Phase variation inMycobacterium tuberculosis glpKproduces transiently heritable drug tolerance

Abstract

The length and complexity of tuberculosis (TB) therapy, as well as the propensity ofMycobacterium tuberculosisto develop drug resistance, are major barriers to global TB control efforts.M. tuberculosisis known to have the ability to enter into a drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a mechanism of genetically encoded but rapidly reversible drug tolerance inM. tuberculosiscaused by transient frameshift mutations in a homopolymeric tract (HT) of 7 cytosines (7C) in theglpKgene. Inactivating frameshift mutations associated with the 7C HT inglpKproduce small colonies that exhibit heritable multidrug increases in minimal inhibitory concentrations and decreases in drug-dependent killing; however, reversion back to a fully drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the sameglpKHT region. These reversible frameshift mutations in the 7C HT ofM. tuberculosis glpKoccur in clinical isolates, accumulate inM. tuberculosis-infected mice with further accumulation during drug treatment, and exhibit a reversible transcriptional profile including induction ofdosRandsigHand repression ofkstRregulons, similar to that observed in other in vitro models ofM. tuberculosistolerance. These results suggest that GlpK phase variation may contribute to drug tolerance, treatment failure, and relapse in human TB. Drugs effective against phase-variantM. tuberculosismay hasten TB treatment and improve cure rates.