Tuesday, 2 July 2019

The powers of bacteria visualized in real time

The global spread of antibiotic resistance is a major public health issue and a priority for international microbiology research. In a new paper, researchers report on filming the process of antibiotic resistance acquisition in real time, discovering a key but unexpected player in its maintenance and spread within bacterial populations.



In his paper to be published in the journal Science, Christian Lesterlin, Inserm researcher at Lyon's "Molecular Microbiology and Structural Biochemistry" laboratory (CNRS/Université Claude Bernard Lyon 1), and his team were able to film the process of antibiotic resistance acquisition in real time, discovering a key but unexpected player in its maintenance and spread within bacterial populations.

The researchers chose to study the acquisition of Escherichia coli resistance to tetracycline, a commonly used antibiotic, by placing a bacterium that is sensitive to tetracycline in the presence of one that is resistant. Previous studies have shown that such resistance involves the ability of the bacterium to expel the antibiotic before it can exert its destructive effect using "efflux pumps" found on its membrane. These specific efflux pumps are able to eject the antimicrobial molecules from the bacteria, thereby conferring on them a certain level of resistance.

In this experiment, the transmission of the DNA from one specific "efflux pump" -- the TetA pump -- was observed between a resistant bacterium and a sensitive bacterium using fluorescent marking. Thanks to live-cell microscopy, the researchers just had to track the progression of the fluorescence to see how the DNA of the "pump" migrated from one bacterium to another and how it was expressed in the recipient bacterium.

The researchers revealed that in just 1 to 2 hours, the single-stranded DNA fragment of the efflux pump was transformed into double-stranded DNA and then translated into functional protein, thereby conferring the tetracycline resistance on the recipient bacterium.

In their video, the transfer of DNA from the donor bacteria (green) to the recipient bacteria (red) is revealed by the appearance of red localization foci. The rapid expression of the newly acquired genes is revealed by the production of green fluorescence in the recipient bacteria.

See: Sophie Nolivos, Julien Cayron, Annick Dedieu, Adeline Page, Frederic Delolme, Christian Lesterlin. Role of AcrAB-TolC multidrug efflux pump in drug-resistance acquisition by plasmid transfer. Science, 2019; 364 (6442): 778 DOI: 10.1126/science.aav6390

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology

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