-
Occurrence of Antibiotic Resistant Uropathogenic Escherichia
coli Clonal Group A 1
in Wastewater Effluents 2
3
Laura A. Boczek1, Eugene W. Rice
1, Brian Johnston
2, and James R. Johnson
2* 4
1U.S. Environmental Protection Agency, Cincinnati OH 5
2*Medical Service, Veterans Affairs Medical Center and
Department of Medicine, 6
University of Minnesota, Minneapolis MN 7
8
9
*Corresponding author address: 10
11
James R. Johnson, M.D. 12
Infectious Diseases (111F) 13
Minneapolis VA Medical Center 14
1 Veterans Drive 15
Minneapolis, MN 55417 (USA) 16
phone: 612-467-4185 17
fax: 612-727-5995 18
email: [email protected] 19
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Copyright © 2007, American Society for Microbiology and/or the
Listed Authors/Institutions. All Rights Reserved.Appl. Environ.
Microbiol. doi:10.1128/AEM.02225-06 AEM Accepts, published online
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Abstract 20
21
Isolates of Escherichia coli belonging to clonal group A (CGA),
a recently 22
described disseminated cause of drug-resistant urinary tract
infections in humans, were 23
present in four of seven sewage effluents collected from
geographically dispersed areas 24
of the United States. All 15 CGA isolates (1% of the 1,484
isolates analyzed) exhibited 25
resistance to trimethoprim-sulfamethoxazole, accounting for 19.5
% of the 77 TMP-26
SMZ-resistant isolates. Antimicrobial resistance patterns,
virulence traits, O:H serotypes, 27
and phylogenetic groupings were compared for CGA and selected
non-CGA isolates. 28
The CGA isolates exhibited a wider diversity of resistance
profiles and somatic antigens 29
than found in most previous characterizations of this clonal
group. This is the first report 30
of recovery from outside a human host of CGA E. coli isolates
with virulence factor and 31
antibiotic resistance profiles typical of human-source CGA
isolates. The occurrence of 32
"human-type" CGA in wastewater effluents demonstrates a
potential mode for the 33
dissemination of this clonal group in the environment, with
possible secondary 34
transmission to new human or animal hosts. 35 ACCE
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Introduction 36
37
Resistance to commonly prescribed antimicrobial agents is a
matter of increasing 38
concern. Along with respiratory infections, urinary tract
infections (UTIs) are the most 39
common bacterial infections in the United States requiring
antimicrobial therapy. 40
Escherichia coli is the most frequently isolated etiological
agent of UTIs and 41
trimethoprim-sulfamethoxazole (TMP-SMZ) is one of the primary
antibiotics which is 42
empirically prescribed for the treatment of community-acquired
UTIs (6). In the United 43
States there has been a notable increase in the isolation of
uropathogenic E. coli resistant 44
to TMP-SMZ (6). This finding is of particular interest since
resistance to this drug is 45
generally associated with resistance to additional antibiotics
(15). Recent 46
epidemiological studies have reported on the widespread
emergence of a single clonal 47
group, provisionally designated clonal group A (CGA), among
TMP-SMZ-resistant 48
strains of uropathogenic E. coli (1,4,9,10,11). CGA has been
reported to account for up 49
to 50% of TMP-SMZ resistant E. coli isolates from women with
acute uncomplicated 50
cystitis and pyelonephritis (9). Recent human CGA isolates have
typically exhibited a 51
number of traits that set them apart from other uropathogenic or
drug-resistant E. coli, 52
including their characteristic virulence factor profile, several
distinctive O antigens, the 53
H18 flagellar antigen, and multidrug resistance, including to
ampicillin, chloramphenicol, 54
streptomycin, sulfonamides, tetracycline, and trimethoprim (9).
