The central role of the Escherichia coli effluxome in bacterial physiology and development of antibiotic resistance.

Multidrug Transporters (MDTs) are major contributors to the acquisition and maintenance of Antimicrobial Resistance (AMR), a growing public health threat of broad concern. Despite the large number of MDTs, the overwhelming majority of the studies performed thus far in Gram-negative bacteria emphasize the supremacy of the AcrAB-TolC complex. To unveil the potential role of other MDTs we studied the behavior of a nil AcrB Escherichia coli strain when challenged with chloramphenicol, a bacteriostatic antibiotic. We found that such a strain developed an extremely high-level of resistance to chloramphenicol, cross-resistance to quinolones and erythromycin and displayed high levels of expression of the single component MFS transporter MdfA and multiple TolC-dependent transporters. The results suggest that the high versatility of the whole ensemble of transporters, the bacterial Effluxome, is an essential part of a strategy of survival in ever-changing, at times noxious, environments.

This versatility is made possible by dozens of transporters that labor together, their interaction and crosstalk dictated by thermodynamics and regulated when needs arise. Random gene disruption through transposon mutagenesis in the strains developed in our lab allows identification of novel players that contribute to the high-level resistance displayed.

The concept of a functional Effluxome presents an alternative to the existing paradigms in the field and provides novel targets for the search for inhibitors of transporters as adjuvants of existing antibiotics.