Carbapenem-induced β-lactamase-isoform expression trends in Acinetobacter baumannii.

Carbapenem-resistant Acinetobacter baumannii (CRAb) is an urgent bacterial threat to public health, with only a few treatment options and a > 50% fatality rate. Although several resistance mechanisms are understood, it is still impossible to predict which mutations are most likely to occur. Here, we demonstrate that independent samples of Ab, exposed to different carbapenems with escalating concentrations, show concentration- and carbapenem-dependent trends in β-lactamase-isoform expression. This result, based on the isoforms identified through label-free-quantification LC-MS/MS measurements of cell-free, gel-separated β-lactamases, suggests that the appearance of antibiotic resistance may be have some predictability based on structural factors. Additionally, the identified minor isoforms also have high sequence similarity to major expressed isoforms, indicating a potential path over which resistance occurred in independent samples. Antibiotic resistance maybe therefore somewhat predictable based on specific structural properties and further investigation may lead to new strategies for mitigating antibiotic resistance.