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Antimicrobial Agents and Chemotherapy, February 2005, p. 862-863, Vol. 49, No. 2
0066-4804/05/$08.00+0 doi:10.1128/AAC.49.2.862-863.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
High-Level Resistance to Fluoroquinolones Linked to Mutations in gyrA, parC, and parE in Salmonella enterica Serovar Schwarzengrund Isolates from Humans in Taiwan

LETTER
Recent reports suggest high-level fluoroquinolone (FQ) resistance
is emerging in
Salmonella enterica serovar Typhimurium,
S. enterica serovar Choleraesuis, and
S. enterica serovar Schwarzengrund
in different parts of the world (
1-
9).
In this study we analyzed high-level FQ resistance mechanisms in four S. enterica serovar Schwarzengrund strains which showed resistance levels to ciprofloxacin (Cip) MICs of 16 or 64 µg/ml and were isolated from stools or blood from patients in Taiwan (Table 1). Three of them were also multidrug resistant (Table 1).
Strains CGST2, CGST3, CGST4, and CGST5 carried up to five mutations
in the quinolone target genes relative to those from
S. enterica serovar Typhimurium, i.e., all carried a double mutation in
the quinolone resistance-determining region (QRDR) of
gyrA,
leading to amino acid changes Ser83Phe and Asp87Asn or Asp87Gly,
and a double mutation in the QRDR of
parC, leading to amino
acid changes Thr57Ser and Ser80Arg or Glu84Lys. Two strains
displaying the highest levels of resistance to Cip carried an
additional single mutation in the QRDR of
parE, leading to amino
acid change Ser458Pro. The ParC Thr57Ser amino acid change is
likely not involved in quinolone resistance, because it was
also identified in quinolone-susceptible
S. enterica serovar
Schwarzengrund control strain 383SA99 (Table
1). This amino
acid change was, however, recently reported to be involved in
decreased FQ susceptibility of
S. enterica strains isolated
in Hong Kong (
7). Because we also found this amino acid change
in a quinolone-susceptible
S. enterica serovar Hadar strain
(Table
1), it is probably the result of genetic divergence between
the
parC genes of
S. enterica serovar Typhimurium, serovar Schwarzengrund,
and serovar Hadar rather than being related to quinolone resistance.
The ParC Ser80Arg and Glu84Lys amino acid changes found in the
FQ-resistant
S. enterica serovar Schwarzengrund strains have
also been recently reported in FQ-resistant serovar Typhimurium
isolates from patients in France, Hong Kong, Japan, and Taiwan
(
3,
6,
7,
8). The ParE Ser458Pro amino acid change found in
strains CGST2 and CGST4 was also recently reported for FQ-resistant
S. enterica serovar Typhimurium isolates from patients in Hong
Kong (
7). According to our data, this amino acid change, which
is located at a same position as that found in the homologous
GyrB protein (amino acid change Ser464Phe in FQ-resistant
S. enterica serovar Typhimurium DT204 [
2]), could account for a
two- to fourfold increase in resistance levels to FQs (Table
1). The use of the efflux pump inhibitor Phe-Arg-ß-naphthylamide
(PAßN) decreased the FQ resistance levels 2- to 64-fold
depending on FQ and the strain, suggesting participation of
efflux in high-level FQ resistance (Table
1). The combination
PAßN-enrofloxacin was the most effective in decreasing
the resistance levels, as previously demonstrated (
2).
In conclusion, high-level FQ resistance in S. enterica serovar Schwarzengrund strains appears to be linked to multiple target gene mutations at codon positions 83 and 87 for gyrA, codon positions 80 and 84 for parC, and codon position 458 for parE, as well as being linked to active efflux.

ACKNOWLEDGMENTS
We thank C. Mouline and V. Verbeeren for expert technical assistance.
This study was funded by INRA, projet Transversalité.

REFERENCES
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2 - Baucheron, S., H. Imberechts, E. Chaslus-Dancla, and A. Cloeckaert. 2002. The AcrB multidrug transporter plays a major role in high-level fluoroquinolone resistance in Salmonella enterica serovar Typhimurium phage type DT204. Microb. Drug Resist. 8:281-289.[CrossRef][Medline]
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Sylvie Baucheron
Elisabeth Chaslus-Dancla
Axel Cloeckaert*
Unité BioAgresseurs Santé et Environnement Institut National de la Recherche Agronomique, 37380 Nouzilly France
Cheng-Hsun Chiu
Department of Pediatrics Chang Gung Children's Hospital Kweishan, Taoyuan Taiwan
Patrick Butaye
Centre d'Etude et de Recherches Vétérinaires et Agrochimiques Brussels Belgium
|
| | | | | |
* Phone: 33 2 47 42 77 50 Fax: 33 2 47 42 77 74 E-mail: cloeckae{at}tours.inra.fr |
Antimicrobial Agents and Chemotherapy, February 2005, p. 862-863, Vol. 49, No. 2
0066-4804/05/$08.00+0 doi:10.1128/AAC.49.2.862-863.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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