AAC Accepted Manuscript Posted Online 26 May 2015 Antimicrob. Agents Chemother. doi:10.1128/AAC.00830-15 Copyright © 2015, American Society for Microbiology. All Rights Reserved.
1
Activity of imipenem with relebactam against Gram negative pathogens from New York City
2 3
Amabel Lapuebla,a Marie Abdallaha, Olawole Olafisoyea, Christopher Cortesb, Carl Urbanb,
4
David Landmana, John Qualea#
5 6
Division of Infectious Diseases, SUNY Downstate Medical Center, Brooklyn, NY, USAa; The
7
Dr. James J. Rahal Jr. Division of Infectious Diseases, New York Hospital Queens, Flushing,
8
NY, USAb
9 10
Corresponding author: John Quale Email: [email protected]
11
Running title: Imipenem with relebactam for Gram negative bacilli
12 13 14 15 16 17 18 19 20 21 22 23
1
24
ABSTRACT
25
Imipenem with relebactam was active against E. coli, K. pneumoniae, and Enterobacter spp,
26
including KPC-producing isolates. Loss of OmpK36 in KPC-producing K. pneumoniae affected
27
the susceptibility of this combination. Enhanced activity was evident against P. aeruginosa,
28
including those with depressed oprD and increased ampC expression. However, the addition of
29
relebactam to imipenem did not provide added benefit against A. baumannii. The combination
30
of imipenem with relebactam demonstrated activity against KPC-producing Enterobacteriaceae
31
and multidrug-resistant P. aeruginosa.
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
2
47
The spread of carbapenemases in Enterobacteriaceae, Pseudomonas aeruginosa, and
48
Acinetobacter baumannii has created therapeutic dilemmas for clinicians. In particular, the
49
acquisition of metallo-β-lactamases and the class A enzyme KPC affords protection against
50
virtually all β-lactam therapeutic agents (1). The worldwide dissemination of bacteria possessing
51
blaKPC has been especially striking (2). First reported in the Northeast United States in the 1990s,
52
pathogens harboring this β-lactamase are now endemic in countries in Asia, South America, and
53
Europe (2).
54
Novel β-lactamase inhibitors are being developed to restore the utility of β-lactam antibiotics
55
against carbapenemase-producing pathogens (3,4). Avibactam and relebactam are
56
diazabicyclooctane inhibitors with activity against a wide spectrum of β-lactamases, including
57
class A (ESBLs, KPC) and class C (AmpC) enzymes (3,4). In this report, we determined the
58
activity of imipenem with relebactam against Gram negative pathogens from medical centers in
59
New York City.
60
From November 2013 – January 2014, single patient isolates of E coli, K. pneumoniae,
61
Enterobacter spp., P. aeruginosa, and A. baumannii were collected from eleven hospitals in
62
Brooklyn and Queens, NY. Susceptibility tests were performed in a central research laboratory
63
using the agar dilution method, and interpreted as per CLSI guidelines (5). Isolates of E. coli and
64
K. pneumoniae were presumed to harbor ESBLs if they were nonsusceptible to ceftazidime
65
and/or ceftriaxone and did not have blaKPC. Imipenem was tested both with and without the
66
presence of relebactam (fixed concentration of 4µg/ml). For the purpose of this study, imipenem
67
breakpoints were used to interpret susceptibility to imipenem plus relebactam. Cephalosporin-
68
resistant isolates were tested by PCR for the presence of blaKPC, blaOXA-23-type and blaOXA-24-type ,
69
blaVIM, blaIMP, and blaNDM using previously described primers (6-9). Isolates of K. pneumoniae
3
70
with blaKPC and A. baumannii with blaOXA23-type underwent genetic fingerprinting by the rep-PCR
71
method with ERIC-2 primer, as previously described (6).
72
Susceptibility testing of imipenem with and without relebactam was also performed on a
73
collection of previously characterized isolates of K. pneumoniae, P. aeruginosa, and A.
74
baumannii (10-13). Expression of genes encoding β-lactamases, efflux pumps, and porins were
75
correlated with MICs of imipenem with relebactam.
76
Surveillance study results
77
A total of 2778 isolates of E. coli were gathered during the three month surveillance study.
