Antibiotic resistance is a major health issue. More than 700,000 people around the world die from antibiotic-resistant bacterial infections every year—23,000 of those are in the United States (1). If we don’t find a solution, the number of deaths due to antibiotic resistance could increase to 10 million a year by 2050 (2).
Could Chemosensitizers Be the Answer to Antibiotic Resistance?
While many companies and research groups around the world are looking for new classes of antibiotics to combat antibiotic resistance, scientists from Aix-Marseille University in France believe that chemosensitizing compounds may be the answer. Chemosensitizers can alter the permeability of a bacterial cell membrane or prevent the bacteria from removing antibiotics via efflux pumps. Therefore, chemosensitizers may be able to combat antibiotic resistance by helping antibiotics cross bacterial membranes and accumulate inside bacterial cells.
A High-Throughput Assay for Chemosensitizers
To test this theory, the Aix-Marseille researchers developed a high-throughput screening platform and used it to look for chemosensitizers (3). They used a multi-drug resistant strain of Enterobacter aerogenes to screen through a library of potential chemosensitizers. Enterobacter are Gram-negative bacteria and so have two cell membranes. The double membrane is partly why Gram-negative bacteria are more resistant to antibiotics and are more likely to become multi-drug resistant than Gram-positive bacteria.
The researchers used a fluorescent dye and nitrocefin hydrolysis assay to look at whether any of their test compounds could change permeability of the E. aerogenes cell membrane or alter the efflux efficiency of the cell. All pipetting was done by a robot (Tecan Freedom EVO automated liquid handler, Tecan, France) to limit human error and prevent variation in pipetting techniques. Data was uploaded directly from the Tecan system to a custom laboratory information management system (LIMS, Modul-Bio, France).
The scientists first tested and validated their high-throughput platform with a control library of antibiotics, known membrane permeabilizers and natural and synthetic molecules. The platform found that a number of substances could chemosensitize E. aerogenes, including antimicrobial substances triclosan and chlorhexidine as well as several different antibiotic classes including polymixins, quinolones, fluoroquinolones, ß-lactams. These results validated the high-throughput assay.
Chemosensitizers Can Improve Antibiotic Efficiency
All the compounds found to change the membrane permeability or efflux efficiency of E. aerogenes were then tested to see if they could inhibit bacterial growth either alone or in combination with doxycycline. Using this method, the researchers found 24 potential chemosensitizers. Lead compounds NV731, NV845 and polymixin B nonapeptide almost completely inhibited bacterial growth when combined with doxycycline.
Conclusion
This study outlines a new high-throughput screening system to discover potential chemosensitizing agents. It also shows that several chemosensitizers can improve antibiotic efficiency in vitro. This is a very promising result, although a lot more research must be done to investigate the safety and efficacy of any potential chemosensitizers.
References
- Antibiotic Resistance and Regulation of the Gram-Negative Bacterial Outer Membrane Barrier by Host Innate Immune Molecules. mBio. 2016
- Combating Superbugs with CARB-X. Life Science Network. 2016
- Lôme et al. Multiparametric Profiling for Identification of Chemosensitizers against Gram-Negative Bacteria. Microbiol. 2018
