An Assay to Measure the Accumulation of a Fluorescent Antibiotic Probe in Bacterial Cells

In This Article

Abstract

Source: Stone, M. R. L., et al. Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes. J. Vis. Exp. (2020).

This video demonstrates an assay to measure the accumulation of a fluorescent antibiotic probe in bacterial cells. Exposure to an efflux pump inhibitor disrupts the transmembrane proton gradient in bacterial cells, upon which a fluorophore-conjugated antibiotic is added. Inhibition of efflux pumps due to the disrupted proton gradient causes accumulation of the antibiotic inside the bacteria. Bacterial cells are lysed, and the fluorescence intensity is measured to confirm antibiotic accumulation.

Protocol

1. Evaluation of Antimicrobial Activity

NOTE: All work involving bacteria should be carried out under sterile conditions to avoid contamination of either the assay or the laboratory. All media should be autoclaved before use, and plasticware and equipment such as pipettes must be kept sterile. It is recommended that work be done in a biocontainment hood (type 2).

Streak glycerol stocks of bacterial strains appropriate for the antibiotic scaffold onto lysogeny broth agar (LB, prepared per manufacturer's instructions), and grow overnight at 37 °C.
NOTE: The choice of b....

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Results

Table 1. Antibiotic activities of fluorescent antibiotic probes based on ciprofloxacin, trimethoprim, and linezolid against appropriate clinically relevant bacterial strains, as measured by broth microdilution MIC assays. In most cases, the probes lost some activity compared to the parent drug, but retained some measurable antibiotic potency (sufficient to be useful in further studies).