78
Susceptibilities are given in the table. Of the blaKPC negative isolates, 383 were considered to
79
have ESBLs and all were susceptible to imipenem. The imipenem MIC50/MIC90 values for the
80
ESBL isolates were 0.25/0.5 µg/ml; with the addition of relebactam, the corresponding values
81
were 0.25/0.25 µg/ml. Five isolates harbored blaKPC. For these 5 isolates, the imipenem MICs
82
ranged from 0.5 - >32 µg/ml. With the addition of relebactam, the MICs fell to 0.12-0.5 µg/ml.
83
A total of 891 isolates of K. pneumoniae were collected (Table). Of the blaKPC negative
84
isolates, 185 were considered ESBL producers. All of the ESBL producers were susceptible to
85
imipenem, with MIC50/MIC90 values of 0.25/0.5 µg/ml. With the addition of relebactam, the
86
imipenem MIC50/MIC90 values were 0.25/0.5 µg/ml. For 111 isolates that harbored blaKPC, the
87
imipenem MIC50/MIC90 values were 16/>16 µg/ml. With the addition of relebactam, the
88
MIC50/MIC90 values fell to 0.25/1 µg/ml; three isolates had MICs of 2 µg/ml (intermediate to
89
imipenem). Twenty-three isolates with blaKPC, from 11 different hospitals, underwent
90
fingerprinting. Eight rep-PCR types were identified, including 12 isolates that belonged to one
91
clone (data not shown).
4
92
There were 211 Enterobacter spp. isolates (Table), including 90 E. aerogenes and 120 E.
93
cloacae. Three isolates of E. aerogenes and four isolates of E. cloacae harbored blaKPC. For these
94
seven isolates, six were nonsusceptible to imipenem, and the MICs ranged from 0.5 to >16
95
µg/ml. With the addition of relebactam, the MICs ranged from 0.12 to 2 µg/ml, with six
96
susceptible to imipenem.
97
Among 490 isolates of P. aeruginosa, the imipenem MIC50/MIC90 values were 2/16 µg/ml
98
(Table). These values fell to 0.5/2 µg/ml with the addition of relebactam. Among the 144 isolates
99
nonsusceptbile to imipenem, the addition of relebactam resulted in MIC50/MIC90 values of 1/2
100 101
µg/ml. Imipenem MICs with and without relebactam were similar among 158 isolates of A.
102
baumannii (Table). Fifty-eight were found to have blaOXA-23-like, two carried blaOXA-24-like, and
103
one harbored blaKPC. Eighteen isolates, from eight hospitals, with blaOXA-23-like underwent
104
fingerprinting. A total of 10 rep-PCR types were identified, including six belonging to a single
105
clone (data not shown). For the isolates harboring blaOXA-23-like, the imipenem MIC50/MIC90
106
values were >16/>16 µg/ml with or without the addition of relebactam. Similarly, the imipenem
107
MICs did not change with the addition of relebactam for the two isolates with blaOXA-24-like. For a
108
single isolate with blaKPC, the imipenem MIC fell from >16 to 4 µg/ml with the addition of
109
relebactam.
110
Results with previously characterized isolates.
111
Fourteen previously characterized isolates of KPC-producing K. pneumoniae were examined.
112
(10,11). In the presence of relebactam, imipenem MICs did not correlate with the expression of
113
ramA, acrB, or blaKPC. Similarly, there was no correlation among 8 isolates without frameshift
114
mutations in ompK35. Ten isolates had expression of ompK36 greater than the control; imipenem
5
115
MICs ranged from 2->16 µg/ml. With the addition of relebactam, all of the imipenem MICs were
116
0.25-0.5 µg/ml. Four isolates had reduced expression of ompK36; the imipenem MICs for these
117
isolates were 4, >16, >16, and >16 µg/ml. With the addition of relebactam, the imipenem MICs
118
fell to 0.5, 2, 2, and 8 µg/ml. The last isolate did not have an amplifiable ompK36.
119
Thirty previously characterized isolates of P. aeruginosa were analyzed (12); none possessed
120
carbapenemases. Six isolates were wild-type regarding ampC and oprD expression (similar to
121
control). Imipenem MICs ranged from 2-4 µg/ml for this group; all had imipenem MICs of 1
122
µg/ml with the addition of relebactam. Fourteen isolates had reduced oprD expression with wild-
123
type ampC expression. For these isolates, the imipenem MICs ranged from 1 to >16 µg/ml. With
124
the addition of relebactam, the MICs fell to 0.25-8 µg/ml (average 1.8 ± 1.9 µg/ml). Ten isolates
125
had reduced oprD expression and upregulated ampC expression. The imipenem MICs for these
126
isolates ranged from 2->16 µg/ml; when combined with relebactam the MICs ranged from 1-8
127
µg/ml (average 4.6 ± 2.9 µg/ml).
