Subido por Manuel Perez Gomez

Kang C. CEFEPIME AND TGHE INOCULUM EFFECT IN TEST WITH KP

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JAC
Journal of Antimicrobial Chemotherapy (2004) 54, 1130–1133
DOI: 10.1093/jac/dkh462
Advance Access publication 14 October 2004
Cefepime and the inoculum effect in tests with
Klebsiella pneumoniae producing plasmid-mediated
AmpC-type b-lactamase
Cheol-In Kang1, Hyunjoo Pai2, Sung-Han Kim1, Hong-Bin Kim1, Eui-Chong Kim3,4,
Departments of 1Internal Medicine and 3Laboratory Medicine, Seoul National University College of Medicine,
Seoul; 2Department of Internal Medicine, Hanyang University College of Medicine, Seoul;
4
Clinical Research Institute, Seoul National University Hospital, Seoul, Republic of Korea
Received 10 July 2004; returned 19 August 2004; revised 5 September 2004; accepted 14 September 2004
Objective: In the past decade, a new problem in Klebsiella pneumoniae strains has emerged: plasmidmediated AmpC enzymes. This study was conducted to investigate the activity of cefepime against
clinical isolates by determining the activities of cefepime and three other parenteral b-lactam agents in
standard and high inoculum MIC tests.
Methods: A total of 61 K. pneumoniae blood isolates, including 28 isolates producing AmpC-type
b-lactamases (14 isolates of DHA-1 and 14 isolates of CMY-1-like) and 33 isolates producing
extended-spectrum b-lactamases (ESBLs) (32 isolates of TEM- or SHV-related and one isolate of
CTX-M-14-like), were included in the study. Antimicrobial susceptibilities were determined using
broth microdilution MIC tests with standard and 100-fold-higher inocula. The inoculum effect was
defined as an eight-fold or greater MIC increase on testing with the higher inoculum.
Results: In tests with AmpC b-lactamase-producing K. pneumoniae isolates and their transconjugants,
the inoculum effect was most consistently detected with cefepime, cefotaxime and ceftazidime, as
inoculum effects were consistently detected in ESBL-producing isolates. However, the inoculum effect
was least frequently detected with imipenem.
Conclusion: Although the inoculum effect is an in vitro laboratory phenomenon, these results suggest
that cefepime may be a less than reliable agent for therapy in cases of high inoculum infections caused
by AmpC b-lactamase-producing K. pneumoniae.
Keywords: K. pneumoniae, cephalosporins, b-lactam resistance
Introduction
In the past decade, a new problem in Klebsiella pneumoniae
strains has emerged: plasmid-mediated AmpC enzymes. They
are derived from the chromosomal AmpC genes of Gramnegative organisms, such as Citrobacter freundii, Enterobacter
cloacae and Aeromonas species.1 Strains with plasmid-mediated
AmpC enzymes are generally resistant to broad-spectrum penicillins, extended-spectrum cephalosporins and cephamycins.
These strains are also resistant to aztreonam, but susceptible to
cefepime, cefpirome and carbapenems.1 Previous studies, based
on antimicrobial susceptibility data, suggested that cefepime
might be effective for the treatment of infections caused by
AmpC-producing K. pneumoniae.2,3
In vitro studies with high inocula show that the MICs of
cefepime for extended-spectrum b-lactamase (ESBL)producing isolates of K. pneumoniae and Escherichia coli are
often greatly elevated, suggesting that these agents are inactivated by ESBLs.4,5 Indeed, there are reports on cefepime failure in serious infections caused by ESBL producers.6
Similarly, in serious infections caused by AmpC b-lactamaseproducing K. pneumoniae, it has been proposed that a major
..........................................................................................................................................................................................................................................................................................................................................................................................................................
*Correspondence address. Department of Internal Medicine, Seoul National University College of Medicine, 28 Yongon-dong Chongno-gu,
Seoul 110–744, Republic of Korea. Tel: +82-2-760-2945; Fax: +82-2-762-9662; E-mail: mdohmd@snu.ac.kr
..........................................................................................................................................................................................................................................................................................................................................................................................................................
