Increase isolation of Gram-negative bacilli resistant to broad-spectrum cephalosporin has been observed during the last few years, thus determining the use of more potent beta-lactams, such as carbapenems. The use of these antimicrobial agents may lead to the emergence of carbapenem resistant Gram-negative bacilli in the nosocomial environment. Carbapenem resistance may be due to the production of Ambler class D beta-lactamase or Ambler class B beta-lactamase, also called metallo-beta-lactamase (MbetaL). Apart from the monobactam aztreonam, this class of enzyme virtually hydrolyze all the commercially available beta-lactams. Since 90s, several clinical important nosocomial microorganisms, including members of Enterobacteriaceae family, Pseudomonas spp. and Acinetobacter spp., have been found to produce MbetaLs enzymes. When these carbapenem non-susceptible strains are found, they may be submitted to phenotypic MbetaL detection test in the microbiology laboratory in order to help infection control practioners and prevent the MbetaL gene dissemination, once these genes are embedded in mobile genetic elements, which can spread rapidly to other Gram-negative species.

Gram-negative bacilli; Carbapenem resistance; Metallo-beta-lactamase; Integron; Gene cassette

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