128
Twenty-eight isolates of previously characterized A. baumannii isolates were also included
129
(13). In general, imipenem MICs were unchanged with the addition of relebactam. There was no
130
clear relationship between expression of ampC, blaoxa-51, adeB, and abeM and MICs to imipenem
131
with relebactam.
132
The global spread of carbapenemases, in pathogens already resistant to other classes of
133
antibiotics, has posed a serious therapeutic challenge for clinicians. RPX7009, avibactam, and
134
relebactam are novel β-lactamase inhibitors with activity against primarily class A and class C β-
135
lactamses (3,4). When combined with imipenem, relebactam has demonstrated a dose-dependent
136
synergy against a small number of Enterobacteriaceae harboring blaKPC (14,15). In this report, at
137
a fixed concentration of 4 µg/ml, relebactam restored imipenem susceptibility to 97% of K.
6
138
pneumoniae with blaKPC. When a group of well-characterized isolates were tested, down-
139
regulation of ompK36 appeared to partially offset the protective effect of relebactam. Restoration
140
of imipenem susceptibility was also found in a small number of blaKPC-containing isolates of E.
141
coli and Enterobacter spp.
142
In addition, relebactam with imipenem has demonstrated activity against P. aeruginosa,
143
including isolates with depressed oprD and increased ampC expression (14,15). In our study, the
144
addition of relebactam resulted in an approximately fourfold decrease in the imipenem
145
MIC50/MIC90, and imipenem susceptibility rates increased from 70% to 98% when relebactam
146
was added. Restoration of imipenem activity was noted with isolates with depressed oprD
147
expression with and without increased ampC expression, although the MICs did continue to run
148
higher than in the wild type isolates.
149
However, the addition of relebactam did not improve the activity of imipenem against A.
150
baumannii. MICs were unchanged in isolates with overexpression of ampC and/or blaOXA-51,
151
suggesting lack of relebactam activity against these enzymes. Diminished inhibitor activity has
152
been observed in K. pneumoniae with OXA-48, and absent activity against pathogens harboring
153
metallo-β-lactamases (15). Further development of new antimicrobial agents directed against
154
pathogens harboring these β-lactamases is sorely needed.
155 156 157
ACKNOWLEDGMENT This work was supported in part by a research grant from Merck &
158
Co., Inc.
159 160
7
161
REFERENCES
162
1. Patel G, Bonomo RA. 2013. “Stormy waters ahead”: global emergence of carbapenemases.
163
Frontiers Microbiol 4:1-17.
164
2. Nordmann P, Cuzon G, Nass T. 2009. The real threat of Klebsiella pneumoniae
165
carbapenemase-producing bacteria. Lancet Infect Dis 9:228-236.
166
3. Drawz SM, Papp-Wallace KM, Bonomo RA. 2014. New β-lactamase inhibitors: a
167
therapeutic renaissance in an MDR world. Antimicrob Agents Chemother 58:1835-1846.
168
4. Toussaint KA, Gallagher JC. 2015. β-lactam/β-lactamase inhibitor combinations: From then
169
to now. Ann Pharmacother 49:86-98.
170
5. Clinical and Laboratory Standards Institute. 2014. Performance Standards for
171
Antimicrobial Susceptibility Testing. Approved standard M100-S24. Twenty-fourth
172
Informational Supplement. Clinical Laboratory Standards Institute, Wayne, PA.
173
6. Landman D, Babu E, Shah N. Kelly P, Olawole O, Backer M, Bratu S, Quale J. 2012.
174
Transmission of carbapenem-resistant pathogens in New York City hospitals: progress and
175
frustration. J Antimicrob Chemother 67:1427-1431.
176
7. Woodford N, Ellington MJ, Coelho JM, Turton JF, Ward E, Brown S, Amyes SGB,
177
Livermore DM. 2006. Multiplex PCR for genes encoding prevalent OXA carbapenemases in
178
Acinetobacter spp. Int. J. Antimicrob. Agents 27:351-353.
179
8. Nordmann P, Poirel L. 2002. Emerging carbapenemases in Gram-negative aerobes. Clin.
180
Microbiol. Infect. 8:321-31.
