National epidemiologic surveys of Enterobacter aerogenes in Belgian hospitals from 1996 to 1998

Abstract

Two national surveys were conducted to describe the incidence and prevalence of Enterobacter aerogenes in 21 Belgian hospitals in 1996 and 1997 and to characterize the genotypic diversity and the antimicrobial resistance profiles of clinical strains of E. aerogenes isolated from hospitalized patients in Belgium in 1997 and 1998. Twenty-nine hospitals collected 10 isolates of E. aerogenes, which were typed by arbitrarily primed PCR (AP-PCR) using two primers and pulsed-field gel electrophoresis. MICs of 10 antimicrobial agents were determined by the agar dilution method. Beta-lactamases were detected by the double-disk diffusion test and characterized by isoelectric point. The median incidence of E. aerogenes colonization or infection increased from 3.3 per 1,000 admissions in 1996 to 4.2 per 1000 admissions in the first half of 1997 (P < 0.01). E. aerogenes strains (n = 260) clustered in 25 AP-PCR types. Two major types, BE1 and BE2, included 36 and 38% of strains and were found in 21 and 25 hospitals, respectively. The BE1 type was indistinguishable from a previously described epidemic strain in France. Half of the strains produced an extended-spectrum beta-lactamase, either TEM-24 (in 86% of the strains) or TEM-3 (in 14% of the strains). Over 75% of the isolates were resistant to ceftazidime, piperacillin-tazobactam, and ciprofloxacin. Over 90% of the strains were susceptible to cefepime, carbapenems, and aminoglycosides. In conclusion, these data suggest a nationwide dissemination of two epidemic multiresistant E. aerogenes strains in Belgian hospitals. TEM-24 beta-lactamase was frequently harbored by one of these epidemic strains, which appeared to be genotypically related to a TEM-24-producing epidemic strain from France, suggesting international dissemination.

FIG. 1

Distribution of MICs of ceftazidime (top) and cefepime (bottom) for E. aerogenes isolates (n = 236) according to the presence of plasmid ESBL. Black bars, ESBL-producing strains; white bars, non-ESBL-producing strains.

FIG. 2

Dendrogram of similarity of AP-PCR types of E. aerogenes Belgian isolates (n = 260). a, epidemic types; b, locally epidemic types; c, sporadic types.

FIG. 3

Geographic distribution of E. aerogenes isolates belonging to the 2 major epidemic types. Flanders (upper part of Belgium) is separated from Wallonia (lower part) and Brussels (central position). Diagrams indicate the proportions of AP-PCR type BE 1 (black portions) and BE 2 (white portions) strains by hospitals.

FIG. 4

PFGE profiles of epidemic E. aerogenes isolates grouped by AP-PCR types 1 and 2 and dendrogram of pattern similarity based on the Pearson similarity coefficient.