55
56
The widespread occurrence of CGA E. coli, and the occurrence in
one community 57
of a seeming point-source outbreak of UTIs due to the same
pulsotype of CGA (11), has 58
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raised questions regarding the mode of transmission of these
organisms. Recent travel to 59
areas with a high prevalence of TMP-SMZ resistant E. coli has
been previously cited as a 60
risk factor for acquiring TMP-SMZ-resistant E. coli strains
(12). This finding suggests 61
that exposure to contaminated food or water may represent a
means for the dissemination 62
of these pathogenic E. coli (10,11,14,17). The current study was
designed to assess the 63
prevalence and characteristics of TMP-SMZ resistant E. coli and
CGA in domestic 64
sewage samples collected from various locations throughout the
United States. 65
66
MATERIALS AND METHODS 67
68
Samples and primary cultures. Two sewage effluent samples
(primary and 69
secondary), prior to chlorination, were collected from each of
seven geographically 70
dispersed wastewater treatment plants in the United States: San
Jose, California (CA), 71
Tallahassee, Florida (FL), Lewiston, Maine (ME), Cincinnati,
Ohio (OH), Virginia 72
Beach, Virginia (VA), Seattle, Washington (WA), and Milwaukee,
Wisconsin (WI). 73
Samples were shipped on ice and analyzed within 24 hours of
collection. The membrane 74
filtration procedure using mFC agar (BD Bioscience, Sparks, MD)
and nutrient agar 75
containing 4-methylumbelliferyl beta-D-glucuronide (BD
Bioscience, Sparks, MD) (3) 76
was used to detect E. coli. Approximately 200 E. coli colonies
from each location were 77
picked at random and streaked for purity on heart infusion agar
(BD Bioscience, Sparks, 78
MD). 79
80
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Susceptibility testing. Isolates were sub-cultured to
Mueller-Hinton agar (BD 81
Bioscience, Sparks, MD) and screened for susceptibility to
TMP-SMZ (BD Bioscience, 82
Sparks, MD) by the disk diffusion method (13). E. coli strain
25922 (American Type 83
Culture Collection, ATCC) was used as a reference control
strain. All TMP-SMZ 84
resistant isolates (zone diameter of ≤ 10mm) were saved for
further study, as was a group 85
of TMP-SMZ susceptible E. coli isolates (which were selected as
described below as 86
controls for geographically matched comparisons). All isolates
were confirmed as E. coli 87
using the API 20E test system (bioMerieux, Marcy’Etoile,
France). Isolates were also 88
tested for susceptibility to ampicillin (AM), chloramphenicol
(CH), streptomycin (ST), 89
and tetracycline (TE) by using E-test strips (AB Biodisk, Solna,
Sweden), as directed by 90
the manufacturer, to determine minimum inhibitory concentration
(MIC) values. Isolates 91
were classified as susceptible (s), intermediate (i), or
resistant (r), based upon MIC 92
criteria as specified by the Clinical Laboratory and Standards
Insititue (CLSI) (13) or 93
based on published precedent (St) (9). The following criteria
were used for each 94
antibiotic (MIC µg/mL): AM (s = # 8, i = 16, r = ≥ 32), CH (s =
#8, i = 16, s = ≥32), ST 95
(r = ≥ 8), TE (s = # 4, i = 8, r = ≥ 16), TMP-SMZ (s = # 2, r =
≥ 4). 96
97
Molecular analysis. All TMP-SMZ-resistant isolates were O:H
serotyped by the 98
E. coli Reference Center at the Pennsylvania State University
(University Park, PA) and 99
were phylotyped (for phylogenetic groups A, B1, B2, and D) using
a multiplex PCR 100
procedure (2). All TMP-SMZ-resistant isolates and a group of 77
geographically matched 101
TMP-SMZ-susceptible isolates were tested for CGA status by using
a gene-specific PCR 102
procedure that detects a distinctive single nucleotide
polymorphism (SNP) within fumC 103
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(8). All CGA isolates and a group of geographically matched
non-CGA, TMP-SMZ-104
resistant control isolates (n = 22, chosen 2:1 with respect to
the CGA isolates with the 105
exception of CA, where there were only 18 TMP-SMZ-resistant
non-CGA isolates), were 106
tested for 40 virulence factors of extraintestinal pathogenic E.
coli by PCR as previously 107
described (7). CGA isolates were further assessed by random
amplified polymorphic 108
DNA (RAPD) analysis using arbitrary decamer primer 1254
5’-ccgcagccaa-3’ (7) in 109
comparison with CGA and non-CGA reference strains, and by
pulsed-field gel 110
electrophoresis (PFGE) analysis of XbaI-digested total DNA (11).
