Allosteric mechanism of aminoglycoside resistance and collateral sensitivity to chloramphenicol in Pseudomonas aeruginosa

The ribosome is the target of more than 50% of our current antibiotic arsenal, and although not frequently observed, antibiotic resistance can be acquired by mutations in ribosomal components. Here we report the molecular characterization of a 12-nucleotide deletion in the rplF gene encoding a loop in the uL6 protein of the 50S subunit from a clinical isolate of Pseudomonas aeruginosa isolated from a cystic fibrosis patient, which reveals an allosteric resistance mechanism to aminoglycosides. CryoEM structures of the PA and uL6 mutant ribosomes suggest that the deletion circumvents the action of the antibiotic by disturbing the 70S assembly and the interactions of the elongation and initiation factors with the ribosome, by modifying the electrostatic potential of the region contacting the sarcin-ricin-loop. Our data also provide evidence suggesting how the mutation enhances sensitivity to chloramphenicol, providing molecular evidence for a mechanism of collateral sensitivity.