ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Jan. 2009, p. 292–294
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Vol. 53, No. 1
KPC-2-Producing Enterobacter cloacae and Pseudomonas putida
Coinfection in a Liver Transplant Recipient?
Jason W. Bennett,1Monica L. Herrera,2James S. Lewis II,3,5
Brian W. Wickes,3and James H. Jorgensen2,3,4*
San Antonio Military Medical Center, Fort Sam Houston, Texas 782341; Departments of Microbiology,2Medicine,3and
Pathology,4University of Texas Health Science Center, San Antonio, Texas 78229; and
Pharmacy Department, University Health System, San Antonio, Texas 782295
Received 14 July 2008/Returned for modification 10 September 2008/Accepted 1 October 2008
Carbapenemases are among the newest resistance mechanisms to emerge in some gram-negative bacteria.
We describe bacteremia in a critically ill liver transplant recipient infected with KPC-2-producing Enterobacter
cloacae and Pseudomonas putida. Although this enzyme has been previously described in Enterobacter spp., this
is the first report of KPC carbapenemase in P. putida.
Carbapenems are the broadest-spectrum ?-lactam antibiotics
and retain activity against many antibiotic-resistant organisms
to include gram-negative organisms that produce extended-
spectrum or AmpC ?-lactamases (11). However, reports of
carbapenem-hydrolyzing enzymes have become increasingly
frequent in some locations in recent years (5). In the United
States, the most common carbapenemases to emerge have
been the Klebsiella pneumoniae carbapenemases (KPCs) (5).
Since the first report of this plasmid-mediated carbapenemase
in North Carolina, several outbreaks caused by KPC-producing
isolates have been documented elsewhere, in particular in the
northeastern United States (5, 11). KPC-producing isolates
have also emerged in states outside of the northeastern United
States to include Arkansas, Michigan, Missouri, Ohio, and
Pennsylvania (12, 13). Clinical microbiology laboratories are
becoming increasingly aware of the emergence of carbapen-
emase-producing organisms, but identification of such isolates
remains difficult (2). In 2008, the Clinical and Laboratory Stan-
dards Institute (CLSI) suggested that KPC-producing isolates
may display elevated carbapenem MICs of 2 or 4 ?g/ml (6).
Although these isolates are still considered “susceptible” based
upon current CLSI interpretive criteria, they may not respond
to carbapenem therapy (6). At present, the CLSI has not rec-
ommended a phenotypic test to confirm KPC production. We
describe here simultaneous infection with KPC-2-producing
Enterobacter cloacae and Pseudomonas putida in a critically ill
liver transplant recipient.
A 54-year-old female was admitted to University Hospital to
undergo an orthotopic liver transplant from an unrelated do-
nor. Immediately after surgery, she required emergent surgical
exploration due to hemorrhage. She experienced a compli-
cated hospital course, including acute renal failure requiring
hemodialysis, pulmonary embolus, and right lobe liver infarct.
She had an open postsurgical abdominal wound following bil-
iary anastamosis, right hepatic lobectomy, and repair of jejuno-
jejunostomy. Due to a persistently elevated white blood cell
count and the frequent need for vasopressor support, she
received prolonged courses of broad-spectrum antibiotics to
include 5 weeks of empirical meropenem and 7 weeks of
linezolid. She also received trimethoprim-sulfamethoxazole,
valgancyclovir, and antifungal prophylaxis throughout her
hospital course in accordance with the local transplant pro-
On hospital day 45, multidrug-resistant E. cloacae and P.
putida with similar antibiotic susceptibility profiles grew from
multiple blood cultures (Table 1). Both isolates were suscep-
tible to amikacin, and the patient was treated with that agent.
