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Updated: May 17, 2026
Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes
Published on: March 2, 2020
Physico-chemical factors affect chloramphenicol efflux and EmhABC efflux pump expression in Pseudomonas fluorescens
Abigail Adebusuyi1, Julia Foght
1Department of Biological Sciences, CW405 Biological Sciences Center, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. adebusuy@ualberta.ca
Abstract:
Protein synthesis inhibitors such as chloramphenicol and tetracycline may be inducers of efflux pumps such as MexY in Pseudomonas aeruginosa, complicating their use for the treatment of bacterial infections. We previously determined that chloramphenicol, a substrate of the EmhABC efflux pump in Pseudomonas fluorescens cLP6a, did not induce emhABC expression. In this study, we determined the effect of physico-chemical factors on chloramphenicol efflux by EmhABC, and the expression of emhABC. Efflux assays measuring accumulation of (14)C-chloramphenicol in cell pellets showed that chloramphenicol efflux is dependent on growth temperature, pH and concentration of Mg(2+). These physico-chemical factors modulated the efflux of chloramphenicol by 26 to >50%. All conditions tested that decreased the efflux of chloramphenicol unexpectedly induced transcription of emhABC efflux genes. EmhABC activity also effectively suppressed the deleterious effect of chloramphenicol on the cell membrane of strain cLP6a, which may explain why chloramphenicol is not an inducer of emhABC. Our results suggest that the detrimental effect of an antibiotic on cell membrane integrity and fatty acid composition may be the signal that induces emhABC expression, and that inducers of other bacterial efflux pumps may include environmental factors rather than their substrates per se.
Insights
Environmental factors, not substrates, may induce bacterial efflux pumps like EmhABC. Conditions decreasing chloramphenicol efflux unexpectedly increased emhABC gene transcription in Pseudomonas fluorescens.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Protein synthesis inhibitors can induce bacterial efflux pumps, complicating antibiotic treatment.
- Chloramphenicol, an antibiotic, is a substrate for the EmhABC efflux pump in Pseudomonas fluorescens but does not induce its expression.
Purpose of the Study:
- To investigate the influence of physico-chemical factors on chloramphenicol efflux mediated by EmhABC.
- To examine the impact of these factors on the expression of emhABC genes.
Main Methods:
- Utilized efflux assays with (14)C-chloramphenicol to measure accumulation in cell pellets.
- Analyzed the effects of varying growth temperature, pH, and Mg(2+) concentration on efflux and gene expression.
Main Results:
- Chloramphenicol efflux by EmhABC was significantly influenced by growth temperature, pH, and Mg(2+) concentration (26% to >50% modulation).
- Conditions that reduced chloramphenicol efflux paradoxically led to increased emhABC gene transcription.
- EmhABC activity mitigated the detrimental effects of chloramphenicol on the bacterial cell membrane.
Conclusions:
- Antibiotic-induced cell membrane damage may be the primary signal for emhABC efflux gene expression.
- Environmental factors, rather than antibiotic substrates themselves, are likely inducers for many bacterial efflux pumps.
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