Carbapenem-resistant Serratia marcescens isolates producing Bush group 2f β-lactamase (SME-1) in the United States:: Results from the MYSTIC Programme

Two carbapanem (imipenem, meropenem)-resistant Serratia marcescens strains were isolated in the United States (Chicago, IL) through the 1999 MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) Programme. The S. marcescens antimicrobial susceptible patterns were: susceptible to ceftriaxone, ceftazidime, and cefepime (MICs, less than or equal to0.25 mug/ml), and resistance to the carbapenems (imipenem and meropenem; MIC, > 32 mug/ml) and aztreonam (MIC, greater than or equal to 16 mug/ml). Each S. marcescens isolate shared an identical epidemiologic type (ribotype and PFGE) and the outer membrane protein profile was also identical to those of the wild type susceptible strains from the same medical center. The PCR utilizing bla(sme-1) primers amplified a gene product that was identified as consistent with SME-1 after DNA sequencing. Imipenem and meropenem resistance due to production of carbapenem-hydrolyzing enzymes among clinical isolates is still very rare, but microbiology laboratories should be aware of these chromosomally encoded enzymes among class C p-lactamases producing enteric bacilli such as S. marcescens and Enterobacter cloacae. (C) 2001 Elsevier Science Inc. All rights reserved.