In Vitro Activity of β-Lactams in Combination with β-Lactamase Inhibitors against Mycobacterium tuberculosis Clinical Isolates

Objectives. Evaluating the activity of nineteen beta-lactams in combination with different beta-lactamase inhibitors to determine the most potent combination against Mycobacterium tuberculosis (MTB) in vitro. Methods. Drug activity was examined by drug susceptibility test with 122 clinical isolates from China. Mutations of blaC and drug targets ldt(Mt1), ldt(Mt2), dacB2, and crfA were analyzed by nucleotide sequencing. Results. Tebipenem (TBM) in combination with clavulanate (CLA) exhibited the highest anti-TB activity. The MIC of beta-lactam antibiotics was reduced most evidently in the presence of CLA, compared to avibactam (AVI) and sulbactam (SUB). Eight polymorphism sites were identified in blaC, which were not associated with beta-lactams resistance. Interestingly, one strain carrying G514A mutation in blaC was highly susceptible to beta-lactams regardless of the presence of inhibitors. The transpeptidase encoding genes, ldt(Mt1), ldt(Mt2), and dacB2, harboured three mutations, two mutations, and one mutation, respectively, but no correlation was found between these mutations and drug resistance. Conclusion, the activity of beta-lactams against MTB and different synergetic effect of beta-lactamase inhibitors were indicated. TBM/CLA exhibited the most activity and has a great prospect in developing novel anti-TB regimen; however, further clinical research is warranted. Moreover, the resistance to the beta-lactam antibiotics might not be conferred by single target mutation in MTB and requires further studies.