vitro findings indicate that Bacillus CFS possesses anti-MRSA activity, supporting further investigation into its potential therapeutic applications.