Advanced
Distribution of Pseudomonas-Derived Cephalosporinase and Metallo-β-Lactamases in Carbapenem-Resistant Pseudomonas aeruginosa Isolates from Korea
Distribution of Pseudomonas-Derived Cephalosporinase and Metallo-β-Lactamases in Carbapenem-Resistant Pseudomonas aeruginosa Isolates from Korea
Journal of Microbiology and Biotechnology. 2015. Jul, 25(7): 1154-1162
Copyright © 2015, The Korean Society For Microbiology And Biotechnology
  • Received : March 17, 2015
  • Accepted : April 21, 2015
  • Published : July 28, 2015
Download
PDF
e-PUB
PubReader
PPT
Export by style
Article
Author
Metrics
Cited by
TagCloud
About the Authors
Hye Hyun Cho
Department of Biomedical Laboratory Science, Jeonju Kijeon College, Jeonju 560-701, Republic of Korea
Gye Cheol Kwon
Department of Laboratory Medicine, College of Medicine, Chungnam National University, Daejeon 301-721, Republic of Korea
Semi Kim
Department of Laboratory Medicine, College of Medicine, Chungnam National University, Daejeon 301-721, Republic of Korea
Sun Hoe Koo
Department of Laboratory Medicine, College of Medicine, Chungnam National University, Daejeon 301-721, Republic of Korea
shkoo@cnu.ac.kr

Abstract
The emergence of carbapenem resistance among Pseudomonas aeruginosa is an increasing problem in many parts of the world. In particular, metallo-β-lactamases (MBLs) and AmpC βlactamases are responsible for high-level resistance to carbapenem and cephalosporin. We studied the diversity and frequency of β-lactamases and characterized chromosomal AmpC βlactamase from carbapenem-resistant P. aeruginosa isolates. Sixty-one carbapenem-resistant P . aeruginosa isolates were collected from patients in a tertiary hospital in Daejeon, Korea, from January 2011 to June 2014. Minimum inhibitory concentrations (MICs) of four antimicrobial agents were determined using the agar-dilution method. Polymerase chain reaction and sequencing were used to identify the various β-lactamase genes, class 1 integrons, and chromosomally encoded and plasmid-mediated ampC genes. In addition, the epidemiological relationship was investigated by multilocus sequence typing. Among 61 carbapenem-resistant P. aeruginosa isolates, 25 isolates (41.0%) were MBL producers. Additionally, 30 isolates producing PDC ( Pseudomonas -derived cephalosporinase)-2 were highly resistant to ceftazidime (MIC 50 = 256 µg/ml) and cefepime (MIC 50 = 256 µg/ml). Of all the PDC variants, 25 isolates harboring MBL genes showed high levels of cephalosporin and carbapenem resistance, whereas 36 isolates that did not harbor MBL genes revealed relatively low-level resistance (ceftazidime, p < 0.001; cefepime, p < 0.001; imipenem, p = 0.003; meropenem, p < 0.001). The coexistence of MBLs and AmpC β-lactamases suggests that these may be important contributing factors for cephalosporin and carbapenem resistance. Therefore, efficient detection and intervention to control drug resistance are necessary to prevent the emergence of P. aeruginosa possessing this combination of β-lactamases.
Keywords
Introduction
Pseudomonas aeruginosa is a major opportunistic pathogen responsible for hospital-acquired infections and is notorious for its capacity to develop resistance to multiple classes of β-lactams. Recently, carbapenems have been shown to be the most important and effective therapeutic options against serious infections caused by these pathogens, but resistance to these agents is increasingly reported worldwide [1 , 2 , 32] .
Carbapenem resistance in P. aeruginosa is mainly due to a combination of different factors: low outer membrane permeability, overexpression of the efflux pump MexABOprM, hyperproduction of derepressed AmpC chromosomal β-lactamase, and the presence of transferable resistance determinants, in particular, carbapenem-hydrolyzing enzymes [6 , 9 , 19 , 20] . Carbapenem-hydrolyzing enzymes are divided into two types based on molecular classification: serine enzymes, which are derivatives of class A or D enzymes, and metallo enzymes, which belong to class B [25] .
