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Applied and Environmental Microbiology, December 2008, p. 7439-7441, Vol. 74, No. 23
0099-2240/08/$08.00+0 doi:10.1128/AEM.00949-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Seagulls of the Berlengas Natural Reserve of Portugal as Carriers of Fecal Escherichia coli Harboring CTX-M and TEM Extended-Spectrum Beta-Lactamases
Patricia Poeta,1,2,5
Hajer Radhouani,1,5
Gilberto Igrejas,3,4
Alexandre Gonçalves,1
Carlos Carvalho,3,4
Jorge Rodrigues,1,2
Laura Vinué,5
Sergio Somalo,5 and
Carmen Torres5*
University of Trás-os-Montes and Alto Douro, Veterinary Science Department, Vila Real, Portugal,1
Center of Studies of Animal and Veterinary Sciences, Vila Real, Portugal,2
University of Trás-os-Montes and Alto Douro, Department of Genetics and Biotechnology, Vila Real, Portugal,3
Institute for Biotechnology and Bioengineering, Center of Genetics and Biotechnology, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal,4
Biochemistry and Molecular Biology Unit, University of La Rioja, Logroño, Spain5
Received 25 April 2008/
Accepted 28 September 2008

ABSTRACT
Escherichia coli isolates containing the following extended-spectrum
beta-lactamases have been detected in 11 of 57 fecal samples
(19.3%) in Berlengas Island seagulls: TEM-52 (eight isolates),
CTX-M-1 (one isolate), CTX-M-14a (one isolate), and CTX-M-32
(one isolate). Most of the extended-spectrum beta-lactamase-positive
isolates harbored class 1 or class 2 integrons, which included
different antibiotic resistance gene cassettes.

