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Antimicrobial Agents and Chemotherapy, December 2003, p. 3942-3944, Vol. 47, No. 12
0066-4804/03/$08.00+0 DOI: 10.1128/AAC.47.12.3942-3944.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Single and Double Mutations in gyrA but Not in gyrB Are Associated with Low- and High-Level Fluoroquinolone Resistance in Helicobacter pylori
Jacques Tankovic,1* Christine Lascols,2 Quentin Sculo,2 Jean-Claude Petit,1 and Claude-James Soussy2
Laboratoire
de Bactériologie, Centre Hospitalo-Universitaire Saint-Antoine,
Assistance Publique-Hôpitaux de Paris, Université
Paris VI, Paris,1
Laboratoire de
Bactériologie, Centre Hospitalo-Universitaire
Henri-Mondor, Assistance Publique-Hôpitaux de Paris,
Université Paris XII, Créteil,France2
Received 5 August 2003/
Returned for modification 3 September 2003/
Accepted 9 September 2003

ABSTRACT
In
one French hospital the rate of resistance to ciprofloxacin
in
Helicobacter pylori was 3.3% (2 of 60 strains) in 1999.
The
six resistant clinical strains (four from 1996 and two from
1999)
and three ciprofloxacin-selected single-step mutants studied
carried
one
gyrA mutation but none in
gyrB. Clinafloxacin and
garenoxacin
were the most active fluoroquinolones against these
mutants.
Occurrence of a second
gyrA mutation was associated
with high
MICs of all fluoroquinolones
tested.

