Molecular epidemiological study of nosocomial Enterobacter aerogenes isolates in a Belgian hospital

Abstract

In 1995, the rate of isolation of Enterobacter aerogenes in the Saint-Pierre University Hospital in Brussels, Belgium, was higher than that in the preceding years. A total of 45 nosocomial E. aerogenes strains were collected from 33 patients of different units during that year, and they were isolated from 19 respiratory specimens, 13 pus specimens, 7 blood specimens, 4 urinary specimens, 1 catheter specimen, and 1 heparin vial. The strains were analyzed to determine their epidemiological relatedness and were characterized by their antibiotic resistance pattern determination, plasmid profiling, and genomic fingerprinting by macrorestriction analysis with pulsed-field gel electrophoresis (PFGE). The majority of the strains (82%) were multiply resistant to different commonly used antibiotics. Two major plasmid profiles were found: most strains (64%) harbored two plasmids of different sizes, whereas the others (20%) contained a single plasmid. PFGE with SpeI and/or XbaI restriction enzymes revealed that a single clone (80%) was responsible for causing infections or colonizations throughout the year, and this result was concordant with those obtained by plasmid profiling, with slight variations. By comparing the results of these three methods, PFGE and plasmid profiling were found to be the techniques best suited for investigating the epidemiological relatedness of E. aerogenes strains, and they are therefore proposed as useful tools for the investigation of nosocomial outbreaks caused by this organism.

FIG. 1

PFGE fingerprints of 45 E. aerogenes isolates (1995) after digestion with the XbaI restriction enzyme (A) and the SpeI restriction enzyme (B). Lane FH54 to lane BG64, profile IA and profile IB (broadly clone I); lane FH51 to lane FH90, profiles IIA, IIB, and IIC (broadly, clone II); lane FH49 to lane FH77, unrelated strains (nonclonal); lanes M, molecular size markers (PFGE marker I, λ ladder).

FIG. 2

Dendrogram generated from PFGE patterns of nosocomial E. aerogenes strains (n = 45) by Molecular Analyst Software Fingerprinting, version 1.0. Major clones are designated with arabic numerals, and subtypes are indicated by letter suffixes. Clustering was done with the unweighted pair group method with arithmatic averages algorithm by using fine correlation on gel tracks.

FIG. 3

Incidence of E. aerogenes at Saint-Pierre University Hospital from January 1994 to December 1996.