Serine carbapenemases of the Klebsiella pneumoniae carbapenemase (KPC), Guiana extended-spectrum (GES), and oxacilinase (OXA) families have been occasionally reported in this species in certain parts of the world, whereas metallo-β-lactamases (MBLs), particularly Verona imipenemase (VIM), and IMP (active against imipenem) types, are the most widespread and have been reported globally [4 , 12 , 26 , 29] .
In addition to carbapenem-hydrolyzing enzymes, another important mechanism of resistance to β-lactams in P. aeruginosa is the production of chromosomal AmpC β-lactamases, which can be induced or derepressed to confer high-level penicillin and cephalosporin resistance [27] . Inducible AmpC can be upregulated by subinhibitory concentrations of certain β-lactams. Furthermore, mutations can occur in the regulatory components of AmpC, leading to stable hyperproduction of AmpC with concomitant high-level resistance to many classes of β-lactams [21 , 24] . Several chromosomally mediated Pseudomonas -derived cephalosporinases (PDCs) with extended-spectrum cephalosporinase activities have been reported among P. aeruginosa [23] . There are several reports on the prevalence of MBL genes and molecular epidemiology in carbapenemresistant P. aeruginosa isolates from Korea, but the contribution of other mechanisms to carbapenem resistance such as class A and D β-lactamase and PDC genes is unknown.
The aim of this study was to determine the diversity and frequency of β-lactamases and characterize chromosomal AmpC β-lactamase in carbapenem-resistant P. aeruginosa isolates obtained from a tertiary hospital in Korea during a 4-year period. In addition, we investigated the epidemiological relationship and potential correlations between genetic characteristics and resistance to carbapenems.
Materials and Methods
- Bacterial Isolation and Identification
A total of 61 consecutive and non-duplicated carbapenemresistant P. aeruginosa isolates were collected from patients in a tertiary hospital in Daejeon, Korea, from January 2011 to June 2014. The isolates were identified with the Vitek 2 automated ID system (BioMérieux, Hazelwood, MO, USA), and carbapenemresistant P. aeruginosa isolates were selected based on resistance to imipenem and meropenem.
- Antimicrobial Susceptibility Testing
In the antimicrobial susceptibility tests, the minimum inhibitory concentration (MIC) was determined by using the agar dilution method according to the Clinical and Laboratory Standards Institute (CLSI) guidelines [3] . Four antimicrobial agents were tested, including imipenem, meropenem, ceftazidime, and cefepime (Sigma-Aldrich, St. Louis, MO, USA). The interpretation of susceptibility was performed according to the CLSI breakpoints. E. coli ATCC 25922 and P. aeruginosa ATCC 27853 were used as quality control strains.
- Multilocus Sequence Typing
Multilocus sequence typing (MLST) was performed according to the methods described on the P. aeruginosa MLST database website ( http://pubmlst.org/paeruginosa/ ). PCR and sequencing were performed for seven housekeeping genes ( acsA , aroE , guaA , mutL , nuoD , ppsA , and trpE ). The nucleotide sequences of these genes were compared with the sequences submitted to the MLST database to determine the allelic numbers and sequence types (STs).
- Identification and Analysis of β-Lactamase Genes and Integrons
PCR assays were performed to amplify the sequence of MBLs, including the bla IMP , bla VIM , bla GIM , bla SPM , bla SIM , bla NDM , bla AIM , bla DIM , and bla FIM genes, as described previously ( Table 1 ) [17 , 18] . PCR detection of class A and D β-lactamase genes ( bla TEM , bla SHV , bla GES , bla VEB , bla KPC , bla PSE , bla PER , bla CTX-M-1,2,9 group , bla OXA-I,II,III group , bla OXA-23 , bla OXA-24 , bla OXA-48 , bla OXA-51 , and bla OXA-58 ) and class 1, 2, and 3 integrons was also performed as previously described [7 , 11 , 20 , 31] . Sequence analyses were confirmed with the BLAST program at the National Center for Biotechnology Information server ( http://www.ncbi.nlm.nih.gov/ ). The structure of variable regions of integrons was determined by PCR mapping and sequencing.
Oligonucleotides used as primers for amplication and sequencing in this study.
PPT Slide
Lager Image
Oligonucleotides used as primers for amplication and sequencing in this study.
