Comparative evaluation of five β-Lactamase inhibitors in combination with β-Lactams against multidrug-resistant Mycobacterium tuberculosis in vitro

Objective Evaluating the activity of six β-lactams in combination with different β-lactamase inhibitors to identify the most potent combination against Mycobacterium tuberculosis(MTB) in vitro. Methods A total of 105 MDR-TB strains from different regions of Henan province were included in this study.Drug susceptibility of sixβ-lactams alone or in combination with β-lactamase inhibitors was examined by broth dilution method against 105 clinical isolates.Mutations of blaC, ldt mt1 ,dacB2and ldt mt2 were analyzed by PCR and DNA sequencing. Results Out of the β-lactams used herein, tebipenem was the most effective against MDR-TB and had an MIC 90 value of 16 µg/ml.Clavulanic acid, tazobactam, and sulbactam, demonstrated the best synergy with tebipenem, resultingin an 32-fold reduction in theMIC values for 12, 5, and 20 strains, respectively. Simultaneously, these three types ofβ-lactamase inhibitors had the least impact on imipenem.Clavulanic acid caused the maximum 8-fold reduction in the MIC value of imipenem, while tazobactam and sulbactam only resulted in the maximum 4-fold reduction in the MIC value of imipenem. Besides, after the addition ofβ-lactamase inhibitors, the MICs of most β-lactam drugs were reduced more evidently in the presence of avibactamand tazobactamcompared to other β-lactamase inhibitors. In addition, 13.33% (14/105) of isolates harbored mutations in the blaC gene, with three different nucleotide substitutions: AGT333AGG 、AAC638ACCand ATC786ATT. For the strains with a Ser111Arg andAsn213Thrsubstitution inBlaC, a better synergistic effect was observed in the meropenem-clavulanate and in the meropenem-sulbactam combinationsthan that in a synonymous single nucleotide polymorphism (SNP) group. Conclusion the combination of tebipenem and relebactam shows the most potent activity against MDR-TB isolates. In addition, the Ser111Arg and Asn213Thr substitution of BlaC may be associated with increased susceptibility of MDR-TB isolates to meropenem in thepresence of clavulanate and sulbactam.