Minimizing antibiotic resistance is a key motivation strategy in designing and developing new and combination therapy. In this study, a combination of the antibiotics (cefixime, levofloxacin and gentamicin) with Lysobacter enzymogenes (L. enzymogenes) bioactive proteases present in the cell- free supernatant (CFS) have been investigated against the Gram-positive methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA) and the Gram-negative Escherichia coli (E. coli O157:H7). Results indicated that L. enzymogenes CFS had maximum proteolytic activity after 11 days of incubation and higher growth inhibitory properties against MSSA and MRSA compared to E. coli (O157:H7). The combination of L. enzymogenes CFS with cefixime, gentamicin and levofloxacin at sub-MIC levels, has potentiated their bacterial inhibition capacity. Interestingly, combining cefixime with L. enzymogenes CFS restored its antibacterial activity against MRSA. The MTT assay revealed that L. enzymogenes CFS has no significant reduction in human normal skin fibroblast (CCD-1064SK) cell viability. In conclusion, L. enzymogenes bioactive proteases are natural potentiators for antimicrobials with different bacterial targets including cefixime, gentamicin and levofloxacin representing the beginning of a modern and efficient era in the battle against multidrug-resistant pathogens.
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