In vitro activity of new combinations of β-lactam and β-lactamase inhibitors against the Mycobacterium tuberculosis complex

Abstract

As meropenem-clavulanic acid is recommended for the treatment of drug-resistant tuberculosis, the repurposing of new carbapenem combinations may provide new treatment options, including oral alternatives. Therefore, we studied the in vitro activities of meropenem-vaborbactam, meropenem-clavulanic acid, and tebipenem-clavulanic acid. One hundred nine Mycobacterium tuberculosis complex (MTBC) clinical isolates were tested, of which 69 were pan-susceptible and the remaining pyrazinamide- or multidrug-resistant. Broth microdilution MICs were determined using the EUCAST reference method. Meropenem and tebipenem were tested individually and in combination with vaborbactam 8 mg/L and clavulanic-acid 2 and 4 mg/L, respectively. Whole-genome sequencing was performed to explore resistance mechanisms. Clavulanic acid lowered the modal tebipenem MIC approximately 16-fold (from 16 to 1 mg/L). The modal meropenem MIC was reduced twofold by vaborbactam compared with an approximately eightfold decrease by clavulanic acid. The only previously described high-confidence carbapenem resistance mutation, crfA T62A, was shared by a subgroup of lineage 4.3.4.1 isolates and did not correlate with elevated MICs. The presence of a β-lactamase inhibitor reduced the MTBC MICs of tebipenem and meropenem. The resulting MIC distribution was lowest for the orally available drugs tebipenem-clavulanic acid. Whether this in vitro activity translates to similar or greater clinical efficacy of tebipenem-clavulanic acid compared with the currently WHO-endorsed meropenem-clavulanic acid requires clinical studies. IMPORTANCE Repurposing of already approved antibiotics, such as β-lactams in combination with β-lactamase inhibitors, may provide new treatment alternatives for drug-resistant tuberculosis. Meropenem-clavulanic acid was more active in vitro compared to meropenem-vaborbactam. Notably, tebipenem-clavulanic acid showed even better activity, raising the potential of an all-oral treatment option. Clinical data are needed to investigate whether the better in vitro activity of tebipenem-clavulanic acid correlates with greater clinical efficacy compared with the currently WHO-endorsed meropenem-clavulanic acid.

Keywords: BlaC; clavulanic acid; drug resistance mechanisms; meropenem; minimum inhibitory concentrations; tebipenem; vaborbactam; β-lactamases; β-lactams.

Fig 1

MICs for tebipenem alone or in combination with either 2 or 4 mg/L clavulanic acid. (a) 109 clinical isolates were tested once, and unusually low or high MICs are detailed in Table 1. (b) The H37Rv control strain was included in each batch of clinical isolates. CLA, clavulanic acid; TBM, tebipenem.

Fig 2

MICs for meropenem alone or in combination with either 8 mg/L vaborbactam or 2 mg/L clavulanic acid. (a) 109 clinical isolates were tested once, and unusually low or high MICs are detailed in Table 1. (b) The H37Rv control strain was included in each batch of clinical isolates. CLA, clavulanic acid; MEM, meropenem; VAB, vaborbactam.

Fig 3

Phylogenetic relationship of crfA T62A and its correlation with MICs. Based on a phylogenetically diverse reference collection encompassing all major MTBC lineages, crfA T62A was shared by a subgroup of clinical lineage 4.3.4.1 isolates. The MICs of the two clinical lineage 4.3.4.1 isolates with crfA T62A and two clinical wild-type isolates (one from lineage 4.3.4.1 and the other from 4.3.4.2), which are highlighted in red, were measured. crfA T62A was found not to affect the MIC of any carbapenem (MICs presented in Table 2).