Ciprofloxacin was added to the antibiotic regimen to broaden
coverage; the E. cloacae demonstrated only intermediate sus-
ceptibility to this antimicrobial agent. The colistin MIC for the
P. putida was 2 ?g/ml, but for E. cloacae the MIC was ?16
?g/ml based upon CLSI reference broth microdilution testing
(7). The CLSI does not have specific colistin breakpoints for
the Enterobacteriaceae or for P. putida, but a colistin MIC of
?2 ?g/ml is considered susceptible for P. aeruginosa and Acin-
etobacter spp., and a colistin MIC of ?16 ?g/ml would be
considered resistant for both organisms (6). Subsequent to
obtaining these blood isolates, both of these organisms grew
from tissue cultures obtained during debridement of sacral and
abdominal wounds. Proteus mirabilis, Stenotrophomonas mal-
tophilia, and Escherichia coli were also isolated from the same
wound cultures. Despite aggressive broad-spectrum antimicro-
bial therapy, the patient died 12 days after her first episode of
The E. cloacae and P. putida isolates were both initially
identified using a Vitek 2 instrument (bioMe ´rieux, Hazelwood,
MO). The identifications were confirmed by performing 16S
rRNA sequencing (15). Because of resistance to meropenem
and to all other ?-lactams tested, both isolates were screened
for the presence of a carbapenemase using the modified Hodge
test (2). Both strains demonstrated carbapenem hydrolysis us-
ing imipenem as the test substrate (Fig. 1). PCR amplification
of DNA extracts using previously described primers and test
conditions for various extended-spectrum ?-lactamases and
KPCs were performed, followed by sequencing of the PCR
* Corresponding author. Mailing address: Department of Pathology,
University of Texas Health Science Center, 7703 Floyd Curl Drive, San
Antonio, TX 78229-3900. Phone: (210) 567-4088. Fax: (210) 567-2367.
?Published ahead of print on 13 October 2008.
products (9, 12). This revealed the presence of blaKPC-2in both
isolates and blaSHV-12in the E. cloacae.
Our patient suffered from bacteremia due to KPC-2-produc-
ing E. cloacae and P. putida recovered simultaneously from
multiple cultures, and she eventually died. Although the initial
source of infection was undetermined, both organisms were
isolated from wound cultures as well as from blood. It is pos-
sible that transfer of the plasmid encoding the carbapenemase
could have occurred in the milieu of the mixed wound infec-
tion. Prior to this patient’s infection, no KPC-producing iso-
lates had been recovered in this hospital, and no others have
been detected since this case.
In the United States, KPC enzymes have emerged as a major
clinical concern among some members of the Enterobacteria-
ceae, but these enzymes have rarely been described outside of
that family (5, 11). Recently, three Pseudomonas aeruginosa
clinical isolates from Colombia were found to express KPC-2;
however, we believe that the present study represents the first
report of KPC production in P. putida (14). Infections caused
by P. putida are relatively rare and are generally restricted to
immunocompromised patients and patients with invasive med-
ical devices in place (4). Although not previously recognized to
produce KPC, this member of the fluorescent group of pseudo-
monads is often resistant to fluoroquinolones, aminoglyco-
sides, and various ?-lactams (1, 3, 8, 10). Previously described
carbapenem-resistant P. putida isolates have been associated
with production of IMP- or VIM-type metallo-?-lactamases,
but not KPCs (1, 3, 8, 10).
Nonsusceptibility to colistin has been described among the
Enterobacteriaceae. (5). When present in combination with a
carbapenemase, therapeutic options are extremely limited. It is
particularly unusual that this isolate was nonsusceptible given
that this patient had not been exposed to colistin during her
hospital course. Susceptibility to colistin should not be as-
sumed, and appropriate testing should be performed when
therapy with this potentially toxic antimicrobial agent is con-
These appear to represent the first KPC-producing clinical
isolates in Texas, as well as the first occurrence of blaKPC-2in
P. putida. This extends the host range for the KPC-2 ?-lacta-
mase into another Pseudomonas species. Microbiologists and
clinicians should be aware that carbapenemases can appear in
several different species and in different gram-negative bacte-
rial families. Practical phenotypic screening and confirmatory
tests are needed to facilitate the timely detection of such
strains by clinical microbiology laboratories.
The opinions or assertions contained herein are the private views of
the authors and are not to be construed as official or reflecting the
views of the Department of Defense or the U.S. government.
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TABLE 1. Antimicrobial agent susceptibilities of two clinical
Antimicrobial MIC (?g/ml) for:
E. cloacaeP. putida
abla enzymes detected: E. cloacae, KPC-2 and SHV-12; and P. putida, KPC-2.
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294 BENNETT ET AL.ANTIMICROB. AGENTS CHEMOTHER.