181
9. Doumith M, Warner M, Weinben M, Livermore DM, Woodford N. Dissemination of a
182
novel metallo-beta-lactamase, NDM-1, in diverse Enterobacteriaceae in the UK. Abstr 49th
183
Intersci Conf on Antimicrob Agents Chemother, abstr C1-058.
8
184
10. Landman D, Bratu S, Quale J. 2009. Contribution of OmpK36 to carbapenem
185
susceptibility in KPC-producing Klebsiella pneumoniae. J Med Microbiol 58:1303-1308.
186
11. Bratu S, Landman D, George A, Salvani J, Quale J. 2009. Correlation of the expression of
187
acrB and the regulatory genes marA, soxS, and ramA with antimicrobial resistance in clinical
188
isolates of Klebsiella pneumoniae endemic to New York City. J Antimicrob Chemother 64:278-
189
283.
190
12. Quale J, Bratu S, Gupta J, Landman D. 2006. Interplay of efflux system, ampC and oprD
191
expression in carbapenem resistance of Pseudomonas aeruginosa clinical isolates. Antimicrob
192
Agents Chemother 50:1633-1641.
193
13. Bratu S, Landman D, Martin DA Georgescu C, Quale J. 2008. Correlation of
194
antimicrobial resistance with β-lactamases, the OmpA-like porin, and efflux pumps in clinical
195
isolates of Acinetobacter baumannii endemic to New York City. Antimicrob. Agents Chemother.
196
52:2999-3005.
197
14. Hirsh EB, Ledesma KR, Chang K-T, Schwartz MS, Motyl MR, Tam VH. 2012. In vitro
198
activity of MK-7655, a novel β-lactamase inhibitor, in combination with imipenem against
199
carbapenem-resistant Gram-negative bacteria. Antimicrob Agents Chemother 56:3753-3757.
200
15. Livermore DM, Warner M, Mushtaq S. 2013. Activity of MK-7655 combined with
201
imipenem against Enterobacteriaceae and Pseudomonas aeruginosa. J Antimicrob Chemother
202
68:2286-2290.
203 204 205
9
206
TABLE Susceptibility results for Enterobacteriaceae, P. aeruginosa, and A. baumannii collected
207
during the surveillance study. MIC50
MIC90
Range
Percent susceptible
µg/ml E. coli (n=2778) Ertapenem
0.008
0.03
≤ 0.002 - >32
99.6%
Imipenem
0.25
0.25
≤ 0.03 - >32
99.9%
0.25/4
0.25/4
≤ 0.03/4 – 1/4
100%
Ertapenem
≤ 0.125
8
≤ 0.125 - >8
86%
Imipenem
0.25
4
0.06 - >16
88%
0.25/4
0.25/4
0.06/4 – 2/4
99.3%
Imipenem + relebactam K. pneumoniae (n=891)
Imipenem + relebactam
blaKPC-possessing K. pneumoniae (n=111) Ertapenem
>8
>8
0.5 - >8
2%
Imipenem
16
>16
0.5 - >16
9%
0.25/4
1/4
0.12/4 – 2/4
97%
Ertapenem
≤ 0.125
0.25
≤ 0.125 - >8
93%
Imipenem
0.5
1
≤ 0.03 - >16
90%
0.25/4
0.5/4
≤ 0.03/4 – 2/4
99%
2
16
≤ 0.03 - >16
70%
0.5/4
2/4
≤ 0.03/4 - >16/4
98%
Imipenem + relebactam Enterobacter sp. (n=211)
Imipenem + relebactam P. aeruginosa (n=490) Imipenem Imipenem + relebactam
10
Imipenem-resistant P. aeruginosa (n=144) Imipenem Imipenem-relebactam
8
>16
4->16
0%
1/4
2/4
0.25/4->16/4
92%
4
>16
≤ 0.03 - >16
49%
2/4
>16/4
≤ 0.03/4 - >16/4
51%
>16
>16
≤ 0.03 - >16
12%
>16/4
>16/4
≤ 0.03/4 - >16/4
12%
A. baumannii (n=158) Imipenem Imipenem + relebactam
blaOXA-23-possessing A. baumannii (n=58) Imipenem Imipenem + relebactam 208
11
1
Activity of imipenem with relebactam against Gram negative pathogens from New York City
2 3
Amabel Lapuebla,a Marie Abdallaha, Olawole Olafisoyea, Christopher Cortesb, Carl Urbanb,
4
David Landmana, John Qualea#
5 6
Division of Infectious Diseases, SUNY Downstate Medical Center, Brooklyn, NY, USAa; The
7
Dr. James J. Rahal Jr. Division of Infectious Diseases, New York Hospital Queens, Flushing,
8
NY, USAb
9 10
Corresponding author: John Quale Email: [email protected]
11
Running title: Imipenem with relebactam for Gram negative bacilli
12 13 14 15 16 17 18 19 20 21 22 23
1
24
ABSTRACT
25
Imipenem with relebactam was active against E. coli, K. pneumoniae, and Enterobacter spp,
26
including KPC-producing isolates. Loss of OmpK36 in KPC-producing K. pneumoniae affected
27
the susceptibility of this combination. Enhanced activity was evident against P. aeruginosa,
28
including those with depressed oprD and increased ampC expression. However, the addition of
29
relebactam to imipenem did not provide added benefit against A. baumannii. The combination
30
of imipenem with relebactam demonstrated activity against KPC-producing Enterobacteriaceae
31
and multidrug-resistant P. aeruginosa.
