Compounds that select against the tetracycline-resistance efflux pump.

We developed a competition-based screening strategy to identify compounds that invert the selective advantage of antibiotic resistance. Using our assay, we screened over 19,000 compounds for the ability to select against the TetA tetracycline-resistance efflux pump in Escherichia coli and identified two hits, ß-thujaplicin and disulfiram. Treating a tetracycline-resistant population with ß-thujaplicin selects for loss of the resistance gene, enabling an effective second-phase treatment with doxycycline.

A Hybrid Drug Limits Resistance by Evading the Action of the Multiple Antibiotic Resistance Pathway.

Hybrid drugs are a promising strategy to address the growing problem of drug resistance, but the mechanism by which they modulate the evolution of resistance is poorly understood. Integrating high-throughput resistance measurements and genomic sequencing, we compared Escherichia coli populations evolved in a hybrid antibiotic that links ciprofloxacin and neomycin B with populations evolved in combinations of the component drugs. We find that populations evolved in the hybrid gain less resistance than those evolved in an equimolar mixture of the hybrid's components, in part because the hybrid evades resistance mediated by the multiple antibiotic resistance (mar) operon. Furthermore, we find that the ciprofloxacin moiety of the hybrid inhibits bacterial growth whereas the neomycin B moiety diminishes the effectiveness of mar activation. More generally, comparing the phenotypic and genotypic paths to resistance across different drug treatments can pinpoint unique properties of new compounds that limit the emergence of resistance.

Distinguishing between attributional and mnemonic sources of familiarity: the case of positive emotion bias.

Does familiarity arise from direct access to memory representations (a mnemonic account) or from inferences and diagnostic cues (an attributional account)? These theoretically distinct explanations can be difficult to distinguish in practice, as is shown by the positivity effect, the increase in feelings of familiarity that accompanies positive emotion. Experiment 1 manipulated mnemonic and attributional sources of positivity via word valence and physical expressions of emotion, respectively. Both sources influenced the tendency to call items old, but receiver-operating characteristic analysis revealed a change in accuracy only with the mnemonic source. To further contrast the mnemonic and attributional accounts, Experiment 2 varied the ratio of positive to neutral words. A higher proportion of positive words exaggerated the pattern of increased old judgments and decreased accuracy for positive words, relative to neutral ones, consistent with the mnemonic account but inconsistent with the attributional account.

Ubiquitous selection for mecA in community-associated MRSA across diverse chemical environments.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is threatening public health as it spreads worldwide across diverse environments. Its genetic hallmark, the mecA gene, confers resistance to many ß-lactam antibiotics. Here, we show that, in addition, mecA provides a broad selective advantage across diverse chemical environments. Competing fluorescently labelled wild-type and mecA-deleted CA-MRSA USA400 strains across ~57,000 compounds supplemented with subinhibitory levels of the ß-lactam drug cefoxitin, we find that mecA provides a widespread advantage across ß-lactam and non ß-lactam antibiotics, non-antibiotic drugs and even diverse natural and synthetic compounds. This advantage depends on the presence of cefoxitin and is strongly associated with the compounds' physicochemical properties, suggesting that it may be mediated by differential compounds permeability into the cell. Indeed, mecA protects the bacteria against increased cell-envelope permeability under subinhibitory cefoxitin treatment. Our findings suggest that CA-MRSA success might be driven by a cell-envelope mediated selective advantage across diverse chemical compounds.

Multidrug evolutionary strategies to reverse antibiotic resistance.

Antibiotic treatment has two conflicting effects: the desired, immediate effect of inhibiting bacterial growth and the undesired, long-term effect of promoting the evolution of resistance. Although these contrasting outcomes seem inextricably linked, recent work has revealed several ways by which antibiotics can be combined to inhibit bacterial growth while, counterintuitively, selecting against resistant mutants. Decoupling treatment efficacy from the risk of resistance can be achieved by exploiting specific interactions between drugs, and the ways in which resistance mutations to a given drug can modulate these interactions or increase the sensitivity of the bacteria to other compounds. Although their practical application requires much further development and validation, and relies on advances in genomic diagnostics, these discoveries suggest novel paradigms that may restrict or even reverse the evolution of resistance.

ABC transporters required for export of wall teichoic acids do not discriminate between different main chain polymers.

The cell envelopes of Gram-positive bacteria comprise two major constituents, peptidoglycan and teichoic acids. Wall teichoic acids (WTAs) are anionic glycophosphate polymers that play important roles in bacterial cell growth, division, and pathogenesis. They are synthesized intracellularly and exported by an ABC transporter to the cell surface, where they are covalently attached to peptidoglycan. We address here the substrate specificity of WTA transporters by substituting the Bacillus subtilis homologue, TagGH(Bs), with the Staphylococcus aureus homologue, TarGH(Sa). These transporters export structurally different substrates in their indigenous organisms, but we show that TarGH(Sa) can substitute for the B. subtilis transporter. Hence, substrate specificity does not depend on the WTA main chain polymer structure but may be determined by the conserved diphospholipid-linked disaccharide portion of the WTA precursor. We also show that the complemented B. subtilis strain becomes susceptible to a S. aureus-specific antibiotic, demonstrating that the S. aureus WTA transporter is the sole target of this compound.