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Antimicrobial Agents and Chemotherapy, June 2006, p. 2251-2254, Vol. 50, No. 6
0066-4804/06/$08.00+0 doi:10.1128/AAC.00123-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Fluoroquinolone-Resistant Urinary Isolates of Escherichia coli from Outpatients Are Frequently Multidrug Resistant: Results from the North American Urinary Tract Infection Collaborative Alliance-Quinolone Resistance Study
James A. Karlowsky,1,2*
Daryl J. Hoban,1,2
Melanie R. DeCorby,2
Nancy M. Laing,2 and
George G. Zhanel2
Department
of Clinical Microbiology, Health Sciences Centre/Diagnostic Services of
Manitoba,1
Department of
Medical Microbiology and Infectious Diseases, Faculty of Medicine,
University of Manitoba, Winnipeg, Manitoba,
Canada2
Received 31 January 2006/
Returned for modification 6 March 2006/
Accepted 21 March 2006

ABSTRACT
Ciprofloxacin-resistant
Escherichia coli isolates (
n = 1,858)
from outpatient midstream urine specimens at 40 North American
clinical
laboratories in 2004 to 2005 were frequently resistant
to ampicillin
(79.8% of isolates) and trimethoprim-sulfamethoxazole
(66.5%);
concurrent resistance to cefdinir (9.0%) or nitrofurantoin
(4.0%) was
less common. Only 10.8% of isolates were resistant
to ciprofloxacin
alone. Fluoroquinolone-resistant isolates of
E. coli from
urine were frequently multidrug
resistant.

TEXT
The most recently published in vitro surveillance data from
centers
across the United States and Canada indicate that approximately
10 to
25% of urinary tract isolates of
Escherichia coli from
female
outpatients are resistant to trimethoprim-sulfamethoxazole
(SXT)
(
3,
7,
10,
11,
12,
21,
22,
25,
26). Culture selection
and
sample selection biases inherent in published urinary isolate
surveillance
studies and hospital antibiograms have been summarized
previously
(
8). Resistance
to SXT may complicate the management of urinary
tract infections
(
20), and physician
concern regarding resistance
to SXT
(
24) has resulted in
fluoroquinolones and nitrofurantoin
being more frequently prescribed as
empirical therapy for cystitis
(
7,
9,
15).
Currently, the
majority of urinary isolates of E. coli and most other
uropathogens causing uncomplicated cystitis and pyelonephritis in the
United States and Canada remain susceptible to fluoroquinolones
(5,
10,
11,
12,
21,
22,
25,
26); however, the
prevalence of fluoroquinolone-resistant isolates of E. coli
has been reported to be increasing over time in some centers in the
United States and Canada
(3,
7,
11,
12,
13,
18,
23,
25), and resistance rates
have been shown to vary markedly by center, with some hospital
laboratories reporting >25% of their E. coli isolates
as fluoroquinolone resistant
(3,
23). Given that a
transition in the therapy for outpatient urinary tract infections may
be occurring, or appears imminent
(7,
8,
9,
15), and that
fluoroquinolone-resistant isolates of E. coli are not uncommon
in some centers, we determined the in vitro susceptibilities of
prospectively collected fluoroquinolone-resistant midstream urine
isolates of E. coli from outpatients to other agents used for
the treatment of acute cystitis because these isolates may be
encountered by clinicians and no prospective study specifically
studying fluoroquinolone-resistant isolates has been
published.
From January 2004 to June 2005,
fluoroquinolone-resistant E. coli isolates from midstream
urine specimens from outpatients were collected from 30 medical centers
in the United States (n = 1,483) and from 10 Canadian
medical centers (n = 375)
(25). Each isolate was
deemed to be a significant urinary tract isolate by each participating
laboratory's urine culture algorithm. Isolates and limited demographic
information (patient gender and age) were submitted to the Health
Sciences Centre in Winnipeg, Canada, where the isolates were confirmed
to be E. coli by conventional methodology
(17) and where Clinical
and Laboratory Standards Institute-specified broth microdilution
testing was performed with ampicillin, cefdinir, ciprofloxacin,
ertapenem, nitrofurantoin, and SXT
(2,
16). Of the 1,858
isolates tested, 1,440 (77.5%) were from females, 30 (1.6%) were from
patients <15 years of age, 470 (25.3%) were from patients 15 to
50 years of age, and 1,358 (73.1%) were from patients >50 years
of age. Statistical analyses were performed by
2
testing with Epi Info Statcalc, version 6.0 (Centers for Disease
Control and Prevention); P values of <0.05 were
reported as statistically significant.
The MICs at which 50% of
isolates were inhibited (MIC50s),
MIC90s, MIC ranges, and overall rates of
resistance for the 1,858 ciprofloxacin-resistant E. coli
isolates are provided in Table
1. Of the orally available
agents tested, ampicillin (79.8%) and SXT (66.5%) demonstrated the
highest rates of resistance; resistance to nitrofurantoin (4.0%) and
cefdinir (9.0%) was less frequent. All isolates were susceptible to
ertapenem, a parenteral carbapenem.
View this table:
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TABLE 1. Rates
of resistance to ampicillin, cefdinir, ertapenem, nitrofurantoin, and
SXT in a 2004 to 2005 collection of 1,858 outpatient midstream urine
isolates of E. coli resistant to ciprofloxacin
|
Approximately 78% of isolates
(
n = 1,447) had ciprofloxacin
MICs of

