Ciprofloxacin-resistant Salmonella enterica Serotype Typhi, United States, 1999-2008.
ABSTRACT We report 9 ciprofloxacin-resistant Salmonella enterica serotype Typhi isolates submitted to the US National Antimicrobial Resistance Monitoring System during 1999-2008. The first 2 had indistinguishable pulsed-field gel electrophoresis patterns and identical gyrA and parC mutations. Eight of the 9 patients had traveled to India within 30 days before illness onset.
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ABSTRACT: We characterized Salmonella enterica serovar Typhi isolates from Bangladesh, Indonesia, Taiwan and Vietnam to investigate their genetic relatedness and antimicrobial resistance. The isolates from Bangladesh and Vietnam were genetically closely related but distant from those from Indonesia and Taiwan. All but a few isolates from Indonesia and Taiwan were susceptible to all antimicrobials tested. The majority of isolates from Bangladesh and Vietnam were multidrug resistant (MDR) and belonged to the widespread haplotype H58 clone. IncHI1 plasmids were detected in all MDR S. Typhi from Vietnam but in only 15% of MDR isolates from Bangladesh. Resistance genes in the majority of MDR S. Typhi from Bangladesh should reside in the chromosome. Of the isolates from Bangladesh, 82% and 40% isolates were resistant to varying concentrations of nalidixic acid and ciprofloxacin, respectively. Several resistance mechanisms including alterations in gyrase A, the presence of QnrS and enhanced efflux pumps were involved in the reduced susceptibility and resistance to fluoroquinolone. Intensive surveillance is necessary to monitor the spread of the chromosome-mediated MDR and fluoroquinolone-resistant S. Typhi emerging in Bangladesh.Antimicrobial Agents and Chemotherapy 08/2014; · 4.57 Impact Factor
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ABSTRACT: Introduction: Enteric fever is endemic in Nepal and poses a significant public health burden. The first-line drugs ampicillin, chloramphenicol, and cotrimoxazole have not been part of empirical therapy for two decades due to the development of multidrug-resistant Salmonella strains. The objective of this study was to determine the antibiogram pattern of Salmonella serovars isolated from the blood of clinically suspected enteric fever patients. Methodology: A cross sectional study was carried out in a tertiary care hospital in Lalitpur, Nepal, between July 2011 and February 2012. Standard microbiological procedures were followed during collection and processing of blood samples, isolation and identification of Salmonella serotypes. The antimicrobial sensitivity of ampicillin, chloramphenicol, cotrimoxazole, nalidixic acid, and ciprofloxacin was determined using a modified Kirby-Bauer disk diffusion method as per the guidelines of the Clinical and Laboratory Standards Institute. Results: Out of 86 Salmonella isolates, 56 (65.1%) were Salmonella Typhi and 30 (34.9%) were Salmonella Paratyphi A. Salmonella Typhi were 100% sensitive to chloramphenicol, cotrimoxazole, and ciprofloxacin and 98.2% sensitive to ampicillin. Similarly, Salmonella Paratyphi A isolates were 100% sensitive to ampicillin and cotrimoxazole and 96.7% sensitive to chloramphenicol and ciprofloxacin. More than 90.0% of isolates were nalidixic acid resistant and none of the Salmonella isolates were multi-drug resistant. Conclusions: This study revealed the increasing frequency of nalidixic acid-resistant Salmonella isolates, indicating the possibility of fluoroquinolone resistance in near future. Furthermore, re-emergence of susceptibility to conventional first-line drugs ampicillin, chloramphenicol, and cotrimoxazole supports the possibility of using these drugs in empirical therapy.The Journal of Infection in Developing Countries 11/2014; 2014(8(11)):1483-1487. · 1.00 Impact Factor
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ABSTRACT: Salmonella enterica serotype Typhi (S. Typhi) is an enteric pathogen that causes typhoid fever. The infection can be severe, with significant morbidity and mortality, requiring antimicrobial therapy. Cases of S. Typhi infection in the United States and other developed countries are often associated with travel to endemic regions. The empirical use of first-line drugs for therapy, including ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole, has resulted in transmissible multidrug resistance. With the global increase in multidrug-resistant S. Typhi, use of ciprofloxacin, with excellent oral absorption, few side effects, and cost-effectiveness, has become popular for treatment. However, decreased ciprofloxacin susceptibility due to point mutations in the S. Typhi genes gyrA and/or parC has caused treatment failures, necessitating alternative therapeutic options. S. Typhi is typically genetically homogenous, with phylogenetic and epidemiological studies showing that identical clones and diverse S. Typhi types often coexist in the same geographic region. Studies investigating point mutations have demonstrated that selective pressure from empirical use of first-line drugs and fluoroquinolones has led to the global emergence of haplotype H-58. Antibiotic resistance is subject to high selective pressure in S. Typhi and thus demands careful use of antimicrobials.Annals of the New York Academy of Sciences 07/2014; · 4.38 Impact Factor
