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Journal of Clinical Microbiology, August 2008, p. 2794-2795, Vol. 46, No. 8
0095-1137/08/$08.00+0 doi:10.1128/JCM.00676-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Extended-Spectrum-Beta-Lactamase Production in a Salmonella enterica Serotype Typhi Strain from the Philippines
Nashwan Al Naiemi,1*
Bastiaan Zwart,2
Martine C. Rijnsburger,1
Robert Roosendaal,1
Yvette J. Debets-Ossenkopp,1
Janet A. Mulder,1
Cees A. Fijen,2
Willemina Maten,2
Christina M. Vandenbroucke-Grauls,1 and
Paul H. Savelkoul1
Department of Medical Microbiology and Infection Control, VU University Medical Center, Amsterdam,1
Regional Microbiological Laboratory, Zaandam, The Netherlands2
Received 9 April 2008/
Returned for modification 23 May 2008/
Accepted 30 May 2008

ABSTRACT
A
Salmonella enterica serotype Typhi strain was cultured from
blood and fecal samples from a 54-year-old man with fever and
diarrhea. He had returned from travel to the Philippines a few
days earlier. Phenotypic and genotypic analysis confirmed the
production of the SHV-12 extended-spectrum beta-lactamase.

TEXT
Resistance to cephalosporins, due to the production of extended-spectrum
β-lactamases (ESBLs), is an ever increasing problem and
is a cause of serious concern worldwide. So far, these enzymes
have been detected in many species of the family
Enterobacteriaceae,
including different serovars of
Salmonella enterica (
11). To
the best of our knowledge, however, ESBL production in
Salmonella enterica serovar Typhi is as yet unknown.
Salmonella serovar
Typhi is the causative agent of typhoid fever, a severe systemic
Salmonella infection with high rates of morbidity and mortality,
especially in tropical and subtropical countries. Infection
occurs by the ingestion of contaminated water or food. Through
the use of proper sanitation and hygiene measures and effective
antimicrobial chemotherapy, the rates of morbidity and mortality
from typhoid fever have been greatly reduced in developed countries,
while large outbreaks still occur in developing countries (
6).
Salmonella spp. are usually susceptible to many antimicrobial
agents, but a recent increase in the rates of resistance raises
are of concern (
14). The prevalence of multidrug-resistant
Salmonella serovar Typhi is also increasing among travelers who have returned
from areas where
Salmonella serovar Typhi is endemic (
4). We
isolated a strain of
S. enterica serotype Typhi from blood and
fecal samples from a 54-year-old Dutch man who was admitted
to the Waterland Hospital in Purmerend, The Netherlands, at
the end of November 2007, with signs and symptoms of typhoid
fever. These symptoms started 2 weeks after he had returned
from a 2-month visit to the Philippines. The patient was successfully
treated with ciprofloxacin at 500 mg orally twice daily for
3 weeks. The
Salmonella serovar Typhi strain was resistant to
extended-spectrum cephalosporins but was sensitive to amoxicillin-clavulanate.
We investigated whether the resistance to the extended-spectrum
cephalosporins was due to the production of an ESBL.
The strain was identified as S. enterica serotype Typhi with the Vitek-2 system (BioMerieux, Boxtel, The Netherlands) and by agglutination with Salmonella antisera (Remel, United Kingdom). Genomic species determination was confirmed by partial 500-bp sequence analysis of the 16S rRNA gene and by DNA fingerprinting by amplified fragment length polymorphism analysis (12). Antibiotic susceptibilities were determined according to the guidelines of the Clinical Laboratory Standards Institute with the Vitek-2 system (BioMerieux) and Etest (AB Biodisk, Solna, Sweden). ESBL production was detected by a combined disk test (10) and ESBL Etest (AB Biodisk). The ESBL genes were identified by PCR; and subsequent sequence analysis was performed with SHV-, TEM-, and CTX-M-specific primers, which detect the blaSHV, blaTEM, and blaCTX-M genes, respectively, as described previously (1, 2).
Phenotypically, the strain was resistant to gentamicin, tobramycin, piperacillin, and trimethoprim-sulfamethoxazole and was sensitive to amoxicillin-clavulanate, ciprofloxacin, meropenem, and piperacillin-tazobactam (Table 1). This strain was also sensitive to chloramphenicol, which is remarkable, as Salmonella species are frequently resistant to this antibiotic. PCR and sequence analysis revealed the presence of the genes for SHV-12 and TEM-1. The SHV-12 ESBL enzyme differs from the SHV-1 enzyme by three amino acids substitutions, and it was first described in a Klebsiella pneumoniae strain isolated in Switzerland (8). The SHV-12 ESBL is one of the most common non-CTX-M ESBLs and is identified in many gram-negative species, including Salmonella species (2, 15). TEM-1 is the most commonly encountered beta-lactamase in the Enterobacteriaceae, and it is able to hydrolyze narrow-spectrum penicillins and cephalosporins, such as cephalothin and cephaloridine (10). ESBL production was detected in Salmonella enterica strains of different serovars in several countries, like Italy, France, and Nepal; however, to the best of our knowledge, this is the first report to describe an infection caused by an ESBL-producing S. enterica serotype Typhi strain.
Typhoid fever is a serious systemic infectious disease with
high rates of morbidity and mortality and requires optimal antimicrobial
therapy. Multidrug resistance among
S. enterica serotype Typhi
strains is increasing, especially in Southeast Asia (
5) and
in the Middle East and northeastern Africa (
3,
7,
9). Extended-spectrum
cephalosporins, in particular, ceftriaxone, are the drugs of
choice for the treatment of infections due to ampicillin- and
fluoroquinolone-resistant
Salmonella serovar Typhi (
13). The
emergence of an ESBL in
S. enterica serotype Typhi constitutes
a new challenge. This emergence may be explained by the exchange
of mobile genetic elements, such as plasmids and transposons,
between enteric bacteria and is selected for by the antimicrobial
agents used for humans, especially extended-spectrum cephalosporins.
Since ESBL genes are nearly always located on mobile genetic
elements, further rapid spread among
Salmonella strains is to
be expected.
We provide evidence of the production of an ESBL, SHV-12, in Salmonella enterica serotype Typhi due to the presence of a blaSHV gene. This is a worrisome finding with potential serious clinical implications, since the dissemination of this resistance trait will further hamper the therapeutic possibilities for the treatment of typhoid fever.

FOOTNOTES
* Corresponding author. Mailing address: Department of Medical Microbiology and Infection Control, VU University Medical Center, De Boelelaan 1117, Amsterdam 1081 HV, The Netherlands. Phone: 31-20-4440488. Fax: 31-20-4440473. E-mail:
n.alnaiemi{at}vumc.nl 
Published ahead of print on 11 June 2008. 

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Journal of Clinical Microbiology, August 2008, p. 2794-2795, Vol. 46, No. 8
0095-1137/08/$08.00+0 doi:10.1128/JCM.00676-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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