- Genotypic Detection and Sequencing of Chromosomally Encoded and Plasmid-MediatedampCGene
The genotypes of all 61 carbapenem-resistant P. aeruginosa isolates were analyzed for the presence of chromosomal PDC genes and for different families of plasmid-mediated ampC genes by multiplex PCR as described previously [15 , 23] . Amplified PCR products were purified and sequenced; the results of DNA sequencing were compared with known β-lactamase gene sequences using the BLAST program.
- Statistical Analysis
The data were analyzed using SPSS ver. 21.0 (SPSS, Chicago, IL, USA) with one-way analysis of variance. The differences were considered statistically significant at p < 0.05.
Results
- MLST Analysis of Carbapenem-ResistantP. aeruginosa
Among the 61 carbapenem-resistant P. aeruginosa isolates, the sites of isolation were sputum (29 isolates, 47.5%), urine (22 isolates, 36.1%), blood (4 isolates, 6.6%), wounds (3 isolates, 4.9%), bile (2 isolates, 3.3%), and pus (1 isolate, 1.6%) ( Table 2 ). A total of 61 carbapenem-resistant P. aeruginosa isolates were identified as 17 different STs by MLST experiments. ST235 (30 isolates, 49.2%) was the most frequently detected clone. According to frequency, five other detected STs were ST245 (5 isolates, 8.2%), ST654 (5 isolates, 8.2%), ST357 (4 isolates, 6.6%), ST111 (3 isolates, 4.9%), and ST257 (3 isolates, 4.9%). The remaining 11 STs (ST179, ST195, ST244, ST267, ST274, ST589, ST645, ST708, ST1062, ST1455, and ST1663) were each represented by one isolate (1.6%).
MLST analysis of 61 carbapenem-resistantPseudomonas aeruginosaisolates collected during a 4-year period.
PPT Slide
Lager Image
Abbreviations: ST, sequence type.
- Prevalence of β-Lactamases
Of the 61 isolates, 10 isolates (16.4%) harbored OXA-type and 2 (3.3%) harbored Pseudomonas -specific enzyme (PSE)-type enzyme ( Table 3 ). Of the OXA β-lactamases, OXA-10 was the most prevalent, followed by OXA-1 and OXA-2. Fourteen isolates (23.0%) harbored two different β-lactamases, and 12 isolates (19.7%) harbored three enzymes. Of these, MBL genes were identified in 25 isolates (41.0%) harboring bla OXA-1 . Two MBL genes, bla IMP-6 and bla VIM-2 , were identified in 22 (36.1%) and 3 isolates (4.9%), respectively. All 22 isolates carrying the bla IMP-6 gene belonged to ST235 and three isolates carrying the bla VIM-2 gene belonged to ST357.
revalence of Ambler class A, B, and D β-lactamases in 61 carbapenem-resistantPseudomonas aeruginosaisolates.
PPT Slide
Lager Image
revalence of Ambler class A, B, and D β-lactamases in 61 carbapenem-resistant Pseudomonas aeruginosa isolates.
- Structure of Class 1 Integrons
Class 1 integrons were detected in 36 (59.0%) of the 61 carbapenem-resistant P. aeruginosa isolates and no class 2 or 3 integrons were found. The gene cassettes found in this study were divided into six types (Type A, B, C, D, E, and F) according to the cassette composition ( Table 4 ). Type A (4.0 kb), obtained in 18 isolates, carried the aadB - cmlA - bla OXA-10 - aadA1 gene cassette. Eleven isolates of type B (5.5 kb) belonged to ST235 and carried bla IMP-6 - qac - aacA4 - bla OXA-10-   aadA2 . Type C (1.8 kb), found in two isolates, carried aacA4 - bla OXA-2 - orfD , and type D (1.2 kb) had aadA6 - orfD (2 isolates). Two isolates contained type E (1.0 kb) carrying the aadA4 gene cassette. Type F (2.5 kb) was detected in only one isolate and carried aadA4 - bla OXA-10-   aadA2 .
Schematic representation of gene cassette structures located in the class 1 integron isolated from 61 carbapenem-resistantPseudomonas aeruginosaisolates.
PPT Slide
Lager Image
Schematic representation of gene cassette structures located in the class 1 integron isolated from 61 carbapenem-resistant Pseudomonas aeruginosa isolates.