111
112
Statistical analysis. Comparisons of proportions were tested
using Fisher’s exact 113
test (two-tailed). The criterion for statistical significance
was P < 0.05. The BioNumerics 114
software (Applied Maths), which has band tolerance of 1.15% was
used to assess the 115
digital images of the PFGE profiles. 116
117
118
RESULTS 119
120
Distribution of TMP-SMZ resistance. A total of 1,484 arbitrarily
selected E. 121
coli sewage isolates (primary effluents n = 732, secondary
effluents n = 754) from seven 122
locations were characterized, representing approximately 200
isolates from each location 123
(Table 1). Seventy-seven (5%) of the isolates were resistant to
TMP-SMZ. The 124
prevalence of TMP-SMZ resistance varied among the various
locales, with the highest 125
values being observed in CA (13%) and WI (7%), followed by OH,
WA (5%), VA (2%), 126
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and ME (
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[40%)], P < 0.0001). Nonetheless, while 33% of the
environmental CGA isolates had 150
serotypes typical of those reported for human clinical CGA
isolates (i.e. O17,77:H18, 151
O11:H18), 67% had serotypes not previously described among human
clinical or fecal 152
CGA isolates. 153
154
Phylogenetic distribution. As expected, all 15 CGA isolates
belonged to 155
phylogenetic group D (9). In contrast the non-CGA,
TMP-SMZ-resistant isolates (n = 156
62) were approximately evenly distributed over the four
phylogenetic groups: 18 (29%) 157
group A, 15 (24%) group B1, 15 (24%) group B2, and 14 (23%)
group D. 158
159
Antimicrobial resistance profiles. The CGA isolates and the
TMP-SMZ-160
resistant non-CGA isolates differed according to their composite
resistance phenotypes. 161
Among the 15 CGA isolates, 5 resistance profiles were
encountered. One isolate 162
exhibited TMP-SMZ resistance only, 2 (13%) were resistant to 2
additional 163
antimicrobials each (AM, ST and AM, TE), 11 (73%) were resistant
to 3 additional 164
antimicrobials each (AM, ST, TE), and 1 exhibited resistance to
all 4 additional 165
antimicrobials tested (AM, CH, ST, TE). In contrast, the 62
non-CGA, TMP-SMZ-166
resistant isolates exhibited 11 different multiple antimicrobial
resistance patterns. In 167
order of descending prevalence, 25 (40%) were resistant to two
additional antimicrobials, 168
20 (32%) were resistant to three additional antimicrobials, 9
(14%) were resistant to four 169
additional antimicrobials, 7 (11%) were resistant to one
additional antimicrobial, and 1 170
(2%) was resistant only to TMP-SMZ. The four most commonly
occurring associated 171
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resistance profiles among the non-CGA, TMP-SMZ-resistant
isolates were: AM, ST, TE 172
(n = 20); AM, TE (n = 13); AM, ST (n = 8), and AM, CH, ST, TE (n
= 8). 173
174
Virulence profiles. The 15 CGA isolates were compared with 22
geographically 175
matched non-CGA TMP-SMZ-resistant isolates for virulence traits,
including alleles of 176
papA allele (P fimbriae structural subunit) (Table 2). The
non-CGA isolates were 177
selected to provide a distribution among the four phylogenetic
groups: A (n = 7), B1 (n = 178
4), B2 (n = 6), and D (n = 5). The CGA isolates were divided
between the F10 (n = 9) 179
and F16 (n = 6) papA alleles, whereas none of the non-CGA
isolates exhibited either of 180
these two papA alleles (P < 0.001 and P = 0.002,
respectively). In contrast, 3 of the non-181
CGA isolates, but none of the CGA isolates, exhibited the F12 or
F14 papA allele. 182
Additionally, all CGA isolates, but only 3 (14%) of the non-CGA
isolates, exhibited 183
papEF (P fimbriae tip pilins) (P < 0.0001). The CGA and
non-CGA isolates also differed 184
significantly (p < 0.0001) according to the prevalence of
