A Whole-Cell Screen Identifies Small Bioactives That Synergize with Polymyxin and Exhibit Antimicrobial Activities against Multidrug-Resistant Bacteria

Abstract

The threat of diminished antibiotic discovery has global health care in crisis. In the United States, it is estimated each year that over 2 million bacterial infections are resistant to first-line antibiotic treatments and cost in excess of 20 billion dollars. Many of these cases result from infection with the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species), which are multidrug-resistant bacteria that often cause community- and hospital-acquired infections in both healthy and immunocompromised patients. Physicians have turned to last-resort antibiotics like polymyxins to tackle these pathogens, and as a consequence, polymyxin resistance has emerged and is spreading. Barring the discovery of new antibiotics, another route to successfully mitigate polymyxin resistance is to identify compounds that can complement the existing arsenal of antibiotics. We recently designed and performed a large-scale robotic screen to identify 43 bioactive compounds that act synergistically with polymyxin B to inhibit the growth of polymyxin-resistant Escherichia coli. Of these 43 compounds, 5 lead compounds were identified and characterized using various Gram-negative bacterial organisms to better assess their synergistic activity with polymyxin. Several of these compounds reduce polymyxin to an MIC of <2 μg/ml against polymyxin-resistant and polymyxin-heteroresistant Gram-negative pathogens. Likewise, four of these compounds exhibit antimicrobial activity against Gram-positive bacteria, one of which rapidly eradicated methicillin-resistant Staphylococcus aureus. We present multiple first-generation (i.e., not yet optimized) compounds that warrant further investigation and optimization, since they can act both synergistically with polymyxin and also as lone antimicrobials for combating ESKAPE pathogens.

2‐Aminobenzothiazoles Inhibit Virulence Gene Expression and Block Polymyxin Resistance in Salmonella enterica

“…This mechanism of resistance to CAMPs is conserved throughout the family Enterobacteriaceae, which includes multiple antibiotic‐resistant pathogens in addition to Salmonella [11] . Therefore, targeting bacterial resistance to CAMPs has potential application to a wide variety of antibiotic‐resistant bacteria [12] …”

“…[11] Therefore, targeting bacterial resistance to CAMPs has potential application to a wide variety of antibiotic-resistant bacteria. [12] LPS modifications that confer resistance to CAMPs are regulated by two-component signaling systems in Salmonella and other enterobacteria. [9,11,13] These signaling systems comprise a histidine kinase (HK) embedded in the cytoplasmic membrane and a response regulator in the cytoplasm.…”

A New Surface Charge Neutralizing Nano-Adjuvant to Potentiate Polymyxins in Killing Mcr-1 Mediated Drug-Resistant Escherichia coli

“…It has been known that polymyxin resistance principally arises from structural remodeling of lipid A anchored on the bacterial surface [ 7 ]. In Mcr-1 strains, ArnT and EptA modifications were observed [ 25 ]. We questioned whether either of ArnT or EptA modification is required for the synergistic action of NZB to PolB.…”

“…E. coli is generally known to have negative charge on its surface due to the negatively charged lipid A on the LPS component [ 7 , 25 ]. However, Mcr-1 modification changes the charge of E. coli cells from negative to marginally positive owing to the lipid A modifications by ArnT and EptA [ 7 , 25 ]. As NZB is a negatively charged nanocomposite, it is expected that charge neutralization between NZB and Mcr-1 modified E. coli cells makes cells more prone to attack by a positively charged PolB.…”

“…Therefore, the aim of this study is to find a nano-adjuvant to potentiate polymyxins in killing Mcr-1 mediated drug-resistant Escherichia coli . It has been known that Mcr-1 action modified the bacterial surface charge to be more positive compared to non-Mcr-1 expressing bacteria [ 25 ]. Therefore, we hypothesized that nanoparticles (NPs) of high specificity to Gram-negative bacteria with positive charge neutralizing activity will specifically be used as potential targeting materials for Mcr-1 associated polymyxin-resistant E. coli cells.…”