- Identification of AmpC Variants
On performing PCR for the presence of chromosomal ampC gene, all 61 isolates of P. aeruginosa harbored PDC gene while the plasmid-mediated ampC gene was not present. Sequencing analysis of the PCR product of the chromosomal ampC gene revealed that 61 isolates obtained six variants (PDC-1, PDC-2, PDC-3, PDC-5, PDC-7, and PDC-8) ( Table 5 ).
Distribution of AmpC-type variants (PDC) and MIC of β-lactam drugs for 61 carbapenem-resistantPseudomonas aeruginosaisolates.
PPT Slide
Lager Image
Abbreviations: N, number of isolates; CAZ, ceftazidime; CFP, cefepime; IPM, imipenem; MEM, meropenem.
The most frequent variant was PDC-2 (30 isolates, 49.2%) and PDC-3 was the second most frequently detected variant (10 isolates, 16.4%). Thirty isolates producing PDC-2 were highly resistant to ceftazidime (MIC 50 = 256 µg/ml) and cefepime (MIC 50 = 256 µg/ml). Meanwhile, the remaining 31 isolates showed full or intermediate susceptibility, with the ceftazidime MIC 50 ranging from 8 to 16 µg/ml. Additionally, 25 isolates harboring MBL genes were highly resistant to ceftazidime (MIC range 64 to >256 µg/ml), cefepime (MIC range 64 to >256 µg/ml), imipenem (MIC range >256 µg/ml), and meropenem (MIC range >256 µg/ml) ( Table 6 ). In contrast, 36 isolates that did not contain MBL genes showed relatively low resistance, with MICs ranging from 2 to 128 µg/ml for ceftazidime, 2 to >256 µg/ml for cefepime, 8 to >256 µg/ml for imipenem, and 8 to >256 µg/ml for meropenem.
AmpC-type variants (PDC) and β-lactam MIC according to expression of the MBL gene in 61 carbapenem-resistantPseudomonas aeruginosaisolates.
PPT Slide
Lager Image
Abbreviations: N, number of isolates; CAZ, ceftazidime; CFP, cefepime; IPM, imipenem; MEM, meropenem
Discussion
Resistance to β-lactams (particularly carbapenem and cephalosporin) in P. aeruginosa has been increasingly reported worldwide, and this is also the case in Korea. According to previous Korean National Surveillance Antimicrobial Resistance (KONSAR) studies, from 2005 to 2011, resistance rates of P. aeruginosa to imipenem increased from 19% to 26%, and to ceftazidime increased from 19% to 23% [33] . This study analyzed various genes of P. aeruginosa isolates that are responsible for resistance to carbapenems. Class D OXA β-lactamases were more frequently detected than class A in P. aeruginosa (16.4% versus 3.3%). In particular, OXA-10 was only observed in ST235 isolates (19 isolates), and was accompanied by bla IMP-6 in 12 isolates (63.2%). Similarly, a previous study found that 35 (60.3%) of 58 OXA-10-producing isolates harbored bla IMP-6 and/or bla VIM-2 , and belonged to only ST235 [1] . In addition, 25 (41.0%) carbapenem-resistant P. aeruginosa isolates were MBL producers.
Compared with a previous study, the rates of MBL production showed a 2.5-fold increase from 16.2% in 2008– 2012 to 41.0% in 2011–2014 among carbapenem-resistant P. aeruginosa isolates [2] . Among the 22 ST235 IMP-6-producing isolates, 11 isolates (50.0%) shared an identical class 1 integron with a gene cassette array ( bla IMP-6 - qac - aacA4 - bla OXA-1 - aadA1 ) between the 5’ and 3’ conserved sequence. The bla VIM-2 gene was identified in three isolates of ST357.