Ciprofl oxac in-
S erotype Typhi,
United S tates,
Felicita Medalla, Maria Sjölund-Karlsson,
Sanghyuk Shin, Emily Harvey, Kevin Joyce,
Lisa Theobald, Benjamin L. Nygren,
Gary Pecic, Kathryn Gay, Jana Austin,
Andrew Stuart, Elizabeth Blanton, Eric D. Mintz,
Jean M. Whichard, and Ezra J. Barzilay
We report 9 ciprofl oxacin-resistant Salmonella enterica
serotype Typhi isolates submitted to the US National
Antimicrobial Resistance Monitoring System during
1999–2008. The fi rst 2 had indistinguishable pulsed-fi eld
gel electrophoresis patterns and identical gyrA and parC
mutations. Eight of the 9 patients had traveled to India
within 30 days before illness onset.
rare in the United States in the era of modern sanitation
(1,2). However, typhoid fever remains common in many
developing countries. In the United States, 72%–81% of
patients with typhoid fever report international travel in the
month before illness onset (1,3–5). Highest risk has been
associated with travel to southern Asia (1–5).
Fluoroquinolones (e.g., ciprofl oxacin) are frequently
used to treat typhoid fever in adults (4,6). Ciprofl oxacin
resistance is rare; however, resistance to the quinolone
nalidixic acid in the US National Antimicrobial Resistance
Monitoring System (NARMS) increased from 19% of
isolates tested in 1999 to 59% in 2008 (7). Nalidixic
acid resistance in S. enterica serotype Typhi, which
has been associated with overseas travel, particularly to
southern Asia, correlates with decreased susceptibility to
yphoid fever, caused by Salmonella enterica serotype
Typhi, is a systemic bacterial illness that has been
ciprofl oxacin (MIC >0.12 μg/mL) (4–6,8). Increased risk
for fl uoroquinolone treatment failure has been demonstrated
in Salmonella infections from strains with decreased
susceptibility to ciprofl oxacin (6,8,9). Chromosomal point
mutations in the gyrA and parC topoisomerase genes
are mechanisms of quinolone resistance in Salmonella
spp. Other resistance mechanisms include effl ux pumps,
reduced outer membrane permeability, and plasmid-borne
genes (e.g., qnr, aac-6′-Ib-cr genes) (6,8,10–12). We report
9 ciprofl oxacin-resistant (MIC >4 μg/mL) S. enterica
serotype Typhi isolates detected in the United States during
State public health laboratories receive Salmonella
isolates from clinical diagnostic laboratories as part of routine
surveillance. State and local health department offi cials
report demographic, clinical, and travel information about
laboratory-confi rmed typhoid fever on a standard form
to the Centers for Disease Control and Prevention (CDC,
Atlanta, GA, USA). Participating states began submitting
all S. enterica serotype Typhi isolates to NARMS in
1999; since 2003, all state public health laboratories have
participated. Isolates were tested for susceptibility by using
broth microdilution (Sensititre: Trek Diagnostics, Westlake,
OH, USA). MICs were determined for 15 antimicrobial
agents and interpreted by using Clinical and Laboratory
Standards Institute (CLSI) criteria when available (Table
1) (7,13). For ciprofl oxacin-resistant isolates, subtyping by
pulsed-fi eld gel electrophoresis (PFGE) was performed by
using the protocol established by the National Molecular
Subtyping Network for Foodborne Disease Surveillance
(PulseNet) (14). PFGE pattern similarity was assessed by
cluster analysis (Dice, UPGMA [unweighted pair group
method using arithmetic averages]) and band-matching
applications of BioNumerics software (Applied Maths,
Sint-Martens-Latem, Belgium) and confi rmed by visual
comparison (Figure). For ciprofl oxacin-resistant isolates
detected for 1999–2005, sequencing of the quinolone
resistance–determining region (QRDR; defi ned as amino
acids 67–106 for gyrA) was performed according to the
methods described by Crump et al. (6), and additional
patient information (e.g., antimicrobial drug treatment) was
requested by using a questionnaire with institutional review
During 1999–2005, we detected 2 (0.1%) cases of
ciprofl oxacin resistance among 1,690 S. enterica serotype
Typhi isolates. Case reports follow.