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
2
47
The spread of carbapenemases in Enterobacteriaceae, Pseudomonas aeruginosa, and
48
Acinetobacter baumannii has created therapeutic dilemmas for clinicians. In particular, the
49
acquisition of metallo-β-lactamases and the class A enzyme KPC affords protection against
50
virtually all β-lactam therapeutic agents (1). The worldwide dissemination of bacteria possessing
51
blaKPC has been especially striking (2). First reported in the Northeast United States in the 1990s,
52
pathogens harboring this β-lactamase are now endemic in countries in Asia, South America, and
53
Europe (2).
54
Novel β-lactamase inhibitors are being developed to restore the utility of β-lactam antibiotics
55
against carbapenemase-producing pathogens (3,4). Avibactam and relebactam are
56
diazabicyclooctane inhibitors with activity against a wide spectrum of β-lactamases, including
57
class A (ESBLs, KPC) and class C (AmpC) enzymes (3,4). In this report, we determined the
58
activity of imipenem with relebactam against Gram negative pathogens from medical centers in
59
New York City.
60
From November 2013 – January 2014, single patient isolates of E coli, K. pneumoniae,
61
Enterobacter spp., P. aeruginosa, and A. baumannii were collected from eleven hospitals in
62
Brooklyn and Queens, NY. Susceptibility tests were performed in a central research laboratory
63
using the agar dilution method, and interpreted as per CLSI guidelines (5). Isolates of E. coli and
64
K. pneumoniae were presumed to harbor ESBLs if they were nonsusceptible to ceftazidime
65
and/or ceftriaxone and did not have blaKPC. Imipenem was tested both with and without the
66
presence of relebactam (fixed concentration of 4µg/ml). For the purpose of this study, imipenem
67
breakpoints were used to interpret susceptibility to imipenem plus relebactam. Cephalosporin-
68
resistant isolates were tested by PCR for the presence of blaKPC, blaOXA-23-type and blaOXA-24-type ,
69
blaVIM, blaIMP, and blaNDM using previously described primers (6-9). Isolates of K. pneumoniae
3
70
with blaKPC and A. baumannii with blaOXA23-type underwent genetic fingerprinting by the rep-PCR
71
method with ERIC-2 primer, as previously described (6).
72
Susceptibility testing of imipenem with and without relebactam was also performed on a
73
collection of previously characterized isolates of K. pneumoniae, P. aeruginosa, and A.
74
baumannii (10-13). Expression of genes encoding β-lactamases, efflux pumps, and porins were
75
correlated with MICs of imipenem with relebactam.
76
Surveillance study results
77
A total of 2778 isolates of E. coli were gathered during the three month surveillance study.
78
Susceptibilities are given in the table. Of the blaKPC negative isolates, 383 were considered to
79
have ESBLs and all were susceptible to imipenem. The imipenem MIC50/MIC90 values for the
80
ESBL isolates were 0.25/0.5 µg/ml; with the addition of relebactam, the corresponding values
81
were 0.25/0.25 µg/ml. Five isolates harbored blaKPC. For these 5 isolates, the imipenem MICs
82
ranged from 0.5 - >32 µg/ml. With the addition of relebactam, the MICs fell to 0.12-0.5 µg/ml.
