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

Abstract

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 L-ornithine uptake: CarO-deficient strains were specifically impaired to grow only on L L-ornithine, and failed to incorporate L L-[ 14 C] ornithine from the medium. L L-arginine, and histidine and lysine to a lower extent, could effectively compete for L L-[ 14 C] ornithine uptake. L 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 L-ornithine, carbapenems, and other basic amino acids in A. baumannii.

Horizontal Gene Transfer and Assortative Recombination within the Acinetobacter baumannii Clinical Population Provide Genetic Diversity at the Single carO Gene, Encoding a Major Outer Membrane Protein Channel

“…We also demonstrated that CarO is involved in the OM permeation of L-ornithine, a basic amino acid that displays structural similarity with carbapenems (31). These observations led us to hypothesize that CarO may allow carbapenem influx across the A. baumannii OM and that strains in which the carO gene was inactivated could have been selected under carbapenem pressure (29,31).…”

“…We also demonstrated that CarO is involved in the OM permeation of L-ornithine, a basic amino acid that displays structural similarity with carbapenems (31). These observations led us to hypothesize that CarO may allow carbapenem influx across the A. baumannii OM and that strains in which the carO gene was inactivated could have been selected under carbapenem pressure (29,31). However, carO was not always interrupted in all of our clonally related carbapenem-resistant A. baumannii isolates (29), indicating that a mechanism(s) other than carO disruptions can also account for the reduced carbapenem susceptibility phenotype.…”

“…Determination of the relative contents of CarO variants in A. baumannii OM fractions. The relative contents of CarO variants in the OM of the A. baumannii strains analyzed here were determined by following procedures described previously (29,31). In short, CarO and Omp40 protein bands were excised from Coomassie blue-stained gels and separately incubated in 1 ml of 25% (vol/vol) pyridine overnight.…”

“…4A and B) were done at 37°C under gentle shaking in BM2 liquid medium containing 10 mM L-ornithine or 10 mM L-glutamate as sole carbon sources, essentially as described previously (31). The MICs for imipenem of these bacteria were determined by the micro-and macrodilution methods, essentially as described previously (29).…”

Safety Assessment of Transgenic Organisms, Volume 4

“…Carbapenem resistance is generally mediated by class D ß-lactamase such as the OXA-23, -24, -25, -26, -27 and -40 (Van Looveren and Goossens, 2004). Resistance to both imipenem and meropenem in multidrug-resistant clinical strains of A. baumannii can also be associated with changes in the outer membrane composition, such as the loss of a heat-modifiable 29-kDa outer membrane protein designated CarO (Limansky et al, 2002;Mussi et al, 2005), which mediates uptake of carbapenems as well as L-ornithine and other basic amino acids (Mussi et al, 2007). Carbapenem used to be the antibiotic of choice for the treatment of Acinetobacter infections.…”