Two Strains of Endophytic Bacillus velezensis Carrying Antibiotic-Biosynthetic Genes Show Antibacterial and Antibiofilm Activities Against Methicillin-Resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) is considered a priority pathogen causing high mortality that requires effective control measures. This study aimed to detect the presence of antibiotic-biosynthetic genes and to evaluate the anti-MRSA activity of two strains of endophytic Bacillus velezensis isolated from Archidendron pauciflorum. PCR-based screening showed that B. velezensis strains, such as DJ4 and DJ9 possessed six antibiotic-biosynthetic genes, namely MlnA, DhbE, BacD, DfnD, SrfA, and BaeR. According to the preliminary test conducted using disc-diffusion assay, metabolite extracts from these strains have anti-MRSA activity with clear zone diameters of 13.00 ± 0.82 mm, and 17.33 ± 0.47 mm, respectively. Extract from DJ9 strain was more active to MRSA, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 62.50 µg/mL and 250 µg/mL, respectively. Furthermore, a bactericidal effect was observed, as evidenced by MBC/MIC ratio of four. Both DJ9 and DJ4 extracts showed a dose-dependent inhibitory effect on MRSA biofilm formation. Furthermore, a maximum inhibition percentage of 60.12 ± 2.5% was shown by DJ9 extract in two-fold MIC. The corresponding extract disrupted MRSA mature biofilms most effectively at 55.74 ± 1.4%. In conclusion, crude extract, particularly the DJ9 strain had significant potential in inhibiting MRSA cell growth, MRSA biofilm formation, and disrupting MRSA mature biofilm in vitro.