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Journal of Clinical Microbiology, 01 1997, 152-160, Vol 35, No. 1
Y De Gheldre, N Maes, F Rost, R De Ryck, P Clevenbergh, JL Vincent and MJ Struelens
Molecular typing was used to investigate an outbreak of infection caused by
multidrug-resistant Enterobacter aerogenes (MREA) susceptible only to
gentamicin and imipenem in an intensive care unit (ICU). Over a 9-month
period, ciprofloxacin-resistant E. aerogenes isolates were isolated from 34
patients, or 4.1% of ICU admissions, compared with a baseline rate of 0.1%
in the previous period (P < 0.001). Infection developed in 15 (44%)
patients. In vivo emergence of imipenem resistance (MIC, 32 micrograms/ml)
of organisms causing deep-seated infection was observed in two (13%) of
these patients following prolonged therapy with imipenem and gentamicin.
Arbitrarily primed PCR (AP-PCR) analysis with ERIC1R and ERIC2 primers and
pulsed-field gel electrophoresis (PFGE) analysis of XbaI macrorestriction
patterns concordantly showed that outbreak-associated MREA isolates were
clonally related and distinct from epidemiologically unrelated strains.
AP-PCR and PFGE showed discrimination indices of 0.88 and 0.98,
respectively. Space-time clustering of cases within units suggests that the
epidemic-related MREA isolates were transmitted on the hands of the health
care personnel. A case-control study and repeated environmental culture
surveys failed to identify a common source or procedure associated with
transmission. In spite of the early implementation of isolation measures,
the incidence of MREA colonization remained stable until all colonized
patients were discharged. This study confirms the usefulness of AP-PCR and
PFGE analyses for the epidemiological study of E. aerogenes and underscores
the difficulty of controlling the spread of multiresistant clones of this
organism in the ICU setting. The emergence of imipenem resistance
represents a threat because virtually no therapeutic option is available
for such strains.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Molecular epidemiology of an outbreak of multidrug-resistant Enterobacter aerogenes infections and in vivo emergence of imipenem resistance
Department of Microbiology, Erasme Hospital, Brussels, Belgium.
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