five non-pap virulence traits, 185
including iha (adhesin/siderophore receptor), sat (secreted
autotransporter toxin), iutA 186
(aerobactin receptor), kpsM II (group II capsule), and ompT
(outer membrane protease T). 187
afa/dra (Dr-antigen binding adhesins) was the only virulence
trait which demonstrated a 188
significant negative association with CGA. 189
190
Interestingly, although all CGA isolates exhibited papEF (P
fimbriae tip pilus), 191
only six (40%) also exhibited papA, papC (P fimbriae assembly),
and papG allele II (P 192
fimbriae adhesin variant II). Moreoever, all CGA isolates
exhibiting the F10 papA allele 193
(n = 9) had papEF as their only other pap element, whereas CGA
isolates exhibiting the 194
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F16 papA alleles (n = 6) contained a complete copy of the pap
operon, including papA, 195
papC, papEF, and papG (allele II). 196
197
RAPD and PFGE analysis. The RAPD genomic profiles of the 15 CGA
isolates 198
were highly homogeneous and matched those of reference CGA
isolates UMN026 and 199
SEQ102, whereas they differed substantially from those of
non-CGA controls (Figure 1). 200
Interestingly, CGA isolates containing the F10 papA allele
typically exhibited a one-band 201
RAPD profile difference in comparison with the CGA isolates
containing the F16 papA 202
allele, consistent with these two groups possibly representing
different genomic subsets 203
within CGA (Figure 1). PFGE analysis (Fig. 2) demonstrated that
although the profiles 204
of the CGA isolates exhibited an obvious overall similarity,
each isolate (lanes 2 - 9 and 205
11 - 17) had a distinct banding pattern, indicating that despite
their considerable 206
similarity (and, in several instances, common sample of origin)
no two isolates were 207
replicates of the same clone. The presence/absence of a single
high molecular weight 208
band (Figure 2) corresponded closely with the split between the
F10 and F16 papA alleles 209
among CGA isolates. 210
211
DISCUSSION 212
213
Among E. coli isolates from wastewater effluents from seven U.S.
geographic 214
regions, the prevalence of CGA and of TMP-SMZ-resistant E. coli
varied considerably 215
by region; however, no significant difference was seen between
the isolates from primary 216
and secondary effluents. The highest percentage of CGA isolates
was from California, 217
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which had not only the highest overall prevalence of TMP-SMZ
resistance (39%), but 218
also the highest proportion of TMP-SMZ-resistant isolates
accounted for by CGA (80%). 219
It is of interest that California is a region that has
previously reported a high proportion of 220
CGA isolates (51%) among TMP-SMZ resistant clinical isolates
(11). The explanation 221
for the observed variation in prevalence of CGA and of
TMP-SMZ-resistant E. coli in 222
wastewater effluents is unknow. However, possible explanations
include differences in 223
processes between wastewater treatment plants, in population
densities at each treatment 224
plant, in the types of sewages found at each treatment plant
(industrial, agricultural, or 225
urban), and the prevalence of CGA within the host population(s)
served by each plant. 226
Variation in the prevalence of CGA among clinical isolates from
different regions has 227
been documented (7, 9); it is possible that regional variation
exists also among 228
environmental samples. 229
230
The increasing occurrence of TMP-SMZ-resistant uropathogenic E.
coli 231
emphasizes the need to determine resistance prevalence levels
within a community. 232
Determining the prevalence of antimicrobial resistance in a
given locale may require 233
information beyond that obtained in clinical laboratory studies.