In 2003, a 1-year-old girl had onset of fever 1 day
before arriving in the United States from India. A blood
specimen collected 3 days after fever onset yielded S.
enterica serotype Typhi. Diarrhea or vomiting at time of
specimen collection was not reported. Information about
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 6, June 2011 1095
Author affi liations: Centers for Disease Control and Prevention,
Atlanta, Georgia, USA (F. Medalla, M. Sjölund-Karlsson, K. Joyce,
L. Theobald, B.L. Nygren, G. Pecic, K. Gay, J. Austin, A. Stuart,
E. Blanton, E.D. Mintz, J.M. Whichard, E.J. Barzilay); California
Emerging Infections Program, Oakland, California, USA (S. Shin);
and Massachusetts Department of Public Health, Jamaica Plain,
Massachusetts, USA (E. Harvey)
antimicrobial drug treatment was not available. The child
was hospitalized for 14 days.
In 2005, a 2-year-old girl had onset of diarrhea,
which was treated with ofl oxacin, 2 days before she
arrived in the United States from India. Seven days later,
she continued to have diarrhea, and fever, vomiting, and
abdominal cramps developed. She was hospitalized and
treated with antimicrobial agents, including ciprofl oxacin.
Blood and fecal specimens collected 3 weeks after illness
onset yielded S. enterica serotype Typhi. The patient was
discharged after 14 days of hospitalization. She had lived
in India for 6 months before traveling to the United States.
The S. enterica serotype Typhi isolates were resistant
to ciprofl oxacin (Tables 1, 2) and had indistinguishable
PFGE patterns when restriction enzymes XbaI and
BlnI were used: PulseNet-designated XbaI pattern
JPPX01.0026 and BlnI pattern JPPA26.0110 (Table
2; Figure). QRDR sequencing showed gyrA mutations
resulting in a serine to tyrosine substitution at codon 83
and an aspartic acid to asparagine substitution at codon
87, and a parC mutation conferring a serine to isoleucine
substitution at codon 80.
Seven (0.6%) ciprofl oxacin-resistant infections were
detected among patients from whom 1,131 S. enterica
serotype Typhi isolates were submitted during 2006–2008
(Table 2). The 7 cases occurred in 2006 and 2007. Patients
were a median of 22 years of age (range 5–48 years); 5
(71%) were male. All 6 patients with known travel histories
reported travel to India in the 30 days before illness onset.
In addition to XbaI JPPX01.0026 and BlnI JPPA26.0110, 3
different XbaI and BlnI pattern combinations were detected
in the 7 isolates (Table 2; Figure).
We describe ciprofl oxacin-resistant S. enterica
serotype Typhi isolates from 9 patients in the United
States. The fi rst 5 cases were reported previously in
aggregated form, without molecular characterization
of the isolates (5). The fi rst 2 patients were young
children apparently infected in India in 2003 and 2005.