83
A total of 891 isolates of K. pneumoniae were collected (Table). Of the blaKPC negative
84
isolates, 185 were considered ESBL producers. All of the ESBL producers were susceptible to
85
imipenem, with MIC50/MIC90 values of 0.25/0.5 µg/ml. With the addition of relebactam, the
86
imipenem MIC50/MIC90 values were 0.25/0.5 µg/ml. For 111 isolates that harbored blaKPC, the
87
imipenem MIC50/MIC90 values were 16/>16 µg/ml. With the addition of relebactam, the
88
MIC50/MIC90 values fell to 0.25/1 µg/ml; three isolates had MICs of 2 µg/ml (intermediate to
89
imipenem). Twenty-three isolates with blaKPC, from 11 different hospitals, underwent
90
fingerprinting. Eight rep-PCR types were identified, including 12 isolates that belonged to one
91
clone (data not shown).
4
92
There were 211 Enterobacter spp. isolates (Table), including 90 E. aerogenes and 120 E.
93
cloacae. Three isolates of E. aerogenes and four isolates of E. cloacae harbored blaKPC. For these
94
seven isolates, six were nonsusceptible to imipenem, and the MICs ranged from 0.5 to >16
95
µg/ml. With the addition of relebactam, the MICs ranged from 0.12 to 2 µg/ml, with six
96
susceptible to imipenem.
97
Among 490 isolates of P. aeruginosa, the imipenem MIC50/MIC90 values were 2/16 µg/ml
98
(Table). These values fell to 0.5/2 µg/ml with the addition of relebactam. Among the 144 isolates
99
nonsusceptbile to imipenem, the addition of relebactam resulted in MIC50/MIC90 values of 1/2
100 101
µg/ml. Imipenem MICs with and without relebactam were similar among 158 isolates of A.
102
baumannii (Table). Fifty-eight were found to have blaOXA-23-like, two carried blaOXA-24-like, and
103
one harbored blaKPC. Eighteen isolates, from eight hospitals, with blaOXA-23-like underwent
104
fingerprinting. A total of 10 rep-PCR types were identified, including six belonging to a single
105
clone (data not shown). For the isolates harboring blaOXA-23-like, the imipenem MIC50/MIC90
106
values were >16/>16 µg/ml with or without the addition of relebactam. Similarly, the imipenem
107
MICs did not change with the addition of relebactam for the two isolates with blaOXA-24-like. For a
108
single isolate with blaKPC, the imipenem MIC fell from >16 to 4 µg/ml with the addition of
109
relebactam.
110
Results with previously characterized isolates.
111
Fourteen previously characterized isolates of KPC-producing K. pneumoniae were examined.
112
(10,11). In the presence of relebactam, imipenem MICs did not correlate with the expression of
113
ramA, acrB, or blaKPC. Similarly, there was no correlation among 8 isolates without frameshift
114
mutations in ompK35. Ten isolates had expression of ompK36 greater than the control; imipenem
5
115
MICs ranged from 2->16 µg/ml. With the addition of relebactam, all of the imipenem MICs were
116
0.25-0.5 µg/ml. Four isolates had reduced expression of ompK36; the imipenem MICs for these
117
isolates were 4, >16, >16, and >16 µg/ml. With the addition of relebactam, the imipenem MICs
118
fell to 0.5, 2, 2, and 8 µg/ml. The last isolate did not have an amplifiable ompK36.
119
Thirty previously characterized isolates of P. aeruginosa were analyzed (12); none possessed
120
carbapenemases. Six isolates were wild-type regarding ampC and oprD expression (similar to
121
control). Imipenem MICs ranged from 2-4 µg/ml for this group; all had imipenem MICs of 1
122
µg/ml with the addition of relebactam. Fourteen isolates had reduced oprD expression with wild-
123
type ampC expression. For these isolates, the imipenem MICs ranged from 1 to >16 µg/ml. With
124
the addition of relebactam, the MICs fell to 0.25-8 µg/ml (average 1.8 ± 1.9 µg/ml). Ten isolates
125
had reduced oprD expression and upregulated ampC expression. The imipenem MICs for these
126
isolates ranged from 2->16 µg/ml; when combined with relebactam the MICs ranged from 1-8
127
µg/ml (average 4.6 ± 2.9 µg/ml).
