Mycobacterium tuberculosis (Mtb) is the leading infectious cause of death. Synthesis of lipids critical for Mtb’s cell wall and virulence depends on phosphopantetheinyl transferase (PptT), an enzyme that transfers 4’-phosphopantetheine (Ppt) from coenzyme A to diverse acyl carrier proteins (ACPs). We identified a compound that kills Mtb by binding and partially inhibiting PptT. Killing of Mtb by the compound is potentiated by another enzyme encoded in the same operon, Ppt hydrolase (PptH), that undoes the PptT reaction. Thus, loss of function mutants of PptH displayed antimicrobial resistance. Our PptT-inhibitor co-crystal structure may aid further development of anti-mycobacterial agents against this long-sought target. The opposing reactions of PptT and PptH uncover a regulatory pathway in CoA physiology.
Measurement of the reduction in CFU in sputum of patients with TB up to 2 weeks after the initiation of treatment is the gateway test for a new TB treatment. Reports have suggested that CFU assays fail to detect the majority of viable M. tuberculosis cells in sputum samples from the majority of patients when the number of M. tuberculosis is estimated by limiting dilution (LD). In an effort to avoid potential methodologic confounders, we applied a modified version of the LD assay in a study of a geographically distinct population. We confirmed that differentially detectable (DD) M. tuberculosis is often found before treatment, albeit at lower proportionate levels than in earlier reports. Strikingly, the prevalence and proportionate representation of DD M. tuberculosis increased during standard treatment. Sublethal exposure to certain antibiotics may help generate DD M. tuberculosis cells or enrich their representation among the surviving bacteria, and this may contribute to the need for prolonged treatment with those agents in order to achieve durable cures.
The historical view of β-lactams as ineffective antimycobacterials has given way to growing interest in the activity of this class against Mycobacterium tuberculosis (Mtb) in the presence of a β-lactamase inhibitor. However, most antimycobacterial βlactams kill Mtb only or best when the bacilli are replicating. Here, a screen of 1904 β-lactams led to the identification of cephalosporins substituted with a pyrithione moiety at C3′ that are active against Mtb under both replicating and nonreplicating conditions, neither activity requiring a β-lactamase inhibitor. Studies showed that activity against nonreplicating Mtb required the in situ release of the pyrithione, independent of the known class A β-lactamase, BlaC. In contrast, replicating Mtb could be killed both by released pyrithione and by the parent β-lactam. Thus, the antimycobacterial activity of pyrithionecontaining cephalosporins arises from two mechanisms that kill mycobacteria in different metabolic states.
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