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In a cohort of 1,209 intensive care unit (ICU) patients, the prevalence of intestinal colonization with high-level expressed AmpC cephalosporinase-producing Enterobacteriaceae (HLAC-PE) rose steadily from 2% at admission to 30% in patients with lengths of stay (LOS) exceeding 4 weeks. In multivariate analysis, LOS was the main predictor of carriage acquisition after adjustment on antimicrobial exposure. HLAC-PE infection occurred in 15% of carriers. Carriage and infection were associated with a marked increase in carbapenem consumption.T he burden of expanded-spectrum cephalosporin (ESC) resistance in Enterobacteriaceae now represents a daily issue for the management of antimicrobial therapy in intensive care unit (ICU) patients (1, 2). Two distinct enzymatic mechanisms may be involved, namely, plasmid-borne extended-spectrum beta-lactamases (ESBL) and high-level expressed AmpC cephalosporinase (HLAC) (2). The HLAC phenotype results from the mutationinduced derepression of a normally low-level expressed chromosomal bla ampC gene or, more rarely, from the horizontal transfer of a plasmid-borne AmpC variant (3). HLAC-producing Enterobacteriaceae (HLAC-PE) currently account for up to 50% of the ESCresistant Enterobacteriaceae responsible for ICU-acquired infections in settings with a high prevalence of ESBL-producing Enterobacteriaceae (ESBL-PE) (4).The intestinal microbiota forms the main reservoir of ESCresistant Enterobacteriaceae in ICU patients (5-7); however, the features of HLAC-PE carriage remain poorly described in this population. Our objectives were to identify the risk factors for HLAC-PE carriage and to appraise its clinical significance in terms of subsequent infections and carbapenem consumption in a large single-center cohort of critically ill patients.This retrospective study was conducted in the 18-bed medicalsurgical ICU of an 1,100-bed teaching hospital in France. During the 3-year study period (2008 to 2010), intestinal carriage of ESCresistant Enterobacteriaceae was routinely screened by rectal swabbing at admission and at weekly intervals afterwards as part of the institutional infection control policy, with implementation of isolation measures in identified carriers. Swabs were discharged in 1 ml of 0.9% saline, and 50 l of the suspension was subsequently plated on a selective medium for ESC-resistant Gram-negative bacilli (chromID ESBL; bioMérieux, Marcy-l'Étoile, France). After overnight incubation at 35°C, colonies were subcultured for identification (API 20E; bioMérieux) and susceptibility testing using the disk diffusion method on Mueller-Hinton agar plates (Bio-Rad, Marnes-la-Coquette, France), in accordance with the French Society of Microbiology guidelines (www.sfm-microbiologie.org). Third-generation cephalosporin -resistant Enterobacteriaceae isolates showing a synergy zone between ESC and clavulanate were categorized as ESBL-PE, while those without synergy and a Ն5-mm increase in the ESC inhibition diameter on cloxacillin-supplemented Mueller-Hinton agar (250 mg · ml Ϫ1 ) were cat...

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