Epidemiology and genetics of VIM-type metallo-β-lactamases in Gram-negative bacilli

Metallo-beta-lactamases (MBLs) are a rapidly evolving group of beta-lactamases, which hydrolyze most beta-lactams including the carbapenems. Of the known MBLs, VIMs are one of the most common families, with 27 variants detected in at least 23 species of Gram-negative bacilli from more than 40 countries/regions. The amino acid similarities of VIM variants range from 72.9 to 99.6% with 1-72 different residues. Most of the bla(VIM)s are harbored by a class 1 integron, a genetic platform able to acquire and express gene cassettes. The integrons are usually embedded in transposons and, in turn, accommodated on plasmids, making them highly mobile. Integrons display considerable diversity, with at least 110 different structures associated with the gain and spread of the bla(VIM)s. In most instances, the bla(VIM)s co-exist with one or more other resistance genes. The processes for the identification of bacteria harboring bla(VIM)s are also discussed in this article.