Mechanisms of drug resistance in AmpC β-lactamase can either be chromosomally or plasmid-mediated. The majority of AmpC β-lactamases are chromosomally mediated and are found in Serratia , Pseudomonas , Acinetobacter , Citrobacter , and Enterbacter spp. Chromosomally mediated resistance is due to mutation(s) in the bacterial DNA, and such genes are not easily transferable to other bacterial species [5 , 8] . In the present study, six variants of the chromosomally mediated ampC enzyme PDC were identified in all 61 carbapenem-resistant P. aeruginosa isolates. The most frequent AmpC-type variant was PDC-2, containing the substitutions G27D, A97V, T105A, and V205L. Substitutions in this region have been previously linked to the broadening of the enzyme’s hydrolytic spectrum, facilitating the degradation of compounds such as ceftazidime [10 , 22] . In our study, 30 isolates harboring PDC-2 exhibited high levels of resistance to ceftazidime (MIC 50 = 256 µg/ml) and cefepime (MIC 50 = 256 µg/ml). Additionally, of the 30 isolates, 20 (66.7%) belonged to ST235 and most of the ST235 isolates were recovered from urine (14 isolates, 70%). Another study from France reported 10 variants of a PDC (PDC 1-10) gene, in which several variants showed reduced susceptibility to ceftazidime, cefepime, and imipenem [23 , 28] .
Plasmid-mediated AmpC β-lactamases can spread laterally, making them transferable to other bacteria. Therefore, they are frequently seen in many bacterial species such as E. coli , K. pneumonia , Salmonella spp., Citrobacter freundii , Enterobacter aerogenes , and Proteus mirabilis [5 , 16] . In this study, we were unable to detect plasmid-mediated ampC genes, which is consistent with a previous study by Wang et al. [30] , who reported that no plasmid-mediated ampC genes were detected among 258 carbapenem-resistant P. aeruginosa isolates.
Of all the PDC variants, 25 isolates harboring MBL genes showed high levels of cephalosporin (MIC range for ceftazidime and cefepime, 64 to >256 µg/ml) and carbapenem (MIC range for imipenem and meropenem, >256 µg/ml) resistance, whereas 36 isolates that did not harbor MBL genes revealed relatively low-level resistance (MIC range for ceftazidime, 2–128 µg/ml; cefepime, 2 to >256 µg/ml; imipenem and meropenem, 8 to >256 µg/ml). These results highlight the importance of MBL genes in cephalosporin and carbapenem resistance in P. aeruginosa (ceftazidime, cefepime, and meropenem, p < 0.001; imipenem, p = 0.003).
Similarly, Bae et al. [1] reported that production of IMP-6 and VIM-2 MBLs is the main mechanism for acquiring resistance to ceftazidime and carbapenems in P. aeruginosa isolates. In addition, Neyestanaki et al. [11] found that the production of MBLs and AmpC β-lactamases was the major emerging mechanism of resistance to carbapenem among P. aeruginosa isolates in Teharan, Iran. Similarly, combinations of various β-lactamases have recently been reported in studies from India, Brazil, Italy, and Argentina [13 , 14] .
In conclusion, the coexistence of MBLs and AmpC β-lactamases suggests that these may be important contributing factors for cephalosporin and carbapenem resistance. Therefore, efficient detection and intervention to control drug resistance are necessary to prevent the emergence of P. aeruginosa possessing this combination of β-lactamases.
References
Bae IK , Suh B , Jeong SH , Wang KK , Kim YR , Yong D 2014 Molecular epidemiology ofPseudomonas aeruginosaclinical isolates from Korea producing β-lactamases with extended-spectrum activity. Diagn. Microbiol. Infect. Dis. 79 373 - 377    DOI : 10.1016/j.diagmicrobio.2014.03.007
Cho HH , Kwon KC , Sung JY , Koo SH 2013 Prevalence and genetic analysis of multidrug-resistantPseudomonas aeruginosaST235 isolated from a hospital in Korea, 2008-2012. Ann. Clin. Lab. Sci. 43 414 - 419