INTRODUCTION
The emergence and wide dissemination of extended-spectrum beta-lactamases
(ESBLs) among clinical
Escherichia coli isolates in hospitals
in recent years are of great concern and represent a problem
for the treatment of infectious diseases (
19). It has also been
reported that
E. coli isolates containing ESBLs, mostly of the
CTX-M class, are frequently detected in community patients (
4)
and have also been found in food-producing animals and household
pets (
2,
3,
5,
8,
11,
14,
17,
24). Moreover, a previous report
identified ESBLs in fecal
E. coli isolates of wild animals (
9),
mainly in birds of prey, but seagulls were not included in that
study. ESBLs seem to be widely distributed in bacteria of different
ecosystems, although more information is needed, especially
for wild ecosystems. The purpose of our study was to analyze
the carriage of ESBL-containing
E. coli isolates in fecal samples
of Berlengas Island seagulls and also to characterize the type
of ESBLs and the phylogenetic groups of isolates. Berlengas
Island is part of the Berlengas Natural Reserve, located 5.7
miles from the Portuguese coast, and it belongs to the National
Network of Protected Areas. Fishermen inhabited the island in
the past, but currently nobody lives there year round, although
some tourists visit the island and a few people stay for vacations.
Diverse species of seagulls make their nests on this island;
in the last few years the population of seagulls has increased
significantly and is considered a true plague (
18).
Fifty-seven fresh seagull fecal droppings were obtained in different areas of the Berlengas Island during September 2007 and were tested for the presence of ESBL-containing E. coli isolates. Fecal samples were seeded in Levine agar plates supplemented with cefotaxime (CTX; 2 µg/ml), and colonies with typical E. coli morphology were selected and identified by classical biochemical methods and by the API 20E system (bioMérieux, La Balme Les Grottes, France). Susceptibility of the recovered E. coli isolates to 16 antibiotics (ampicillin, amoxicillin plus clavulanic acid, cefoxitin, CTX, ceftazidime, aztreonam, imipenem, gentamicin, amikacin, tobramycin, streptomycin, nalidixic acid, ciprofloxacin, sulfamethoxazole-trimethoprim, tetracycline, and chloramphenicol) was tested by the disk diffusion method (7). E. coli ATCC 25922 was used as a quality control strain. Broad-spectrum cephalosporin-resistant isolates were selected for further studies (one isolate per sample), and they were screened for ESBL production according to the CLSI criteria (7).
The presence of genes encoding TEM, SHV, OXA, CTX-M, and CMY type beta-lactamases was studied by specific PCRs (1, 13, 23). All obtained amplicons were sequenced on both strands, and sequences were compared with those included in the GenBank database and in the website http://www.lahey.org/Studies/ to identify the beta-lactamase genes. The genetic environment of blaCTX-M genes was also tested by PCR and by sequencing with previously reported primers (10, 15, 22).
The presence of other antibiotic resistance genes, associated with chloramphenicol (cmlA), tetracycline (tetA and tetB), streptomycin (aadA), and sulfonamide (sul1, sul2, and sul3) resistance, among our isolates was also analyzed by PCR and sequencing (21). The presence of the intI1 and intI2 genes, encoding class 1 and 2 integrases, respectively, and the composition of the variable regions of class 1 and 2 integrons were studied by PCR and sequencing (21). The identification of the major phylogenetic groups among our isolates was determined by PCR (6). Positive and negative controls from the bacterial collection of the University of La Rioja, Logroño, Spain, were used in all assays.
E. coli isolates were detected in Levine CTX plates from 11 of the 57 (19.3%) fecal samples studied. All 11 isolates obtained from these samples were intermediate or resistant to CTX and/or ceftazidime and had a positive screening test for ESBL production. Only 1 of the 11 E. coli isolates (GV-10) showed resistance to amoxicillin plus clavulanic acid. The beta-lactamase genes detected in these isolates were the following (numbers of isolates are in parentheses): blaTEM-52 (8), blaCTX-M-1 plus blaOXA-1 (1), blaCTX-M-14a (1), and blaCTX-M-32 (1) (Table 1). It is interesting that 73% of the ESBL-positive isolates of seagulls harbored the blaTEM-52 gene and that 27% of the isolates harbored the blaCTX-M gene. A high prevalence of TEM-52 has also been recently observed in E. coli isolates from healthy food-producing animals and chicken meat products from Portugal (16).
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TABLE 1. Characteristics of the ESBL-positive fecal E. coli isolates recovered from seagulls of Berlengas Island in Portugal
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Different genetic environments surrounding the
blaCTX-M genes
were detected (Fig.
1). The sequence of the fragment obtained
by PCR upstream of the
blaCTX-M-1 gene in the
E. coli GV-23
strain revealed the presence of a region of the IS
26 transposase
flanking a partially truncated IS
Ecp1 followed by an intergenic
region; this whole structure has been previously found in
E. coli (
13,
22). The presence of IS
Ecp1 and IS
903 surrounding
the
blaCTX-M-14a gene in
E. coli GV-10 was identified, and the
genetic environment of the
blaCTX-M-32 gene detected in
E. coli GV-12 included IS
Ecp1/IS
5 upstream of the
bla gene and
orf477 downstream, as also detected by others (
25).
A variety of resistance genes (
cmlA,
tetA,
tetB,
aadA,
sul1,
sul2, and
sul3) were observed among our ESBL-producing
E. coli isolates (Table
1). Five isolates harbored class 1 integrons
with the following gene cassettes in their variable regions:
dfrA1 plus
aadA1 (two isolates),
sat plus
psp plus
aadA2 (one
isolate),
sat plus
aadA1 (1 isolate), and
blaOXA-1 plus
aadA1 (one isolate). Five isolates harbored class 2 integrons, and
the gene cassette arrangement
dfrA1 plus
sat plus
aadA1 was
identified in all of them.
E. coli GV-8 contained simultaneously
class 1 and 2 integrons. Eight of the ESBL-positive isolates
corresponded to the A and B1 phylogenetic groups, two isolates
corresponded to the D group, and only one
blaTEM-52 isolate
was assigned to the B2 phylogenetic group (Table
1). Previous
studies have reported the association of
E. coli isolates of
the B2 group with extraintestinal infections (
20), and the fecal
origin of our isolates could explain the low prevalence of this
phylogroup.
It is important to note the high prevalence and moderate diversity of ESBLs detected in fecal E. coli from seagulls that inhabit a natural reserve, as is the case for Berlengas Island. As previously indicated, the population of seagulls on an island that is not too far away from the Portuguese coast has significantly increased in recent years. The possibility that these animals eat the remains of human food cannot be excluded. This study gives new evidence for the wide dissemination of ESBLs in E. coli isolates from wild animals, as is the case for seagulls. More studies of this nature should be performed in the future to analyze the prevalence of this type of resistant bacteria in different ecosystems.

ACKNOWLEDGMENTS
This work was partly financed by project SAF2006-14207-C02 of
the Ministry of Science and Education of Spain. We also thank
Pfizer for partial financial support. L. Vinué was supported
by a fellowship from the Spanish Ministry of Education and Science
(SAF2006-14207-C02-01), and S. Somalo was supported by a fellowship
from the Government of La Rioja, Spain (Colabora 2007/15).

FOOTNOTES
* Corresponding author. Mailing address: Área de Bioquímica y Biología Molecular, Universidad de La Rioja, Madre de Dios 51, 26006 Logroño, Spain. Fax: 34-941299721. Phone: 34-941299750. E-mail:
carmen.torres{at}unirioja.es 
Published ahead of print on 3 October 2008. 

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Applied and Environmental Microbiology, December 2008, p. 7439-7441, Vol. 74, No. 23
0099-2240/08/$08.00+0 doi:10.1128/AEM.00949-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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