Role of AcrAB-TolC and Its Components in Influx-Efflux Dynamics of QAC Drugs in Escherichia coli Revealed Using SHG Spectroscopy.

Multidrug efflux pumps, especially those belonging to the class of resistance-nodulation-division (RND), are the key contributors to the rapidly growing multidrug resistance in Gram-negative bacteria. Understanding the role of efflux pumps in real-time drug transport dynamics across the complex dual-cell membrane envelope of Gram-negative bacteria is thus crucial for developing efficient antibiotics against them. Here, we employ second harmonic generation-based nonlinear spectroscopy to study the role of the tripartite efflux pump and its individual components. We systematically investigate the effect of periplasmic adaptor protein AcrA, inner membrane transporter protein AcrB, and outer membrane channel TolC on the overall drug transport in live Acr-type Escherichia coli and its mutant strain cells. Our results reveal that when one of its components is missing, the tripartite AcrAB-TolC efflux pump machinery in Escherichia coli can effectively function as a bipartite system, a fact that has never been demonstrated in live Gram-negative bacteria.