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Myoung-don Oh1,4* and Kang-Won Choe1,4
C-I. Kang et al.
inoculum effect for an antimicrobial agent precludes its use.7
Thus, this study was designed to further investigate the
activity of cefepime against clinical isolates by determining
the activities of this agent and three other parenteral b-lactam
agents in standard and high inoculum MIC tests.
Materials and methods
Bacterial strains and the characterization of b-lactamases
Antimicrobial susceptibility tests and the inoculum effect
Antimicrobial susceptibilities were determined using a broth microdilution MIC method using inocula that differed 100-fold in density. The inocula comprised 105 (the standard inoculum) and 107
(the higher inoculum) cfu/mL suspended in Mueller – Hinton broth
(Becton Dickinson, Sparks, MD, USA). Standard inoculum tests
were conducted according to the National Committee for Clinical
Laboratory Standards.9 An inoculum effect was defined as an
eight-fold or greater increase in MIC on testing with the higher
inoculum.4 Antimicrobials tested were cefotaxime (C.J. Corp. Pharmaceutical Division, Seoul, Korea), ceftazidime (Hanmi Pharmaceutical Co., Ltd., Seoul, Korea), cefepime (Boryung Pharm.,
Seoul, Korea) and imipenem (Choongwae Pharma Corp., Seoul,
Korea).
Inoculum effects in antimicrobial susceptibility tests
with ESBL-producing K. pneumoniae isolates
A total of 33 K. pneumoniae isolates, 32 isolates producing
TEM- or SHV-related ESBLs and one isolate producing
a CTX-M-14-like enzyme, were tested. Cefotaxime, ceftazidime and cefepime were found to be associated with inoculum effects in 100% of evaluable tests of ESBL-producing
K. pneumoniae isolates (i.e. excluding those which could not
be evaluated because of off-scale MICs) (Table 1). The
MIC50 of cefepime was 8 mg/L in standard inoculum tests
and >256 mg/L in higher inoculum tests. However, imipenem
inhibited all isolates at a concentration of 0.5 mg/L in standard inoculum tests and also inhibited all isolates at 4 mg/L
in higher inoculum tests.
Inoculum effects in antimicrobial susceptibility tests with
AmpC b-lactamase-producing K. pneumoniae isolates
Fourteen isolates producing DHA-1-related b-lactamases and
14 isolates producing CMY-1-like enzyme were tested. As
inoculum effects were consistently detected in ESBL-producing
strains, cefotaxime, ceftazidime and cefepime were also associated with inoculum effects in 100% of evaluable tests with
AmpC b-lactamase-producing K. pneumoniae isolates (i.e.
excluding those which could not be evaluated because of offscale MICs) (Table 2). The MIC50 of cefepime was 1 mg/L in
the standard inoculum tests and >256 mg/L in the higher
inoculum tests. However, imipenem at 0.5 and 8 mg/L inhibited all isolates in standard and higher inoculum tests,
respectively.
For DHA-1-related AmpC-producing K. pneumoniae isolates,
the MICs of antibiotics by the standard and higher inoculum
tests are shown in Table 2. In addition, for CMY-1-like AmpCproducing K. pneumoniae isolates, the MICs of antibiotics by the
standard and the higher inoculum tests are detailed in Table 2.
As inoculum effects were consistently detected in CMY-1-like
AmpC b-lactamases-producing isolates, cefotaxime, ceftazidime
Table 1. MICs for ESBL- or AmpC-producing K. pneumoniae isolates according to inoculum
MICa (mg/L) of antibiotics at inocula of 105 and 107 cfu/mL
ESBL-producing K. pneumoniaeb (n = 33)
105
Antibiotics
CTX
CAZ
FEP
IPM
AmpC-producing K. pneumoniaec (n = 28)
107
105
107
range
50%
90%
range
50%
90%
range
50%
90%
range
50%
90%
1 – >256
1 – >256
1 – 128
<
_ 0.25– 4
64
128
8
0.25
256
256
64
0.5
>256
>256
>256
0.5 –8
>256
>256
>256
1
>256
>256
>256
4
8 – >256
16 – >256
<
_ 0.25 – 16
<
_ 0.25 – 1
64
128
1
0.25
>256
>256
4
0.5
>256
>256
16 – >256
0.5– 8
>256
>256
256
4
>256
>256
>256
8
CTX, cefotaxime; CAZ, ceftazidime; FEP, cefepime; IPM, imipenem.
a
50% and 90%, MICs at which 50% and 90% of isolates are inhibited, respectively.
b
TEM, SHV or CTX-M-related b-lactamase-producing K. pneumoniae isolates.
c
DHA-1 or CMY-1-like b-lactamase-producing K. pneumoniae isolates.
