Advances in Infectious Diseases, 2013, 3, 50-54
http://dx.doi.org/10.4236/aid.2013.31006 Published Online March 2013 (http://www.scirp.org/journal/aid)
Microbiologic and Clinical Comparison of Patients
Harboring Escherichia coli Blood Isolates with and without
Extended-Spectrum β-Lactamases
Anna Nussbaum1, Noriel Mariano1, Rita Colon-Urban2, Rachelle A. Modeste2, Sadia Zahid1,
Wehbeh Wehbeh1, Sorana-Segal-Maurer1, Carl Urban1*
1Infectious Disease Section, New York Hospital Queens, New York, USA; 2State University of New York College at Old Westbury,
New York, USA.
Received December 14th, 2012; revised January 16th, 2013; accepted February 18th, 2013
ABSTRACT
The clinical and microbiologic characteristics of 34 patients with extended-spectrum β-lactamase (ESBL) positive E.
coli isolated from blood were compared to 66 bacteremic patients with ESBL negative E. coli, from January 2007
through December 2009. Of the 21 ESBL positive isolates available for PCR analysis, 13 were positive for CTX-M, 8
for TEM, 4 for SHV β-lactamases, with 6 possessing multiple enzymes. Twenty of 34 (59%) ESBL-positive and 41 of
66 (62%) ESBL-negative blood isolates were considered community-associated. All but one isolate in both groups had
MICs of ≤1.0 µg/ml to meropenem. However, when compared to ESBL-negative isolates, ESBL-positive isolates were
more frequently resistant to levofloxacin, trimethoprim/sulfamethoxazole and had higher MICs to gentamicin, tobramy-
cin and piperacillin/tazobactam. The use of intravenous and urinary catheters was strongly associated with the isolation
of E. coli bloodstream isolates in both groups of patients. Although hospital stay was similar in both groups, appropriate
therapy was given in 87% of patients with ESBL positive vs. 98% of patients with ESBL negative isolates and mortality
was greater for patients with ESBL positive isolates (26% vs. 17%). Since a large proportion of E. coli blood isolates
were ESBL-positive and community-associated, carbapenems should be considered as initial empiric therapy for such
infections in our locale.
Keywords: Escherichia coli Bacteremia; Extended-Spectrum β-Lactamases
1. Introduction
Escherichia coli harboring extended spectrum β-lac-
tamases (ESBLs) has emerged as a global threat [1,2].
Organisms with these enzymes have been isolated from a
multitude of sources including patients associated with
healthcare settings, the community, foods, companion
and non-companion animals [1]. While E. coli blood-
stream infections were traditionally treated with late
generation cephalosporins, increased identification of
ESBL positive isolates has led to therapeutic dilemmas
since such isolates often contain plasmid carrying genes
which confer resistance to additional classes of antimi-
crobials [1,3]. E. coli possessing CTX-M β-lactamases
are a relatively new type of ESBL which we and others
have recently identified among hospitalized patients,
residents of long-term care facilities, pediatric patients,
and patients from the community, predominantly from
urinary tract isolates [1,4-6]. This retrospective investi-
gation was conducted to determine if such isolates are
present in patients with bacteremia in our setting. By
comparing ESBL-positive and -negative E. coli blood-
stream isolates, we sought to classify ESBLs and identify
characteristics such as community association, antibiotic
susceptibility, factors for acquisition, antibacterial ther-
apy and outcomes of patients in both groups.
2. Materials and Methods
2.1. Study Population
From January 1, 2007 through December 31, 2009, E.
coli blood isolates were identified and obtained from the
clinical microbiology laboratory at New York Hospital
Queens (NYHQ). ESBL-positive E. coli were identified
using BD Phoenix™ NMIC/ID-123 panels (Becton, Dic-
kinson and Company, Sparks, MD). Comparison cohort
of patients with ESBL-negative bloodstream isolates was
matched by age and gender.
*Corresponding author.

Microbiologic and Clinical Comparison of Patients Harboring Escherichia coli Blood Isolates with and
without Extended-Spectrum β-Lactamases
51
2.2. Clinical Data Collection
This investigation was conducted as a quality improve-
ment project and did not require IRB approval. Patients’
charts were reviewed for demographic information in-
cluding age, gender, previous exposure to healthcare
settings, prior hospital admission by history, antimi-
crobial treatment within the past year and pre-existing
comorbidities. Bloodstream infections were defined as
community-associated when isolated from non-hospital-
ized patients receiving no antibiotics and not having any
healthcare contact within the previous 30 days. Risk
factors for acquisition included presence of urinary ca-
theters, intravenous catheters, feeding tubes, endotra-
cheal tubes, previous antimicrobial use, presence of E.
coli in urine, nursing home residency and previous hos-
pital admission within the last year. P-values were calcu-
lated using Excel Microsoft 2010 software. Antimicro-
bial treatment including antimicrobial therapy, dosage,
length of therapy and in-hospital mortality was also col-
lected from medical records. Appropriate therapy was
defined as treatment with an antibacterial to which the
organism was susceptible.
