Beta-lactam combination treatment overcomes rifampicin resistance in Mycobacterium tuberculosis

The significant global impact of tuberculosis (TB) on human health is exacerbated by the increasing prevalence of multi-drug resistant tuberculosis (MDR-TB) and the challenges of novel drug discovery for the treatment of drug-susceptible and drug-resistant strains of M. tuberculosis. Rifampicin is a key first-line TB drug and rifampicin resistance is a major obstacle to treating MDR-TB. Utilising existing antimicrobial drugs to supplement combination therapy and overcome rifampicin resistance is a promising solution due to their widespread availability and proven clinical safety profile. Therefore, this study aimed to explore the feasibility of using beta-lactam/beta-lactamase inhibitor combinations with rifampicin to inhibit the growth of multidrug-resistant M. tuberculosis. Based on inhibitory concentration (IC), oral bioavailability, pricing, commercial availability, five beta-lactams and the beta-lactamase inhibitor, clavulanate, were selected for testing. These were combined with rifampicin for in vitro testing against Mycobacterium tuberculosis H37Rv. Resazurin assays and colony forming unit (CFU) enumeration were used to quantify drug efficacy, Chou-Talalay calculations were performed to identify drug synergy and Chou-Martin calculations were performed to quantify drug dose reduction index (DRI). The combination of tebipenem-clavulanate/rifampicin and cephradine-clavulanate/rifampicin were found to be synergistic and highly effective against clinical isolates of MDR-TB, overcoming rifampicin resistance in vitro. Beta-lactam synergy may provide viable combination therapies with rifampicin to address the issue of drug resistance in TB.