128
Twenty-eight isolates of previously characterized A. baumannii isolates were also included
129
(13). In general, imipenem MICs were unchanged with the addition of relebactam. There was no
130
clear relationship between expression of ampC, blaoxa-51, adeB, and abeM and MICs to imipenem
131
with relebactam.
132
The global spread of carbapenemases, in pathogens already resistant to other classes of
133
antibiotics, has posed a serious therapeutic challenge for clinicians. RPX7009, avibactam, and
134
relebactam are novel β-lactamase inhibitors with activity against primarily class A and class C β-
135
lactamses (3,4). When combined with imipenem, relebactam has demonstrated a dose-dependent
136
synergy against a small number of Enterobacteriaceae harboring blaKPC (14,15). In this report, at
137
a fixed concentration of 4 µg/ml, relebactam restored imipenem susceptibility to 97% of K.
6
138
pneumoniae with blaKPC. When a group of well-characterized isolates were tested, down-
139
regulation of ompK36 appeared to partially offset the protective effect of relebactam. Restoration
140
of imipenem susceptibility was also found in a small number of blaKPC-containing isolates of E.
141
coli and Enterobacter spp.
142
In addition, relebactam with imipenem has demonstrated activity against P. aeruginosa,
143
including isolates with depressed oprD and increased ampC expression (14,15). In our study, the
144
addition of relebactam resulted in an approximately fourfold decrease in the imipenem
145
MIC50/MIC90, and imipenem susceptibility rates increased from 70% to 98% when relebactam
146
was added. Restoration of imipenem activity was noted with isolates with depressed oprD
147
expression with and without increased ampC expression, although the MICs did continue to run
148
higher than in the wild type isolates.
149
However, the addition of relebactam did not improve the activity of imipenem against A.
150
baumannii. MICs were unchanged in isolates with overexpression of ampC and/or blaOXA-51,
151
suggesting lack of relebactam activity against these enzymes. Diminished inhibitor activity has
152
been observed in K. pneumoniae with OXA-48, and absent activity against pathogens harboring
153
metallo-β-lactamases (15). Further development of new antimicrobial agents directed against
154
pathogens harboring these β-lactamases is sorely needed.
155 156 157
ACKNOWLEDGMENT This work was supported in part by a research grant from Merck &
158
Co., Inc.
159 160
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206
TABLE Susceptibility results for Enterobacteriaceae, P. aeruginosa, and A. baumannii collected
207
during the surveillance study. MIC50
MIC90
Range
Percent susceptible
µg/ml E. coli (n=2778) Ertapenem
0.008
0.03
≤ 0.002 - >32
99.6%
Imipenem
0.25
0.25
≤ 0.03 - >32
99.9%
0.25/4
0.25/4
≤ 0.03/4 – 1/4
100%
Ertapenem
≤ 0.125
8
≤ 0.125 - >8
86%
Imipenem
0.25
4
0.06 - >16
88%
0.25/4
0.25/4
0.06/4 – 2/4
99.3%
Imipenem + relebactam K. pneumoniae (n=891)
Imipenem + relebactam
blaKPC-possessing K. pneumoniae (n=111) Ertapenem
>8
>8
0.5 - >8
2%
Imipenem
16
>16
0.5 - >16
9%
0.25/4
1/4
0.12/4 – 2/4
97%
Ertapenem
≤ 0.125
0.25
≤ 0.125 - >8
93%
Imipenem
0.5
1
≤ 0.03 - >16
90%
0.25/4
0.5/4
≤ 0.03/4 – 2/4
99%
2
16
≤ 0.03 - >16
70%
0.5/4
2/4
≤ 0.03/4 - >16/4
98%
Imipenem + relebactam Enterobacter sp. (n=211)
Imipenem + relebactam P. aeruginosa (n=490) Imipenem Imipenem + relebactam
10
Imipenem-resistant P. aeruginosa (n=144) Imipenem Imipenem-relebactam
8
>16
4->16
0%
1/4
2/4
0.25/4->16/4
92%
4
>16
≤ 0.03 - >16
49%
2/4
>16/4
≤ 0.03/4 - >16/4
51%
>16
>16
≤ 0.03 - >16
12%
>16/4
>16/4
≤ 0.03/4 - >16/4
12%
A. baumannii (n=158) Imipenem Imipenem + relebactam
blaOXA-23-possessing A. baumannii (n=58) Imipenem Imipenem + relebactam 208
11
