Charpentier, X. | Search bioRxiv

bioRxiv2018

Fluorescence-based detection of natural transformation in drug resistant Acinetobacter baumannii

Acinetobacter baumannii is a nosocomial agent with a high propensity for developing resistance to antibiotics. This ability relies on horizontal gene transfer mechanisms occurring in the Acinetobacter genus, including natural transformation. To study natural transformation in bacteria, the most prevalent method uses selection for the acquisition of an antibiotic resistance marker in a target chromosomal locus by the recipient cell. Most clinical isolates of A. baumannii are resistant to multiple antibiotics limiting the use of such selection-based method. Here we report the development of a phenotypic and selection-free method based on flow cytometry to detect transformation events in multidrug resistant (MDR) clinical A. baumannii isolates. To this end, we engineered a translational fusion between the abundant and conserved A. baumannii nucleoprotein (HU) and the superfolder green fluorescent protein (sfGFP). The new method was benchmarked against the conventional antibiotic selection-based method. Using this new method, we investigated several parameters affecting transformation efficiencies and identified conditions of transformability one hundred times higher than those previously reported. Using optimized transformation conditions, we probed natural transformation in a set of MDR clinical and non-clinical animal A. baumannii isolates. Regardless of their origin, the majority of the isolates displayed natural transformability, indicative of a conserved trait in the species. Overall, this new method and optimized protocol will greatly facilitate the study of natural transformation in the opportunistic pathogen A. baumannii.

microbiology↗

bioRxiv2017

KKL-35 Exhibits Potent Antibiotic Activity Against Legionella Species Independently Of Trans-Translation Inhibition

Trans-translation is a ribosome rescue system that is ubiquitous in bacteria. Small molecules defining a new family of oxadiazole compounds that inhibit trans-translation have been found to have broad-spectrum antibiotic activity. We sought to determine the activity of KKL-35, a potent member of the oxadiazole family, against the human pathogen Legionella pneumophila and other related species that can also cause Legionnaires disease (LD). Consistent with the essential nature of trans-translation in L. pneumophila, KKL-35 inhibits growth of all tested strains at sub-micromolar concentrations. KKL-35 is also active against other LD-causing Legionella species. KKL-35 remains equally active against L. pneumophila mutants that have evolved resistance to macrolides. KKL-35 inhibits multiplication of L. pneumophila in human macrophages at several stages of infection. No resistant mutants could be obtained, even during extended and chronic exposure. Surprisingly, KKL-35 is not synergistic with other ribosome-targeting antibiotics and does not induce the filamentation phenotype observed in cells defective for trans-translation. Importantly, KKL-35 remains active against L. pneumophila mutants expressing an alternate ribosome-rescue system and lacking tmRNA, the essential component of trans-translation. These results indicate that the antibiotic activity of KKL-35 is not related to the specific inhibition of trans-translation and its mode of action remains to be identified. In conclusion, KKL-35 is an effective antibacterial agent against the intracellular pathogen L. pneumophila and with no detectable resistance. However, further studies are needed to better understand its mechanism of action and to assess further the potential of oxadiazoles in treatment.

microbiology↗