1096 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 6, June 2011
Table 1. MICs of antimicrobial agents tested for 9 ciprofloxacin-resistant Salmonella enterica serotype Typhi isolates detected in the
National Antimicrobial Resistance Monitoring System, United States, 1999–2008
MIC, μg/mL,* by patient no. (isolate)
(MA-03) (CA-05) (CA-06)
Ciprofloxacin >4 >4>4
Nalidixic acid >32>32>32
Amoxicillin-clavulanic acid <1/0.5 <1/0.5<1/0.5
Ceftiofur 0.5 0.5 0.5
Folate pathway inhibitors
Tetracycline >32>32 <4
*Classes of antimicrobial agents defined by the Clinical and Laboratory Standards Institute (CLSI) were used to categorize agents (7,13). MICs were
interpreted by using CLSI criteria when available (7,13): ciprofloxacin (resistance breakpoint, >4 μg/mL); nalidixic acid (>32); amikacin (>64); gentamicin
(>16); kanamycin (>64); amoxicillin-clavulanic acid (>32/16); cefoxitin (>32); ceftiofur (>8); ceftriaxone (>4); sulfamethoxazole/sulfisoxazole (>512);
trimethoprim-sulfamethoxazole (>4/76); ampicillin (>32); chloramphenicol (>32); and tetracycline (>16). For streptomycin, resistance was defined as MIC
>64 μg/mL (7). If growth was not inhibited by the highest concentration of the agent in the panel, the MIC was reported as above the highest
†Isolate was cultured from a blood specimen. Another isolate was cultured from fecal samples, which had MIC <0.5 μg/mL for amikacin and same MICs
for other agents tested.
‡Sulfamethoxazole was used during 1999–2003 and sulfisoxazole since 2004 to represent sulfonamides.
Antimicrobial class and agent*
Patient 2† Patient 3 Patient 4
8/4<1/0.5 <1/0.5 <1/0.5 <1/0.5<1/0.5
Ciprofl oxacin-Resistant S. enterica ser. Typhi
Six additional patients, who were detected in 2006 and
2007, also reported travel to India. Travel to the Indian
subcontinent has been associated with nalidixic acid–
resistant S. enterica serotype Typhi infection; however,
ciprofl oxacin-resistant infections are rarely reported by
using current CLSI criteria (4,5,11). Other resistance
patterns were fi rst described in southern Asia, where the
incidence of typhoid fever is high and antimicrobial agents
are widely available without prescription, providing the
opportunity for the development and selection of resistant
Other than reports by 8 patients of travel to India,
we have no information about possible shared exposures,
such as specifi c locations visited, sources of food or water,
or contact with carriers of S. enterica serotype Typhi.
However, the indistinguishable PFGE XbaI and BlnI
patterns and identical gyrA and parC mutations of isolates
from the fi rst 2 patients suggest that, although typhoid
fever occurred nearly 2 years apart, the same ciprofl oxacin-
resistant strain is likely to have been involved. After 2005,
different XbaI and BlnI patterns have been identifi ed in
ciprofl oxacin-resistant isolates, indicating independent
selection of ciprofl oxacin resistance in different strains.
The gyrA and parC mutations of isolates from the fi rst 2
patients were reported in ciprofl oxacin-resistant S. enterica
serotype Typhi in India (11). The 2 gyrA mutations are well
characterized and known to be associated with quinolone
resistance; 2 point mutations in gyrA and 1 in parC confer
fl uoroquinolone resistance (8,10–12). Further studies,
including characterization of other resistance mechanisms,
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 6, June 2011 1097
Figure. Pulsed-fi eld gel electrophoresis (PFGE) XbaI (A) and BlnI (B) patterns of 9 ciprofl oxacin-resistant Salmonella enterica serotype
Typhi isolates detected in the National Antimicrobial Resistance Monitoring System, 1999–2008. PFGE pattern similarity was assessed by
cluster analysis (Dice, UPGMA [unweighted pair group method using arithmetic average]) and band-matching applications of BioNumerics
software (Applied Maths, Sint-Martens-Latem, Belgium) and confi rmed by visual comparison. PulseNet only considers band markings
found within the scale of the global standard, which are all bands between 20.5 kb and 1,135 kb. The cluster parameters are Dice
coeffi cient and UPGMA with the tolerance of band position of 1.5% and optimization of 1.5%.
