Carbapenem-resistant Serratia marcescens isolates producing Bush Group 2f -lactamase (SME-1) in the United States: Results from the MYSTIC Programme Ana C. Gales a , Douglas J. Biedenbach a,c , Patricia Winokur b , Donna M. Hacek d , Michael A. Pfaller a,c , Ronald N. Jones a,c, * a Department of Pathology, University of Iowa College of Medicine, Iowa City, Iowa b Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa c CAST Laboratories, Iowa City, Iowa d Departments of Medicine and Pathology, Northwestern University, Chicago, Illinois Received 30 October 2000; accepted 15 November 2000 Abstract Two carbapenem (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 suscep- tible patterns were: susceptible to ceftriaxone, ceftazidime, and cefepime (MICs, 0.25 g/ml), and resistance to the carbapenems (imipenem and meropenem; MIC,  32 g/ml) and aztreonam (MIC, 16 g/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 -lactamases producing enteric bacilli such as S. marcescens and Enterobacter cloacae. © 2001 Elsevier Science Inc. All rights reserved. 1. Introduction Serratia marcescens has become an important nosoco- mial organism acting as an opportunistic pathogen to cause diverse types of serious infections (Hejazi & Falkiner, 1997). The therapeutic use of -lactams for infections caused by S. marcescens can be limited due to production of chromosomal class C -lactamases that are generally induc- ible, but may become stably derepressed thus producing additional resistance to some broad-spectrum cephalospo- rins (Jones, 1998). Resistance to newer cephalosporins among S. marcescens isolates has also been reported sec- ondary to the production of class A extended-spectrum -lactamases (ESBL) (Kunugita et al., 1995), and when resistance to these cephalosporins emerges (either due to an ESBL or elevated class C -lactamase production), the carbapenems have been treatment options (Jones, 1998). Among the Enterobacteriaceae, the rare occurrences of carbapenem resistances arise via two mechanisms: 1) high level production of class C chromosomal cephalosporinase combined with altered outer membrane permeability de- scribed in S. marcescens, Enterobacter cloacae, Enter- obacter aerogenes, and Providencia rettgeri isolates (Jones, 1998; Weindorf et al., 1998); and 2) resistance resulting from the synthesis of -lactamases capable of hydrolyzing carbapenems (Ito et al., 1995; Rasmussen & Bush, 1997; Yang et al., 1990). Resistance to carbapenems due to car- bapenem-hydrolyzing enzymes has been described in S. marcescens isolates in the United States (US) and Europe (Queenan et al., 2000; Yang et al., 1990). In contrast, emergence of carbapenem resistance in Japan among S. marcescens has reached a prevalence of 3.8% in certain areas, where dissemination of a plasmid mediated bla imp metallo--lactamase has occurred (Ito et al., 1995). In this report, we describe the mechanism of resistance to * Corresponding author. The Jones Group, 345 Beaver Kreek Center, Suite A, North Liberty, IA 52317 Tel.: +1-319-665-3370; fax: +1-319- 665-3371. E-mail address: ronald-jones@jonesgr.com. (R.N. Jones). www.elsevier.com/locate/diagmicrobio Diagnostic Microbiology and Infectious Disease 39 (2001) 125–127 0732-8893/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0732-8893(00)00222-4