Characterization of the AmpC {beta}-lactamase from Burkholderia multivorans [PublishAheadOfPrint]

Burkholderia multivorans is a member of the Burkholderia cepacia complex, a group of >20 related species of nosocomial pathogens that commonly infect individuals suffering from Cystic Fibrosis. β-Lactam antibiotics are recommended as therapy for infections due to B. multivorans, which possesses two β-lactamase genes, bla_penA and bla_AmpC. PenA is a carbapenemase with a substrate profile similar to the Klebsiella pneumoniae carbapenemase (KPC); in addition, expression of PenA is inducible by β-lactams in B. multivorans. Herein, we characterize AmpC from B. multivorans ATCC 17616. AmpC possesses only 38-46% protein identity to non-Burkholderial AmpCs (e.g., PDC-1, CMY-2). Within 49 clinical isolates of B. multivorans, we identified 27 different AmpC variants. Some variants possessed single amino acid substitutions within critical active site motifs (-loop and R2 loop). Purified AmpC1 demonstrated minimal measurable catalytic activity towards β-lactams (i.e., nitrocefin and cephalothin). Moreover, avibactam was a poor inhibitor of AmpC1 (K_{i app} >600 μM) and the acyl-enzyme complex formation with AmpC1 was slow, likely due to lack of productive interactions with active site residues. Interestingly, immunoblotting using a polyclonal anti-AmpC antibody revealed that protein expression of AmpC1 was inducible in B. multivorans ATCC 17616 after growth in sub-inhibitory concentrations of imipenem (1 μg/ml). The AmpC is a unique inducible class C cephalosporinase that may play an ancillary role in B. multivorans compared to PenA, which is the dominant β-lactamase in B. multivorans ATCC 17616.

https://ift.tt/2mm8Ppu