32
µg/ml, with 17% of isolates (
n = 321) having
ciprofloxacin
MICs of

128 µg/ml. When isolates were
placed into three
groups based upon ciprofloxacin MICs (4 to 16, 32 to
64, and

128 µg/ml), increasing rates of resistance to
ampicillin
(from 73.0 to 80.2 to 87.5%) (
P < 0.01),
cefdinir (from 3.2
to 2.0 to 23.1%) (
P < 0.01), and
nitrofurantoin (from 4.4
to 2.7 to 8.1%) (
P < 0.01)
were observed; the rates of resistance
to SXT were similar (68.4, 66.6,
and 65.4%, respectively) (
P > 0.05) regardless of
ciprofloxacin MIC (Table
1). Although
no isolates
resistant to ertapenem were identified, the ertapenem
MIC
90
increased from

0.015 µg/ml to 0.12 µg/ml for
isolates
with ciprofloxacin MICs of 4 to 16 and 32 to 64 µg/ml
compared
to isolates with ciprofloxacin MICs of

128
µg/ml.
When isolates were grouped by patient age into
three groups (<15, 15 to 50, and >50 years), the
percentages of isolates with ciprofloxacin MICs of 4 to 16, 32 to 64,
and
128 µg/ml were similar (P > 0.05)
for each age group (<15 years, 2.2, 1.7, and 0.6%; 15 to 50
years, 25.1, 25.8, and 24.0%; >50 years, 72.7, 72.6, and 75.4%)
(data not shown). When isolates were grouped by patient gender, the
ratios of males to females were similar (P > 0.05) for
those isolates with ciprofloxacin MICs of 4 to 16 µg/ml (males,
19.8%; females, 80.2%) and 32 to 64 µg/ml (males, 21.8%;
females, 78.2%), but in comparison with those ratios ciprofloxacin MICs
of
128 µg/ml were more commonly associatedwith males and less commonly with females (males, 29.8%; females,
70.2%) (P < 0.01) (data not shown).
Table
2 depicts the numbers of
ciprofloxacin-resistant isolates that were susceptible to all other
agents tested (10.8% of isolates) or concurrently resistant to one
(27.3%), two (54.1%), three (7.4%), or four (0.4%) other oral
antimicrobial agents and the relative contributions of each agent to
multidrug-resistant phenotypes. Approximately 90% of isolates resistant
to ciprofloxacin were also resistant to at least one or two additional
agents, most commonly ampicillin and SXT. Resistance to cefdinir and
nitrofurantoin was most common in ciprofloxacin-resistant isolates
already resistant to ampicillin and SXT. The ciprofloxacin
MIC50s, MIC90s, and MIC ranges for each of the
five groups in Table 2
(resistance to ciprofloxacin and zero, one, two, three, and four
additional agents) were 32, 64, and 4 to
128 µg/ml;
32, 128, and 4 to
128 µg/ml; 32, 128, and 4 to
128 µg/ml; 64,
128, and 4 to
128
µg/ml; and 128, 128, and 16 to 128 µg/ml, respectively
(data not shown).
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TABLE 2. Resistance
to one or more additional oral antimicrobial agents in a 2004 to 2005
collection of 1,858 outpatient midstream urine isolates of E.