2.3. Microbiology Procedures
Minimim inhibitory concentrations (MICs) for ceftria-
xone, ceftazidime, cefepime, piperacillin/tazobactam, tri-
methoprim/sulfamethoxazole, levofloxacin, gentamicin,
amikacin, tobramycin, and meropenem were obtained
and recorded for 31 ESBL positive and 54 ESBL nega-
tive E. coli isolates from antibiograms generated in the
clinical microbiology laboratory using the using BD
Phoenix™ NMIC/ID-123 panels (Becton, Dickinson and
Company, Sparks, MD). Polymerase chain reaction (PCR)
analysis was performed using primers for the CTX-M-1
group and CTX-M-15, as previously described [4]. Pri-
mers for TEM and SHV enzymes were used as de-
scribed in [7].
3. Results
34 ESBL-positive and 66 ESBL-negative E. coli blood,
single patient isolates, were identified from hospitalized
patients during the study period. Of 34 ESBL-positive
isolates, 20 (59%) and 41 (62%) of ESBL-negative iso-
lates were considered as community-associated. The re-
maining patients in both groups were from long-term
care facilities or coming from home with additional risk
factors for acquisition. Of the 21 ESBL positive isolates
available for PCR analysis, 13 were positive for CTX-M,
8 for TEM and 4 for SHV β-lactamases. 10 of the CTX-
M positive isolates were identified as CTX-M-15. Six
isolates possessed two or more classes of β-lactamases
and 4 isolates were PCR negative for TEM, SHV and
CTX-M enzymes. The majority of ESBL-positive iso-
lates was also resistant to levofloxacin, trimethoprim/
sulfamethoxazole and possessed higher MICs to gen-
tamicin, tobramycin and piperacillin/tazobactam when
compared to ESBL-negative isolates. All but one ESBL-
positive isolate had MICs ≤1.0 µg/ml to meropenem
(Table 1). A similar percentage of ESBL-positive and
ESBL-negative E. coli isolates in patients were over the
age of 65 (mean ages = 70.9 and 71.5 years, respectively),
were female, and resided in nursing homes (Table 2).
These findings were in accord with those of other studies
[8-11]. Patients with venous and urinary catheters were
risk factors associated with isolation of E. coli from the
Table 1. Antimicrobial susceptibility of E. coli isolates from blood.
ESBL Positive (n = 31) ESBL Negative (n = 54)
Antimicrobial Agent MIC50 MIC90 MIC RANGE MIC50 MIC90 MIC RANGE
Amikacin ≤8 ≤8 ≤8 -16 ≤8 ≤8 ≤8
Cefepime 8 >16 ≤1 - >16 ≤1 ≤1 ≤1
Ceftazidime 16 >16 1 - >16 ≤0.5 ≤0.5 ≤0.5
Ceftriaxone >32 >32 ≤2 - >32 ≤2 ≤2 ≤2 - 32
Gentamicin ≤2 >8 ≤2 - >8 ≤2 >8 ≤2 - >8
Levofloxacin >4 >4 ≤1 - >4 ≤1 >4 ≤1 - >4
Meropenem ≤1 ≤1 ≤1 - 2 ≤1 ≤1 ≤1
Piperacillin/tazobactam 8/4 >64/4 ≤2/4 - >64/4 ≤2/4 ≤4/4 ≤2/4 - 64/4
Tobramycin 8 >8 ≤2 - >8 ≤2 >8 ≤2 - >8
Trimethoprim/sulfamethoxazole >2/38 >2/38 ≤0.5/9.5 - 2/38 ≤0.5/9.5 >2/38 ≤0.5/9.5 - >2/38

Microbiologic and Clinical Comparison of Patients Harboring Escherichia coli Blood Isolates with and
without Extended-Spectrum β-Lactamases
52
Table 2. Comparison of risk factors for patients with ESBL-
positive and ESBL-negative E. coli.
Risk Factor ESBL positive
(n = 34)
ESBL negative
(n = 66) p-value
Age >65 21 (62) 45 (68) 0.41
Female 15 (44) 28 (42) 0.87
Nursing home residency 9 (26) 20 (30) 0.69
Previous hospital admission
(<1 year) 15 (44) 23 (35) 0.37
Previous antimicrobial use
(<1 year) 10 (29) 18 (31)* 0.91
Urinary catheter use 29 (85) 42 (69)** 0.08
Venous catheter use 24 (71) 26 (40) 0.001
Feeding tube use 11 (32) 17 (26) 0.32
Endotracheal tube use 12 (35) 16 (24) 0.24
E. coli presence in urine 16 (47) 39 (59) 0.16
Neutropenia 5 (15) 7 (11) 0.55
Diabetes mellitus 12 (35) 22 (39)*** 0.76
*n = 59, **n = 61, ***n = 57.
blood for both groups of patients. E. coli was also iso-
lated from the urine in 47% and 59% of patients with
ESBL-positive and ESBL-negative blood isolates, re-
spectively (Table 3). In addition, one ESBL CTX-M-15
positive blood isolate was obtained from an 18 month-
old female patient.