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As we previously reported,8 65 K. pneumoniae blood isolates producing ESBLs or AmpC b-lactamases were identified.
b-Lactamases were characterized in 61 of 65 isolates. Twenty-eight
isolates producing AmpC-type enzymes (14 DHA-1 and 14 CMY1-like), 32 isolates producing TEM- or SHV-related ESBLs and
one strain producing a CTX-M-14-like enzyme were included in
this study.8 The ESBL status of the AmpC-producing isolates was
tested by the double-disc diffusion test, using cefepime and
amoxicillin –clavulanic acid discs. After incubation, an enhanced
zone of inhibition between the cefepime disc and clavulanic acid
disc was interpreted as presumptive evidence for the presence of
an ESBL. Two control organisms, E. coli ATCC 25922 and
K. pneumoniae ATCC 700603, were inoculated in each set of tests
for quality control.
Results
AmpC K. pneumoniae and the inoculum effect
Table 2. Standard- and high-inoculum MICs for 28 K. pneumoniae isolates producing AmpC-type b-lactamasesa
MIC (mg/L) of agent at inocula of 105 and 107 cfu/mL
CTX
Isolate no.b
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
7.7
5.4,
5.4,
7.7
7.6,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
5.4,
7.7
7.7
7.7
7.7
7.7
7.7
7.7
7.7, 8.2
7.6, 7.7
7.6, 7.7
7.7, 8.2
7.6, 7.7
7.6, 8.0
7.6, 8.0
7.6, 8.0
7.6, 8.0
7.6, 8.0
8.0
8.0
7.6, 8.0
8.0
8.0
8.0
8.0
7.6, 8.0
8.0
–
FEP
IPM
Type of b-lactamases
105
107
105
107
105
107
105
107
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like
DHA-1, TEM-1-like, SHV-12-like
DHA-1
DHA-1, SHV, TEM-1-like
DHA-1, SHV, TEM-1-like
DHA-1
DHA-1, SHV, SHV-12-like
DHA-1, SHV, TEM-1-like
TEM-1-like, SHV, CMY-1-like
TEM-1-like, SHV, CMY-1-like
TEM-1-like, SHV, CMY-1-like
TEM-1-like, SHV, CMY-1-like
TEM-1-like, SHV, CMY-1-like
CMY-1-like, TEM-1-like
CMY-1-like, TEM-1-like
TEM-1-like, SHV, CMY-1-like
CMY-1-like, TEM-1-like
CMY-1-like, TEM-1-like
CMY-1-like, TEM-1-like
CMY-1-like, TEM-1-like
TEM-1-like, SHV, CMY-1-like
CMY-1-like, TEM-1-like
SHV-18
64
32
64
128
8
32
16
64
64
16
32
32
32
8
64
64
128
64
64
256
256
256
>256
>256
>256
>256
>256
32
8
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
128
32
16
>256
>256
256
32
256
128
128
32
32
64
128
32
64
64
64
64
64
128
64
128
64
32
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
0.5
0.5
<
_ 0.25
16
<
_ 0.25
0.5
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
4
<
_ 0.25
1
2
1
2
1
4
4
4
4
4
4
8
4
1
1
128
256
128
>256
128
>256
64
16
256
128
128
64
>256
128
>256
256
256
256
256
>256
>256
>256
>256
>256
>256
>256
>256
256
128
0.5
0.5
0.5
<
_ 0.25
0.5
1
<
_ 0.25
0.5
0.5
<
_ 0.25
<
_ 0.25
<
_ 0.25
1
0.5
0.5
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
0.5
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
<
_ 0.25
0.5
4
8
4
1
4
8
4
4
8
4
4
4
4
4
4
0.5
1
4
4
8
4
4
4
4
4
4
2
4
4
CTX, cefotaxime; CAZ, ceftazidime; FEP, cefepime; IPM, imipenem.
a
Fourteen DHA-1 and 14 CMY-1-like b-lactamases-producing isolates were included.
b
KP21, 22, 28, 36, 37 and 57 showed a negative ESBL confirmatory test phenotypically.
c
Italics indicate that the b-lactamase with the indicated pI value is inhibited by 0.3 mM cloxacillin and thus represent AmpC enzymes.8
d
ESBL reference strain, K. pneumoniae.
and cefepime were also associated with inoculum effects in all
conjugants of CMY-1-producing isolates.
