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Letter
Community Transmission of
Extended-Spectrum ß-Lactamase
Beatriz Mirelis,*† Ferran Navarro,*† Elisenda Miró,* Raul Jesús Mesa,*
Pere Coll,*† and Guillem Prats*†
*Hospital de la Santa Creu i Sant Pau, Barcelona, Spain; and †Universitat
Autònoma de Barcelona, Barcelona, Spain
Suggested citation for this article: Mirelis
B, Navarro F, Miró E, Mesa RJ, Coll P, Prats G. Community transmission
of extended-spectrum ß-lactamase. Emerg Infect Dis [serial online]
2003 Aug [date cited]. Available from: URL: http://www.cdc.gov/ncidod/EID/vol9no8/03-0094.htm
To the Editor: The spread of multiresistant gram-negative bacteria
in the general population is a problem of paramount importance, but the
responsible mechanisms are poorly understood. Several studies have focused
on ß-lactam resistance in Enterobacteriaceae isolated from
stools in healthy people, but they did not specifically investigate the
extended-spectrum ß-lactamases (ESBL). Furthermore, none of these
studies detected ESBL in the evaluated population (1,2).
We performed three survey studies to determine the incidence of Enterobacteriaceae
strains producing ESBLs in the stools of outpatients attending our hospital.
The first study was performed during a 4-month period (February–May 2001),
the second during a 3 month-period (April–June 2002), and the third during
1 month (October 2002).
Stool samples were spread onto plates of MacConkey agar containing 2
mg/L of cefotaxime. A colony of each distinct morphotype was analyzed
further. Species were identified according to conventional methods (3).
The susceptibility to ß-lactam antibiotics was determined by the
disk-diffusion test, following recommendations of the National Committee
for Clinical Laboratory Standards (4,5). The interpretative
reading of the antibiogram was performed according to standard guidelines
(4–6). The MICs of cefotaxime and ceftazidime, with and
without clavulanic acid, were later determined by E test (AB Biodisk,
Solna, Sweden). Strains producing ESBL were defined as strains showing
synergism between amoxicillin-clavulanic acid and cefotaxime, ceftazidime,
cefepime, or aztreonam (4,5).
All strains suspected of carrying a resistance pattern compatible with
hyperproduction of the chromosomal enzymes, as well as resistant strains
without synergy, were disregarded. During the first period, 15 (2.1%)
of 707 outpatients were carriers of Escherichia coli (14 patients)
or Proteus mirabilis (1 patient) with ESBL. This percentage increased
during the second period, when 17 (3.8%) of 454 outpatients were carriers
of E. coli with ESBL, and again in the third period, when 12 (7.5%)
of 160 were carriers of E. coli (11 patients) or Enterobacter
cloacae (1 patient) with ESBL. Characterization of the different ESBL
isolated during the three study periods is in process. Although Klebsiella
pneumoniae carrying ESBL has been detected in our hospital (7),
as well as in other hospitals in Barcelona (8), no ESBL-producing
K. pneumoniae strains were identified in this survey.
Although we did not disregard either the patients’ previous treatment
with antibiotics or previous hospitalization, these patients came to the
hospital from the community carrying strains that express ESBL. Moreover,
during these three periods we observed a significant increase in the frequency
of ESBL carriers (from 2.1% to 7.5%; p<0.005). These data suggest that
the community could be a reservoir for these enzymes, as occurs with other
microorganisms (9–11). Many questions remain unanswered
regarding the diffusion mechanisms of this resistance in the community.
Confirmation of community-based transmission of ESBL would indicate a
need for heightened vigilance and further studies to determine the reservoirs
and vehicles for dissemination of ESBL within the community.
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