Finally, the majority of bacteremic patients with ESBL-
positive isolates (61%) in our study, received meropenem
alone or in combination with an aminoglycoside as initial
therapy. 13% of these patients did not receive appropriate
empiric or definitive antibiotics (Table 3). In addition,
19% of patients with ESBL positive isolates received ce-
fepime and 45% piperacillin/tazobactam to which the or-
ganisms were not susceptible (Table 3). Treatment data
was not available for three patients with ESBL-positive
isolates and eleven patients with ESBL-negative isolates.
Despite similar mean and median length of stays in both
groups of patients, patients presenting with ESBL-positive
E. coli had a greater in-hospital mortality rate.
4. Discussion
We and others have previously documented CTX-M en-
zymes in patients from hospitals, associated long-term
care facilities, community-associated, and the pediatric
population which were predominantly from urinary tract
isolates [4-6,9]. This study records the preponderance of
such enzymes, most notably CTX-M-15, in blood iso-
lates from hospitalized and community-onset patients
which was similar to the findings of others [9,12]. Our
Table 3. Mortality, length of stay, treatment and outcomes
of bacteremic patients with ESBL-positive and ESBL-ne-
gative E. coli isolates.
Outcome/Treatment
ESBL positive
(n = 31 for
treatment data)
ESBL negative
(n = 55 for
treatment data)
In-hospital mortality 9 (26%) 11 (17%)
Mean length of stay (in days)13.2 (1 to 39) 13.7 (1 to 71)
Median length of stay (in days)12.5 (1 to 39) 11 (1 to 71)
Treatment with amikacin 5 (16) 2 (4)
Treatment with cefepime 6 (19) 11 (20)
Treatment with ceftazidime0 (0) 0 (0)
Treatment with ceftriaxone0 (0) 4 (7)
Treatment with gentamicin16 (52) 23 (42)
Treatment with levofloxacin17 (55) 39 (71)
Treatment with meropenem19 (61) 17 (31)
Treatment with
piperacillin/tazobactam 14 (45) 35 (64)
Treatment with tobramycin0 (0) 0 (0)
Treatment with
trimethoprim/sulfamethoxazole 3 (10) 2 (4)
Appropriate therapy 27 (87) 54 (98)
study also revealed that many risk factors associated with
patients in whom ESBL-positive and ESBL-negative E.
coli were isolated from blood were similar, with the ex-
ception of venous catheter use which was more common
in bacteremic patients with ESBL-positive isolates (Ta-
ble 3). Other investigations have also reported such re-
sults [9,10].
An additional and significant finding was the isolation
of a CTX-M-15 harboring E. coli from the blood in an 18
month-old patient and may be a growing trend in this
previously under recognized population [6,13]. We have
recently reported an increase in community-associated
ESBL-positive urine cultures from pediatric patients in
our area and mentioned the possibility of progression to
more serious disease [6,14]. The presence of ESBL-
positive E. coli blood isolates in the pediatric population
is of great concern and continued surveillance is war-
ranted [13].
An understanding of the risk factors associated with
ESBL-producing E. coli bloodstream infections and local
antibiotic susceptibility patterns might lead to admini-
stration of appropriate initial antibacterial therapy since
poorer outcomes might be expected [15]. Although one
investigation documented the use of carbapenem and
β-lactam/β-lactamase inhibitor combination therapy to
decrease mortality in bloodstream infections with ESBL

Microbiologic and Clinical Comparison of Patients Harboring Escherichia coli Blood Isolates with and
without Extended-Spectrum β-Lactamases
53
producing isolates, other studies have not supported this
[9,15,16]. Additional studies have shown that increased
mortality was not statistically associated with ESBL pro-
duction or inappropriate therapy [10,12,16]. Differences
in outcome studies can be explained by associated vari-
ables including severity of illness of patients, comorbid
conditions, time to initiation of antibiotics, and virulence
factors associated with the organisms and may be inde-
pendent of ESBL production [10,12,16,17]. While physi-
cians should avoid broad-spectrum empiric therapy, con-
tinued surveillance and administration of carbapenems
should be considered as empiric therapy for patients with
bloodstream infections due to suspected ESBL positive E.
coli in our community [18].
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