The increases in cefepime MIC on testing with the higher
inoculum were more prominent in CMY-1-like AmpCproducing isolates than DHA-1 AmpC-producing isolates. In
standard inoculum tests, all isolates were susceptible to imipenem, and cefepime was the next most active agent (96.4%
susceptible). In higher inoculum tests, cefepime was dramatically affected, with susceptibility decreasing from 96.4% in
standard inoculum tests to 0% of isolates inhibited by 8 mg/L
in the higher inoculum tests. Inoculum effects with imipenem
occurred in tests with 85.7% of these isolates (12 of 14 DHA1 isolates and 12 of 14 CMY-1 isolates). Even so, the higher
inoculum MICs of imipenem exceeded 4 mg/L in only four
strains (3 DHA-1 and 1 CMY).
When the ESBL status of the AmpC-producing isolates
was assessed phenotypically, all CMY-1-like AmpC-producing
isolates and eight DHA-1 AmpC-producing isolates showed a
positive ESBL confirmatory test. The remaining six isolates with
a negative ESBL confirmatory test also showed an inoculum
effect with cefepime.
Discussion
In this study of AmpC b-lactamase-producing K. pneumoniae
blood isolates, the inoculum effect was found to be most pronounced in tests with cefepime, cefotaxime and ceftazidime,
with cefepime being at least as affected as cefotaxime and ceftazidime. The inoculum effect was smallest and least common in
tests with imipenem.
An organism may appear susceptible to a drug when tested
in vitro using a standard inoculum but may be ineffective in vivo
due to a high inoculum.4 – 6 A high inoculum effect was recently
reported for cefepime on ESBL-producing and AmpC-producing
isolates of Enterobacteriaceae.3,4 However, no specific AmpC
enzymes were identified,4 and only five (2 ACT-1 and 3 FOX-5)
isolates were included.3 In our study, many relatively new
isolates, harbouring DHA-1 or CMY-1-like b-lactamase, were
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KP9
KP10
KP12
KP18
KP19
KP21
KP22
KP23
KP28
KP36
KP37
KP42
KP43
KP57
KP26
KP29
KP32
KP33
KP34
KP44
KP45
KP48
KP51
KP52
KP53
KP54
KP59
KP61
ATCC 700603d
pI valuec
CAZ
C-I. Kang et al.
by AmpC-type b-lactamase-producing K. pneumoniae to be
prepared to monitor patients closely for signs of treatment
failure.
Acknowledgements
The authors were not supported financially.
References
1. Philippon, A. & Jacoby, G. A. (2002). Plasmid-determined
AmpC-type b-lactamases. Antimicrobial Agents and Chemotherapy 46,
1 –11.
2. Yan, J. J., Ko, W. C., Jung, Y. C. et al. (2002). Emergence of
Klebsiella pneumoniae isolates producing inducible DHA-1 b-lactamase in a university hospital in Taiwan. Journal of Clinical Microbiology
40, 3121– 6.
3. Coudron, P. E., Hanson, N. D. & Climo, M. W. (2003).
Occurrence of extended-spectrum and AmpC b-lactamases in bloodstream isolates of Klebsiella pneumoniae: isolates harbor plasmidmediated FOX-5 and ACT-1 AmpC b-lactamases. Journal of Clinical
Microbiology 41, 772 –7.
4. Thomson, K. S. & Moland, E. S. (2001). Cefepime, piperacillintazobactam, and the inoculum effect in tests with extended-spectrum
b-lactamase-producing Enterobacteriaceae. Antimicrobial Agents and
Chemotherapy 45, 3548–54.