coli resistant to ciprofloxacin
|
Previously published retrospective studies have
demonstrated
that a ciprofloxacin-resistant phenotype without
concurrent
resistance to other classes of antimicrobials, including
ampicillin,
SXT, and nitrofurantoin, was uncommon among outpatient
isolates
of
E. coli
(
4,
10,
11,
12,
21,
22,
26), that by pulsed-field
gel
electrophoresis analysis fluoroquinolone-resistant
E. coli
isolates
were genomically diverse
(
4), and that associations
between
fluoroquinolone resistance and other resistance determinants
such
as extended-spectrum ß-lactamases
(
14,
19) may be
emerging. The
majority of ciprofloxacin-resistant isolates in
the present study
(73.1%) were isolated from patients aged >50
years. This
observation was not unexpected given that fluoroquinolones
are more
commonly prescribed to older patients (>50 years
of age) than
younger patients (
15,
21). The present study
and
previously published reports both suggest that fluoroquinolone
resistance
typically arises in isolates of
E. coli already
harboring ampicillin
and/or SXT resistance determinants. The clonal
expansion of
multidrug-resistant isolates may be furthered by exposure
to
any single agent for which resistance exists. Currently, it
is
unknown if the selection of fluoroquinolone-resistant mutants
of
E.
coli is more frequent for multidrug-resistant isolates
than for
pansusceptible isolates.
In conclusion, in vitro resistance to
fluoroquinolones appears to be increasing in some hospitals and regions
and is associated with multidrug-resistant phenotypes. Close attention
is required to monitor fluoroquinolone susceptibility patterns and the
association of multidrug resistance with fluoroquinolone resistance in
isolates of E. coli and other bacteria causing urinary tract
infections and other infections. The broad-spectrum activity and
convenience of use of fluoroquinolones are well recognized; however,
increased prescription of fluoroquinolones as first-line therapy for
common infections such as cystitis will facilitate the emergence of
resistance to this class of compounds and promote the emergence of
multidrug-resistant strains and, therefore, should be discouraged as it
will undermine the efficacy of fluoroquinolones to treat
more-serious infections
(1,
6,
7,
8,
15).
Fluoroquinolone-sparing agents should be given higher priority
than fluoroquinolones in the treatment of cystitis
(8). Continued
surveillance of urinary tract isolates of E. coli and other
pathogens is important, and appropriate clinical use of
fluoroquinolones is imperative as they become more widely prescribed
(9). SXT remains
first-line empirical therapy for female outpatients with acute
uncomplicated bacterial cystitis
(8,
24).

