Rapid cytolysis of Mycobacterium tuberculosis by faropenem, an orally bioavailable ß-lactam antibiotic.

Recent clinical studies indicate that meropenem, a ß-lactam antibiotic, is a promising candidate for therapy of drug-resistant tuberculosis. However, meropenem is chemically unstable, requires frequent intravenous injection, and must be combined with a ß-lactamase inhibitor (clavulanate) for optimal activity. Here, we report that faropenem, a stable and orally bioavailable ß-lactam, efficiently kills Mycobacterium tuberculosis even in the absence of clavulanate. The target enzymes, L,D-transpeptidases, were inactivated 6- to 22-fold more efficiently by faropenem than by meropenem. Using a real-time assay based on quantitative time-lapse microscopy and microfluidics, we demonstrate the superiority of faropenem to the frontline antituberculosis drug isoniazid in its ability to induce the rapid cytolysis of single cells. Faropenem also showed superior activity against a cryptic subpopulation of nongrowing but metabolically active cells, which may correspond to the viable but nonculturable forms believed to be responsible for relapses following prolonged chemotherapy. These results identify faropenem to be a potential candidate for alternative therapy of drug-resistant tuberculosis.

Characterization of broad-spectrum Mycobacterium abscessus class A ß-lactamase.

OBJECTIVES: Imipenem and cefoxitin are used to treat Mycobacterium abscessus infections and have moderate activity against this fast-growing mycobacterium (MIC50 of 16 and 32 mg/L, respectively). M. abscessus is highly resistant to most other ß-lactams, although the underlying mechanisms have not been explored. Here, we characterized M. abscessus class A ß-lactamase (Bla(Mab)) and investigated its role in ß-lactam resistance. METHODS: Hydrolysis kinetic parameters of purified Bla(Mab) were determined by spectrophotometry for various ß-lactams and compared with those of related BlaC from Mycobacterium tuberculosis. MICs of ß-lactams were determined for M. abscessus CIP104536 and for Escherichia coli producing Bla(Mab) and BlaC. RESULTS: Bla(Mab) had a broad hydrolysis spectrum, similar to that of BlaC, but with overall higher catalytic efficiencies, except for cefoxitin. As expected from its in vivo efficacy, cefoxitin was very slowly hydrolysed by Bla(Mab) (k(cat)/K(m) = 6.7 M(-1) s(-1)). Bla(Mab) hydrolysed imipenem more efficiently (k(cat)/K(m) = 3.0 × 10(4) M(-1) s(-1)), indicating that the in vivo activity of this drug might be improved by combination with a ß-lactamase inhibitor. ß-Lactamase inhibitors clavulanate, tazobactam and sulbactam did not inhibit Bla(Mab). This enzyme efficiently hydrolysed clavulanate, in contrast to BlaC, which is irreversibly acylated by this inhibitor. Bla(Mab) and BlaC were functional in E. coli and the resistance profiles mediated by these enzymes were in agreement with the kinetic parameters. CONCLUSIONS: M. abscessus produces a clavulanate-insensitive broad-spectrum ß-lactamase that limits the in vivo efficacy of ß-lactams.