TEXT
Failures of proton pump inhibitor-based triple therapies for
eradication
of
Helicobacter pylori are frequently due to resistance
to
either clarithromycin or metronidazole. Furthermore, coresistance
to
both drugs is not exceptional, particularly after failure
of first-line
therapy (
9). Alternative
regimens in case of coresistance
have thus to be developed. Among
fluoroquinolones, ciprofloxacin
and levofloxacin demonstrate good in
vitro activity against
H. pylori
(
12). In one study,
levofloxacin was shown to be an
effective alternative to clarithromycin
in triple therapies
(
5).
Several other fluoroquinolones, such as clinafloxacin or
gemifloxacin,
appear to be even more active in vitro than ciprofloxacin
against
wild-type
H. pylori
(
10,
12).
Acquired
ciprofloxacin resistance already exists in H. pylori, but the
prevalence of this phenomenon is poorly documented, and no data for
France exist. The mechanisms implicated have been examined in only two
studies, one concerning clinical strains
(11) and the other
concerning laboratory mutants
(15), linking resistance
to the occurrence of a gyrA mutation. It is not known how
gyrA mutations affect the activities of the newer
fluoroquinolones. The eventual role of gyrB mutations has not
yet been examined.
In this work, our goals were to determine the
rate of primary resistance to ciprofloxacin in one French hospital, to
appreciate the respective roles of gyrA and gyrB
mutations in resistance, and to compare the in vitro activity of
ciprofloxacin to those of seven newer fluoroquinolones against
ciprofloxacin-susceptible strains as well as genetically characterized
mutants.
Sixty clinical strains of H. pylori isolated in
Henri Mondor hospital in 1999 were screened for resistance to
ciprofloxacin (defined by an MIC higher than 1 µg/ml
[6]) by plating
10 µl of a suspension calibrated at 3 McFarland units on horse
blood-supplemented (10%) Mueller-Hinton agar containing 1
µg of ciprofloxacin per ml. Two strains grew after 72
h of incubation, growth involved the totality of the inoculum for both
strains, and the rate of resistance was thus 3.3% (2
of 60 strains). Rates of resistance lower than 10% were also
reported from northern, eastern, and southern European countries: The
Netherlands (7), Germany
(9), Bulgaria
(3), Spain
(14), and Portugal
(4).
We then
determined, by the agar dilution method as described previously
(8), the MICs of
ciprofloxacin and of seven newer fluoroquinolones for nine
ciprofloxacin-susceptible clinical strains from 1999 chosen at random,
for the two ciprofloxacin-resistant isolates from 1999 (328R and 361R),
and for four other resistant strains isolated in 1996 (H14R, H23R,
H67R, and HboR). Against susceptible strains, compared to
ciprofloxacin, moxifloxacin was 2- to 4-fold less active, levofloxacin
was as active, trovafloxacin, gatifloxacin, and garenoxacin were 1- to
4-fold more active, gemifloxacin was 2- to 4-fold more active, and
clinafloxacin was 4- to 16-fold more active (Table
1). The resistant strains could be separated in two groups. The first group
included four strains (H14R, H23R, H67R, and HboR) for which the MICs
of garenoxacin, gemifloxacin, and clinafloxacin remained relatively
low: 1 to 2, 1 to 4, and 0.5 to 1 µg/ml, respectively. The
relative potency of garenoxacin against these resistant strains was
higher than those of other fluoroquinolones (Table
1). The two strains of the
second group (328R and 361R) presented a higher level of resistance to
all the fluoroquinolones tested except ciprofloxacin (Table
1). Thus, the levels of
resistance of these two strains to ciprofloxacin, garenoxacin,
gemifloxacin, and clinafloxacin were similar.
View this table:
[in this window]
[in a new window]
|
TABLE 1. Phenotypic
and genotypic characteristics of fluoroquinolone-susceptible and
-resistant strains of H. pylori
|
We amplified by PCR
and sequenced the quinolone resistance-determining
regions (QRDRs) of
the
gyrA (from codon 38 to 154) and
gyrB (from codon
392 to 500) genes from the six resistant strains.
The
gyrA
primers used were 5'-TTTRGCTTATTCMATGAGCGT
and 5'-GCAGACGGCTTGGTARAATA,
and
the
gyrB primers were
5'-YGCAAAAGCCAGAGAAGCCA and
5'-ACATGCCCTTGTTCAATCAGC.
The
sizes of the amplified fragments of
gyrA and
gyrB
were 428
and 444 bp, respectively. One
gyrA mutation was found
in all
resistant strains, but no
gyrB mutation was found
(Table
1).
The
gyrA mutations detected had already been reported by Moore
et
al. (
11). In agreement
with their results, we found that
the most common mutation in
H.
pylori was at Asp91, and we were
able to confirm the role of these
mutations in resistance by
transformation of susceptible isolate 325S
with the PCR-amplified
gyrA fragments of resistant strains
(data not presented). Only
one
gyrA mutation was detected in
strains 328R and 361R, which
presented a higher level of resistance to
newer fluoroquinolones
than the other resistant clinical
strains, thus suggesting that
an additional resistance
mechanism could exist in these strains.
They could carry a second
mutation in the DNA topoisomerase
IV
parC or
parE
gene. However, this enzyme may not exist in
H. pylori because
the two genome sequences of
H. pylori available
(
1,
13)
do not contain the
parC or
parE gene. Active efflux also appears
unlikely
because in one study it was found that efflux did not play any
role
in resistance to antibiotics in
H. pylori
(
2). These strains
could
perhaps carry a
gyrA or
gyrB mutation in a region
distinct
from the QRDRs.
By sequencing the QRDRs of the
ciprofloxacin-susceptible strains, we observed that amino acid
variations not implicated in resistance could exist in the QRDRs of
both GyrA and GyrB. This was not reported before, but it is important
to differentiate these variations from resistance-related alterations.
Three were observed in GyrA: the most important is the variation
Asn
Thr at resistance hot spot position 87, and the two others
are Ala97
Val and Arg140
Lys. Three were also observed
in GyrB: Ser479
Gly, Asp481
Glu, and
Arg484
Lys.
Single-step mutants were obtained from
ciprofloxacin-susceptible isolate 325S by plating 200 µl of a
suspension calibrated at 5 McFarland units on horse blood-supplemented
B2 agar (Oxoid, Dardilly, France) containing 1 µg of
ciprofloxacin per ml, and three were chosen at random for study. We
observed that resistant mutants with phenotypes and genotypes similar
to those observed in clinical strains could be obtained in vitro in one
selection step (Table 1).
Furthermore, high-level-fluoroquinolone-resistant mutants were obtained
by plating resistant strains H23R and H328R onto
clinafloxacin-containing agar. Two of the mutants obtained, H23RM1 and
328RM1, deriving from H23R and 328R, respectively, were selected for
further study. MICs of all fluoroquinolones for both mutants were high,
and this was associated with the occurrence of a second gyrA
mutation (Table 1). To our
knowledge, the existence of highly fluoroquinolone-resistant H.
pylori gyrA double mutants has never yet been
reported.
In conclusion, our work shows that fluoroquinolone
resistance of H. pylori already exists in France but remains
rare and that gyrA single or double mutations have a critical
role in this resistance. It also shows that among newer
fluoroquinolones clinafloxacin, gemifloxacin, and garenoxacin are
markedly more active than ciprofloxacin against susceptible strains and
some but not all gyrA mutants.

FOOTNOTES
* Corresponding
author. Mailing address: Laboratoire de Bactériologie,
Hôpital Saint-Antoine, 184 rue du Faubourg Saint-Antoine, 75571
Paris Cedex 12, France. Phone: 33 1 49 28 29 10. Fax: 33 1 49 28 24 72.
E-mail:
jacques.tankovic{at}sat.ap-hop-paris.fr.


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Antimicrobial Agents and Chemotherapy, December 2003, p. 3942-3944, Vol. 47, No. 12
0066-4804/03/$08.00+0 DOI: 10.1128/AAC.47.12.3942-3944.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
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