Differential activity profiles of translation inhibitors in whole-cell and cell-free approaches

Evaluation of the activity profiles of standard prokaryotic translation inhibitors with different physicochemical properties under whole-cell and cell-free conditions.

The minimal inhibitory concentration values (cell-free/whole-cell microg ml(-1)) for three aminoglycosides (neomycin, 0.01/6.92; paromomycin, 0.7/1.96; streptomycin 1.45/1.57), three macrolides (erythromycin, 1.53/56.9; josamycin, 1.61/87.7; oleandomycin, 5.12/565.9), chloramphenicol (11.9/3.04), and two tetracyclines (tetracycline hydrochloride, not determined/0.63; minocycline hydrochloride, 2.53/1.09), towards Escherichia coli A19 cells were determined with a microtitre plate-based broth dilution method and compared with values determined in a coupled transcription/translation system based on a S30 extract of the same E. coli strain (cell-free) for the production of the green fluorescent protein.

The analysed prokaryotic translation inhibitors showed substance-specific activity profiles under cell-free vs whole-cell conditions that are explainable by the physicochemical properties of the molecules.

This study shows the advantages and limits of cell- free transcription/translation (CFTT) experiments for the discovery of novel antimicrobials. The main advantage is the direct access of the target structures (ribosomes) for the inhibitors, and our results provide an estimation of the concentration necessary to detect new agents. The main limitations are that the inhibitory properties of different agents in CFTT experiments do not necessarily reflect their growth inhibition activity in cell cultures.