5. Thauvin-Eliopoulos, C., Tripodi, M.-F., Moellering, R. C. et al.
(1997). Efficacies of piperacillin-tazobactam and cefepime in rats with
experimental intra-abdominal abscesses due to an extended-spectrum
b-lactamase-producing strain of Klebsiella pneumoniae. Antimicrobial
Agents and Chemotherapy 41, 1053–7.
6. Paterson, D. L., Ko, W.-C., Gottberg, A. V. et al. (2001).
Outcome of cephalosporin treatment for serious infections due to
apparently susceptible organisms producing extended-spectrum
b-lactamases: implications for the clinical microbiology laboratory.
Journal of Clinical Microbiology 39, 2206–12.
7. Livermore, D. M. (1998). b-Lactamase-mediated resistance and
opportunities for its control. Journal of Antimicrobial Chemotherapy 41,
Suppl. D, 25– 41.
8. Pai, H., Kang, C. I., Byeon, J. H. et al. (2004). Epidemiology
and clinical features of bloodstream infections caused by AmpC type
b-lactamase-producing Klebsiella pneumoniae. Antimicrobial Agents
and Chemotherapy 48, 3720– 8.
9. National Committee for Clinical Laboratory Standards. (2003).
Methods for dilution antimicrobial susceptibility tests for bacteria that
grow aerobically—Sixth Edition: Approved standard M7-A6. NCCLS,
Wayne, PA, USA.
10. Rice, L. B., Yao, J. D. C., Klimm, K. et al. (1991). Efficacy of
different b-lactams against an extended-spectrum b-lactamase-producing Klebsiella pneumoniae strain in the rat intra-abdominal abscess
model. Antimicrobial Agents and Chemotherapy 35, 1243–4.
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tested for inoculum effect. In the molecular epidemiological
study including these isolates, DHA-1 enzyme-producing isolates showed seven types, and CMY-1-like enzyme-producing
isolates revealed two types.8
In general, broad-spectrum cephalosporins are not recommended for the treatment of ESBL-producing organisms.
Initial challenges of the notion that ESBL-producing organisms—for which MICs of broad-spectrum cephalosporins are
in the susceptible range—may not be truly susceptible (when
serious infections are considered) were posed by in vitro
studies of the ‘inoculum effect’ and animal studies. In vitro,
the MICs of cephalosporins increase as the inoculum of
ESBL-producing organisms increases.4,5,10 Experience in experimental animal models of infections with ESBL-producing
organisms has demonstrated ceftriaxone or cefotaxime failure,
despite antibiotic serum levels far exceeding the MIC of the
antibiotic when tested in a conventional inoculum of 105
organisms per mL.10
Studies on determining the therapeutic success or failure of
third-generation cephalosporins in treating infections with
plasmid-mediated inducible AmpC producers, such as our DHA1-producing K. pneumoniae isolates, are lacking. The drugs of
choice for the treatment of infections caused by such organisms
are also undetermined. Based on antimicrobial susceptibility
data, a majority of the AmpC-producing K. pneumoniae isolates
remained susceptible to cefepime and imipenem. Thus, Yan
et al.2 suggested that cefepime and carbapenems could be better
choices for the treatment of infections caused by AmpC producers. However, little information is available about the clinical
effectiveness of cefepime for the treatment of infections caused
by AmpC-type b-lactamase-producing K. pneumoniae.
In our study, the inoculum effect was most consistently
detected for cefepime, cefotaxime and ceftazidime. As previously reported by Livermore,7 it has been proposed that a
major inoculum effect for an antimicrobial agent precludes
its use in serious infections caused by the pathogen, and thus
cefepime may be a less than reliable agent for therapy of
serious infections caused by AmpC b-lactamase-producing
K. pneumoniae. The inoculum effects with cefepime in this
study might have arisen from co-production of ESBLs. However,
cefepime was associated with inoculum effects in six isolates
that showed a negative ESBL confirmatory test. To our knowledge, the clinical implications of the inoculum effect with
respect to cefepime have not been evaluated.4 Therefore, as
Thomson & Moland4 have suggested in their previous report,
until reliable clinical data are available to resolve this issue, it
might be prudent for clinicians who are considering using
cefepime for therapy in cases of serious infections caused
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