CarO, an Acinetobacter baumannii outer membrane protein involved in carbapenem resistance, is essential for l-ornithine uptake

We previously associated the emergence of carbapenem resistance in Acinetobacter baumannii with the loss of an outer membrane (OM) protein designated CarO. CarO was found essential for l-ornithine uptake: CarO-deficient strains were specifically impaired to grow only on l-ornithine, and failed to incorporate l-[14C] ornithine from the medium. l-arginine, and histidine and lysine to a lower extent, could effectively compete for l-[14C] ornithine uptake. l-ornithine also reduced A. baumannii sensitivity to imipenem, suggesting that both compounds compete for uptake. The overall results indicate that CarO participates in the selective uptake of l-ornithine, carbapenems, and other basic amino acids in A. baumannii.