Table 2. Patient and isolate description, resistance to other antimicrobial agents, PFGE pattern, and travel reported for 9 ciprofloxacin-
resistant Salmonella enterica serotype Typhi infections detected in the National Antimicrobial Resistance Monitoring System, United
(isolate) sex Site collection year source
1 (MA-03) 1/F MA2003 BloodCot, Fis, Nal, Tet
2 (CA-05) 2/F CA 2005 BloodCot, Fis, Nal, Tet
3 (CA-06) 26/FCA2006 Blood
4 (TX-06) 8/MTX2006 Blood Amp, Chl, Cot,
Age, y/ SpecimenSpecimen Resistance to
Fis, Nal, Str
Cot, Fis, Nal, Tet
Cot, Fis, Nal, Tet
*PFGE, pulsed-field gel electrophoresis. State/local public health laboratories that submitted isolates: MA, Massachusetts; CA, California; TX, Texas; AZ,
Arizona; NYC, New York City; NJ, New Jersey; LAC, Los Angeles County, California. Resistance to antimicrobial agents other than ciprofloxacin: Cot,
trimethoprim–sulfamethoxazole; Fis, sulfamethoxazole or sulfisoxazole; Nal, nalidixic acid; Tet, tetracycline; Amp, ampicillin; Chl, chloramphenicol; Str,
†National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet)–designated PFGE patterns using restriction enzyme XbaI (data
as of 2009 Oct 21): JPPX01.0026, the most common XbaI pattern among 3,233 isolates with reported XbaI pattern in PulseNet, was detected in 486
(15.0%); JPPX01.0465 and JPPX01.0506 each were detected in 12 (0.4%) isolates.
‡PulseNet-designated PFGE patterns using restriction enzyme BlnI (data as of 2009 Oct 21): JPPA26.0002, the most common BlnI pattern among 409
isolates with reported BlnI pattern in PulseNet, was detected in 61 (14.9%) isolates; JPPA26.0110 was detected in 5 (1.2%), JPPA26.0187 was detected
in 3 (0.7%), and JPPA26.0170 was detected in 1 (0.2%).
§Travel outside the United States reported in the 30 d before illness onset; patient 4 also traveled to Bangladesh and the United Arab Emirates.
are needed to track the evolution of fl uoroquinolone-
resistant S. enterica serotype Typhi.
Although the ciprofl oxacin resistance we detected
using current CLSI criteria is rare in S. enterica serotype
Typhi, nalidixic acid resistance, which correlates with
decreased susceptibility to ciprofl oxacin, has increased (7).
Clinicians should be aware that infection with Salmonella
spp. with decreased susceptibility to ciprofl oxacin may
not respond satisfactorily to this agent (6,8,9,13,15). In
addition, identifi cation of ciprofl oxacin-resistant cases has
been increasing. In the presence of quinolone resistance,
third-generation cephalosporins, such as ceftriaxone,
can be used (2,6,8,15). Recent clinical trials suggest that
azithromycin might be useful for treating uncomplicated
typhoid fever (2,8,9,15). Recommendations for empiric
treatment of typhoid fever in the United States are best
developed by using information about antimicrobial drug
resistance trends in isolates from countries where the
infection was acquired.
We thank the health departments and public health
laboratories in the 50 states; Los Angeles County, California; New
York City, New York; and Houston, Texas, for their participation
in NARMS, the National Typhoid Fever Surveillance System,
and PulseNet. We are grateful to Matthew Mikoleit, Susan Van
Duyne, Nancy Garrett, and Efrain Ribot for their assistance.
The US Food and Drug Administration provides funding
support for NARMS.
Dr Medalla is an epidemiologist with the Division of
Foodborne, Waterborne, and Environmental Diseases, National
Center for Emerging and Zoonotic Infectious Diseases, Centers
for Disease Control and Prevention. Her main research interests
include antimicrobial resistance in foodborne pathogens.
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Address for correspondence: Felicita Medalla, Centers for Disease
Control and Prevention, 1600 Clifton Rd NE, Mailstop D63, Atlanta, GA
30333, USA; email: email@example.com
1098 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 6, June 2011