ACKNOWLEDGMENTS
We thank the investigators and laboratory site
staff at each
medical center that participated in the North American
Urinary
Tract Infection Collaborative Alliance-Quinolone Resistance
study.
The medical centers (investigators) in the United States were
as
follows: Stanford Hospital and Clinics, Stanford, CA (E.
J.
Baron); Geisinger Medical Center, Danville, PA (P. Bourbeau);
University
of California, San Francisco, CA (G. Brooks); UCLA Medical
Center,
Los Angeles, CA (D. Bruckner and J. Hindler); Johns Hopkins
Hospital,
Baltimore, MD (K. Carroll); Creighton University Medical
Center/St.
Joseph's Hospital, Omaha, NB (S. Cavalieri); University of
Tennessee
Medical Center/Dynacare Tennessee, Knoxville, TN (M. Cole);
ARUP
Laboratories Inc., Salt Lake City, UT (A. Croft); Columbia
Presbyterian
Medical Center, New York, NY (P. Della-Latta); Summa
Health
System, Akron, OH (J. Di Persio); University of Rochester
Medical
Center/Strong Memorial Hospital, Rochester, NY (D. Hardy);
Memorial
Hospital of Rhode Island, Pawtucket, RI (J. Heelan);
Iowa Methodist
Medical Center, Des Moines, IA (A. Herring); Medical
College
of Wisconsin/Froedtert Memorial Lutheran Hospital, Milwaukee,
WI
(S. Kehl); University of North Carolina Hospitals, Chapel Hill,
NC
(M. Miller); University of Kentucky Hospital, Lexington,
KY (S.
Overman); Shands Hospital/University of Florida, Gainesville,
FL (K.
Rand); Mount Sinai Medical Center, New York, NY (I. Rankin);
Audie
Murphy VA Hospital, San Antonio, TX (M. Rinaldi); Laboratory
Sciences
of Arizona, Tempe, AZ (M. Saubolle); University of
Illinois Medical
Center at Chicago, Chicago, IL (P. Schreckenberger);
Dartmouth-Hitchcock
Medical Center, Lebanon, NH (J.
Schwartzman); University of
Texas Medical Branch, Galveston, TX (M.
Smith); New Hanover
Regional Medical Center, Wilmington, NC (G.
Steinkraus); Barnes-Jewish
Hospital, St. Louis, MO (J. Vetter);
University of Alabama at
Birmingham, Birmingham, AL (K. Waites); Emory
University School
of Medicine/Grady Memorial Hospital, Atlanta, GA (Y.
Wang);
Fletcher Allen Health Care, Burlington, VT (W. Washington Jr.);
Denver
Health Medical Center, Denver, CO (M. Wilson); and St. Luke's
Hospital,
Jacksonville, FL (J. Yao). The medical centers
(investigators)
in Canada were as follows: Royal University Hospital,
Saskatoon,
SK (J. Blondeau); Queen Elizabeth II Health Sciences Centre,
Halifax,
NS (R. Davidson); Centre Hospitalier Universitaire de
Sherbrooke,
Sherbrooke, QC (J. Dubois); Health Sciences Centre/St.
Boniface
General Hospital, Winnipeg, MB (D. Hoban); Victoria General
Hospital,
Victoria, BC (P. Kibsey); South East Health Care Corp.,
Moncton,
NB (M. Kuhn); Hôpital Maisonneuve-Rosemont, Montreal,
QC
(M. Laverdière); Mount Sinai Hospital, Toronto, ON
(D. Low);
University of Alberta Hospitals, Edmonton, AB (R.
Rennie); and Ottawa
General Hospital, Ottawa, ON (K. Ramotar).
The study was
financially supported in part by Procter & Gamble (Cincinnati,
OH).

FOOTNOTES
* Corresponding
author. Mailing address: Department of Clinical Microbiology, Health
Sciences Centre, MS673C, 820 Sherbrook Street, Winnipeg, Manitoba R3A
1R9, Canada. Phone: (204) 787-4597. Fax: (204) 787-4699. E-mail:
jkarlowsky{at}hsc.mb.ca.


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Antimicrobial Agents and Chemotherapy, June 2006, p. 2251-2254, Vol. 50, No. 6
0066-4804/06/$08.00+0 doi:10.1128/AAC.00123-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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