Resistance to Ceftazidime/Avibactam plus Meropenem/Vaborbactam When Both Are Used Together Is Achieved in Four Steps in Metallo-ß-Lactamase-Negative Klebsiella pneumoniae.

Serine ß-lactamases are dominant causes of ß-lactam resistance in Klebsiella pneumoniae isolates. Recently, this has driven clinical deployment of the ß-lactam-ß-lactamase inhibitor pairs ceftazidime/avibactam and meropenem/vaborbactam. We show that four steps, i.e., ompK36 and ramR mutation plus carriage of OXA-232 and KPC-3-D178Y variant ß-lactamases, confer ceftazidime/avibactam and meropenem/vaborbactam resistance when both pairs are used together. These findings have implications for decision making about sequential and combinatorial use of these ß-lactam-ß-lactamase inhibitor pairs to treat K. pneumoniae infections.

The distinct translational landscapes of gram-negative Salmonella and gram-positive Listeria.

Translational control in pathogenic bacteria is fundamental to gene expression and affects virulence and other infection phenotypes. We used an enhanced ribosome profiling protocol coupled with parallel transcriptomics to capture accurately the global translatome of two evolutionarily distant pathogenic bacteria-the Gram-negative bacterium Salmonella and the Gram-positive bacterium Listeria. We find that the two bacteria use different mechanisms to translationally regulate protein synthesis. In Salmonella, in addition to the expected correlation between translational efficiency and cis-regulatory features such as Shine-Dalgarno (SD) strength and RNA secondary structure around the initiation codon, our data reveal an effect of the 2nd and 3rd codons, where the presence of tandem lysine codons (AAA-AAA) enhances translation in both Salmonella and E. coli. Strikingly, none of these features are seen in efficiently translated Listeria transcripts. Instead, approximately 20% of efficiently translated Listeria genes exhibit 70 S footprints seven nt upstream of the authentic start codon, suggesting that these genes may be subject to a novel translational initiation mechanism. Our results show that SD strength is not a direct hallmark of translational efficiency in all bacteria. Instead, Listeria has evolved additional mechanisms to control gene expression level that are distinct from those utilised by Salmonella and E. coli.