Carbapenem use is driving the evolution of IMiPenemase (IMP)-1 variants

Metallo-β-lactamases (MBLs) are a growing clinical threat because they inactivate nearly all β-lactam-containing antibiotics, and there are no clinically-available inhibitors. A significant number of variants have already emerged for each MBL subfamily. To understand the evolution of IMiPenemase (IMP) genes (blaIMP) and their clinical impact, twenty clinically-derived IMP-1 like variants were obtained using site-directed mutagenesis and expressed in a uniform genetic background in Escherichia coli DH10B. Strains of IMP-1-like variants harboring S262G or V67F substitutions exhibited increased resistance towards carbapenems and decreased resistance towards ampicillin. Strains expressing IMP-78 (S262G/V67F) exhibited the largest changes in MIC values as compared to IMP-1. In order to understand the molecular mechanisms of increased resistance, biochemical, biophysical, and molecular modeling studies were conducted to compare IMP-1, IMP-6 (S262G), IMP-10 (V67F), and IMP-78 (S262G/V67F). Finally, unlike most NDM and VIM variants, the IMP-1 like variants do not confer any additional survival advantage if zinc availability is limited. Therefore, the evolution of MBL subfamilies (i.e. IMP-6, -10, and -78) appears to be driven by different selective pressures.