Abstract
Twenty-nine IMP-type β-lactamases (IMPs) have been identified in at least 26 species of clinically important Gram-negative bacilli from more than 24 countries/regions. Most of blaIMP genes are harbored by class 1 integrons that are usually embedded in transposons and/or plasmids, footnoting their horizontal transfer and worldwide distribution. blaIMP genes usually co-exist with other resistance genes, such as aacA, catB, and blaOXA, resulting in multi-drug resistance. Compared to other gene cassettes, 76.3% of the blaIMP gene cassettes are located adjacent to Pc promoter of the class 1 integrons, indicating that the blaIMP genes are readily expressed in most of bacterial hosts.