In vitro and in vivo synergy of Vancomycin and β-lactams against drug-resistant Mycobacterium tuberculosis and Non-tuberculous mycobacteria

The unabated increase in antimicrobial resistance has underlined the importance of identifying novel drug combinations which eliminate infections more potently and likely reduce the emergence of resistance. In this context, we have identified Vancomycin and many β-lactams as being potently active against drug-resistant Mycobacterium tuberculosis and non-tuberculous mycobacteria including M. abscessus, emerging as pathogens of concern owing to their inherent drug resistance profile. In this study, we have identified combinations of Vancomycin, a glycopeptide and β-lactams, especially Ceftriaxone, Ceftazidime and Meropenem, in the presence or absence of Sulbactam, a β- lactamase inhibitor, as possessing potent antimicrobial activity against several drug-resistant mycobacterial strains. The combination of Vancomycin and β-lactams exhibited potent bactericidal activity and reduced the bacterial load better than either drug alone. The molecular basis of synergy was mediated by increase in permeability of mycobacterial cell as demonstrated by ethidium bromide assay. In the murine model of mycobacterial infection, synergistic combination of Vancomycin and β-lactams outperformed clinically utilized drugs including Isoniazid, Rifampicin and Ethambutol against M. tuberculosis and Amikacin, Clarithromycin against M. abscessus . The combinations caused a significant reduction in bacterial load in various organs in M. tuberculosis and M. abscessus infected mice. Thus, the synergistic combination of Vancomycin and β-lactams could potentially be utilized for treatment of recalcitrant mycobacterial infection especially those caused due to drug-resistant pathogens.