Data on resistance rates 234
collected only from patients with UTIs may not reflect the true
prevalence of resistance in 235
the local community (6,19), since specimens are often submitted
for culture and antibiotic 236
susceptibility testing only after initial antimicrobial therapy
has failed or because the 237
patient has had recurrent episodes of UTIs, or is otherwise
considered at risk for having a 238
resistant organism. The intestinal tract serves as the primary
source for uropathogenic E. 239
coli (6). E. coli found in domestic sewage comes predominantly
from human fecal 240
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material (18). Thus, sewage isolates may serve as
representatives of the strains of E. coli 241
which would be present within the human population in a given
locale. Surveillance of 242
antibiotic resistance in coliforms from sewage has been
previously suggested as a means 243
of monitoring changes in antibiotic resistance patterns in the
general population (18). 244
Seneviratne and Woods (1976) specifically proposed that such a
surveillance program 245
would be helpful in providing therapeutic guidance for the
treatment of urinary 246
pathogens. The results of the present study suggest that such
monitoring programs may 247
also provide useful information on the occurrence and
dissemination of specific clonal 248
groups within a given community. 249
250
Fifteen (19.5%) of TMP-SMZ-resistant isolates in this study
belonged to CGA. 251
This value is very similar to that reported in a recent national
survey of clinical isolates, 252
where CGA accounted for 15% of TMP-SMZ-resistant isolates from
diverse locales 253
across the United States (9). Among the sewage-source isolates,
CGA E. coli were 254
distinct from geographically matched non-CGA TMP-SMZ-resistant
E. coli according to 255
a broad range of bacterial characteristics, as previously
reported among human clinical 256
isolates of CGA versus non-CGA E. coli (11). 257
258
Notwithstanding the overall similarity of the present
sewage-source CGA isolates 259
to previously described human CGA isolates, some differences
were apparent. The 260
environmental isolates exhibited a broader range of serogroups
(O15, O44, O86) beyond 261
the O11, O17, O73, and O77 serogroups typically associated with
clinical CGA isolates, 262
a lower prevalence of chloramphenicol resistance (7%, vs. >
25% among clinical CGA 263
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isolates), and the unique occurrence of the F10 papA allele (60%
vs. 0%) (9). It is of 264
interest that the F10-positive isolates lacked most of the rest
of the pap operon, so 265
presumably could not express P fimbriae, which should make them
less able to colonize 266
or infect humans. Whether the F10-positive subgroup represents
an environmentally 267
adapted variant of CGA, or perhaps an ancestral precursor,
remains to be established. The 268
detection of this interesting subgroup in multiple locales
suggests it is not an isolated 269
entity, but may be broadly prevalent in sewage effluents across
the US. These findings 270
raise interesting questions regarding the ecology of these
organisms outside of the human 271
host. 272
273
In summary, the sewage CGA E. coli isolates exhibited a wider
diversity of 274
resistance profiles and somatic antigens than found in most
previous characterizations of 275
this clonal group (France et al. 2005). However, some of these
isolates had virulence 276
factor and antimicrobial resistance profiles typical of
human-source CGA isolates. This is 277
the first report of the recovery of CGA E. coli with typical
“human” pattern virulence and 278
resistance profiles from outside the human host. The presence of
CGA E. coli in sewage 279
effluents may provide a means for dissemination of this clonal
group in the environment. 280
Sewage could serve as a vehicle for entering human and non-human
hosts by direct 281
contact or through contamination of drinking water supplies.
282
283
Any opinions expressed in this paper are those of the author(s)
and do not, 284
necessarily, reflect the official positions and policies of the
USEPA. Any mention of 285
products or trade names does not constitute recommendation for
use by the USEPA. 286
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Acknowledgments 288
289
This material is based on work supported by the Office of
Research and Development, 290
Medical Research Service, Department of Veterans Affairs (JRJ).
Dave Prentiss 291
(Minneapolis VA Medical Center) prepared the figures. 292
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Table 1. Occurrence of TMP-SMZ resistance and Escherichia coli
clonal group A 374
(CGA) among 1,484 E. coli sewage isolates from seven regions.
375
Region Total E. coli
isolated, no.
aTMP-SMZ-resistant
E. coli, no. (% of total)
CGA E. coli, no.
