Enhanced Efflux Activity Facilitates Drug Tolerance in Dormant Bacterial Cells

Pu, Y., et al. Molecular cell 62, 284-294 (2016)

Speaker: Tsai-Yu Wu (吳彩瑜)                                     Time: 15:00~16:00, Sep. 21, 2016

Commentator: Dr. I-Hsiu Huang (黃一修老師)           Place: Room 601

Abstract

Gene expression stochasticity led to cell substantial phenotypic variation. Such heterogeneity arose from transcription and translation level, and resulted in cell-to-cell variations. In order to survival under rapid changing environment, bacteria undergo a ‘bet-hedging’ mechanism¹. This mechanism enabled bacteria population maximized its survival chance when facing the fluctuating environmental condition. Previous studied have investigated that a small group of bacterial cells may escape the attack from antibiotics without genetic changing, and these cells were called persisters². The existence of persisters is believed to increase the severity of many diseases, so developing an effective treatment is very important. Previously, persister formation was considered mainly associated with cell dormancy³. These theories explained that the lethal effects of persisterswere due to the extremely slow metabolic and proliferation rate. However, a simple question whether antibiotic effectively enter and accumulated in persister cells to exert their effects remained unclear. In this study, the authors combined in vivo fluorescent imaging and next-generation sequencing to demonstrate the mechanisms for persister formation. The in vivo fluorescence test showed that antibiotic accumulated at lower level in persisters, and the authors further explored less drug accumulation was due to enhanced efflux activity. In addition, many multi-drug efflux genes, especially the central component TolC, showed high expression level in persisters. Combination of time-lapse imaging and mutagenesis studies also showed a positive relation between tolC expression and bacterial persistence. Moreover, the authors tested a therapeutic strategy and explored that antibiotics combined with efflux pump inhibiors could efficiently eradicate persisters. These results revealed that in addition to a passive defense via dormancy, persister cells utilized a positive defense against antibiotic accumulation by enhanced efflux activity and survived from antibiotics attack.

References

1.         Raj, A. & van Oudenaarden, A. Nature, nurture, or chance: stochastic gene expression and its consequences. Cell 135, 216-226 (2008).

2.         Wood, T.K., Knabel, S.J. & Kwan, B.W. Bacterial persister cell formation and dormancy. Applied and environmental microbiology 79, 7116-7121 (2013).

3.         Rotem, E., et al. Regulation of phenotypic variability by a threshold-based mechanism underlies bacterial persistence. Proceedings of the National Academy of Sciences of the United States of America 107, 12541-12546 (2010).