(% of TMP-SMZ-
resistant)a
San Jose, CA 226 30 (13) 12 (40)
Tallahassee, FL 210 5 (2) 0 (
-
Table 2. Virulence factor profiles among clonal group A (CGA)
and non-CGA 384
Escherichia coli sewage isolates. 385
386
Prevalence of associated trait, no (%)
Trait+
CGA
(n = 15)
non-CGA++
(n = 22)
p +++
value
F10 papA allele
9 (60) 0 (0) < 0.0001
F16 papA allele 6 (40) 0 (0) 0.0022
papEF 15 (100) 3 (14) < 0.0001
papG allele II 6 (40) 1 (4) 0.0113
afa/dra 0 (0) 14 (64) (< 0.0001)
iha 14 (93) 3 (14) < 0.0001
sat 14 (93) 4 (18) < 0.0001
iutA 14 (93) 7 (32) 0.0002
kpsM II 15 (100) 10 (45) 0.0004
ompT 15 (100) 8 (36) < 0.0001
+ Only those traits for which prevalence differences between CGA
vs. non-CGA isolates 387
were statistically significant (Fisher’s exact test, p <
0.05) are shown. 388
Trait definitions: papA (P fimbriae structural subunit) 389
papEF (P fimbriae tip pilus) 390
papG allele II (P fimbriae adhesion variant II) 391
afa/dra (Dr-antigen binding adhesins) 392
iha (adhesin/siderophore) 393
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sat (secreted autotransporter toxin) 394
iutA (aerobactin receptor) 395
kpsM II (group II capsule) 396
ompT (outer membrane protease T) 397
398
Other traits present in CGA, but not significantly different in
overall prevalence 399
compared with non-CGA isolates, included: papC (P fimbriae
assembly), fimH (type 1 400
fimbriae adhesin), fyuA (yersiniabactin receptor), and traT
(serum resistance associated). 401
Traits absent from CGA isolates, but detected among non-CGA
isolate, included: F12 402
papA, papG allele III, iroN, K1 kpsM II variant, usp, iss, and
malX; however these 403
differences (CGA versus non-CGA) were not statistically
significantly by the Fisher’s 404
exact test. 405
++ Non-CGA TMP-SMZ-resistant control isolates were chosen in a
2:1 ratio to the CGA 406
isolates within each locale with the exception of San Jose, CA,
where only 18 non-CGA 407
TMP-SMZ resistant isolates were recovered, all of which were
used as controls. 408
+++ p value in parenthesis is for negative associations with CGA
409 AC
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410
Figure 1. Random amplified DNA (RAPD) profiles of selected
Escherichia coli 411
isolates. Lane numbers are shown below gel image. Lanes 4 and
17, 250-bp marker (M). 412
Lanes 1-3 and 5-16: clonal group A (CGA)-positive sewage
isolates. Lanes 18-19: CGA-413
positive controls (human cystitis isolates SEQ102 and UMN026,
respectively). Lanes 20-414
24: CGA-negative controls (lanes 20-21, non-CGA sewage isolates
[from phylogenetic 415
groups B2 and D, respectively]; lane 22, strain CFT073 [from
group B2]; lanes 23-24, 416
human source non-CGA isolates [from groups D and B2,
respectively]). Bullets above 417
lanes indicate CGA isolates that exhibit the consensus
CGA-associated virulence profile, 418
including the F16 papA (P fimbriae structural subunit) allele,
and characteristic CGA-419
associated RAPD profile. CGA isolates in lanes without a bullet
exhibit an atypical 420
virulence profile that includes the F10 papA allele, plus
(excepting for strain 492: lane 5) 421
an atypical RAPD profile that includes an extra ~2000 bp band
(vertical arrows, or "*" 422
for strain 492, lane 5). The profiles of all the CGA isolates
are indistinguishable (within 423
the reproducibility limits of RAPD analysis) excepting for the
~2000 bp band, and 424
collectively are distinct from the profiles of the non-CGA
isolates, each of which is 425
unique. 426
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427
428
429
Figure 2. XbaI pulsed-field gel electrophoresis (PFGE) profiles
of selected 430
Escherichia coli isolates. Lane numbers are shown below gel
image. Lanes 1, 10, and 431
18: marker (M) lanes, with E. coli O157:H7 strain G5244. Lanes
2-9 and 11-17: CGA-432
positive sewage isolates. Bullets above lanes indicate CGA
isolates that exhibit the 433
consensus CGA-associated virulence profile, including the F16
papA (P fimbriae 434
structural subunit) allele. CGA isolates in lanes without a
bullet exhibit an atypical 435
virulence profile that includes the F10 papA allele, and
(excepting for strain 518: lane 8) 436
exhibit an extra large band in the PFGE profile (vertical
arrows, or "*" for strain 518). 437
The profiles of the CGA isolates are all unique, yet they
exhibit similarities that 438
distinguish them as a group from the E. coli O157:H7 reference
strain (lanes 1, 10, 18). 439
440
441
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442
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