Clinical and Laboratory Standards Institute 2012 Performance standards for antimicrobial susceptibility testing: twentysecond informational supplement. M100-S22. CLSI Wayne, Pennsylavania
Cornaglia G , Giamarellou H , Rossolini GM 2011 Metallo-β-lactamases: a last frontier for β-lactams? Lancet Infect. Dis. 11 381 - 393    DOI : 10.1016/S1473-3099(11)70056-1
Grover N , Sahni AK , Bhattacharya S 2013 Therapeutic challenges of ESBLS and AmpC β-lactamase producers in a tertiary care center. Med. J. Armed Forces India 69 4 - 10    DOI : 10.1016/j.mjafi.2012.02.001
Huang YT , Chang SC , Lauderdale TL , Yang AJ , Wang JT 2007 Molecular epidemiology of carbapenem-resistantPseudomonas aeruginosacarrying metallo-beta-lactamase genes in Taiwan. Diagn. Microbiol. Infect. Dis. 59 211 - 216    DOI : 10.1016/j.diagmicrobio.2007.01.009
Hu LF , Chang X , Ye Y , Wang ZX , Shao YB , Shi W 2011 Stenotrophomonas maltophiliaresistance to trimethoprim/ sulfamethoxazole mediated by acquisition ofsulanddfrAgenes in a plasmid-mediated class 1 integron. Int. J. Antimicrob. Agents 37 230 - 234    DOI : 10.1016/j.ijantimicag.2010.10.025
Jacoby GA 2009 AmpC β-lactamases. Clin. Microbiol. Rev. 22 161 - 182    DOI : 10.1128/CMR.00036-08
Lister PD , Wolter DJ , Hanson ND 2009 AntibacterialresistantPseudomonas aeruginosa: clinical impact and complex regulation of chromosomally encoded resistance mechanisms. Clin. Microbiol. Rev. 22 582 - 610    DOI : 10.1128/CMR.00040-09
Mammeri H , Nordmann P 2007 Extended-spectrum cephalosporinases in Enterobacteriaceae. Anti-Infect. Agents Med. 6 71 - 82    DOI : 10.2174/187152107779314133
Neyestanaki DK , Mirsalehian A , Rezagholizadeh F , Jabalameli F , Taherikalani M , Emaneini M 2014 Determination of extended spectrum β-lactamases, metallo-β-lactamases and AmpC-β-lactamases among carbapenem resistantPseudomonas aeruginosaisolated from burn patients. Burns 40 1556 - 1561    DOI : 10.1016/j.burns.2014.02.010
Pasteran F , Faccone D , Gomez S , De Bunder S , Spinelli F , Rapoport M 2012 Detection of an international multiresistant clone belonging to sequence type 654 involved in the dissemination of KPC-producingPseudomonas aeruginosain Argentina. J. Antimicrob. Chemother. 67 1291 - 1293    DOI : 10.1093/jac/dks032
Pasteran F , Faccone D , Petroni A , Rapoport M , Galas M , Vázquez M 2005 Novel variant (bla(VIM-11)) of the metallo-{β}-lactamase bla(VIM) family in a GES-1 extendedspectrum-{β}-lactamase-producingPseudomonas aeruginosaclinical isolate in Argentina. Antimicrob. Agents Chemother. 49 474 - 475    DOI : 10.1128/AAC.49.1.474-475.2005
Pellegrino FL , Teixeira LM , Carvalho Md Mda G , Aranha Nouér S , Pinto De Oliveira M , Mello Sampaio JL 2002 Occurrence of a multidrug-resistantPseudomonas aeruginosaclone in different hospitals in Rio de Janeiro, Brazil. J. Clin. Microbiol. 40 2420 - 2424    DOI : 10.1128/JCM.40.7.2420-2424.2002
Pérez-Pérez FJ , Hanson ND 2002 Detection of plasmidmediated AmpC beta-lactamase genes in clinical isolates by using multiplex PCR. J. Clin. Microbiol. 40 2153 - 2162    DOI : 10.1128/JCM.40.6.2153-2162.2002
Philippon A , Arlet G , Jacoby GA 2002 Plasmid-determined AmpC-type beta-lactamases. Antimicrob. Agents Chemother. 46 1 - 11    DOI : 10.1128/AAC.46.1.1-11.2002
Poirel L , Walsh TR , Cuvillier V , Nordmann P 2011 Multiplex PCR for detection of acquired carbapenemase genes. Diagn. Microbiol. Infect. Dis. 70 119 - 123    DOI : 10.1016/j.diagmicrobio.2010.12.002
Pollini S , Maradei S , Pecile P , Olivo G , Luzzaro F , Docquier JD 2013 FIM-1, a new acquired metallo-β-lactamase from aPseudomonas aeruginosaclinical isolate from Italy. Antimicrob. Agents Chemother. 57 410 - 416    DOI : 10.1128/AAC.01953-12
Poole K 2011 Pseudomonas aeruginosa: resistance to the max. Front Microbiol. 2 65 -    DOI : 10.3389/fmicb.2011.00065
Qing Y , Cao KY , Fang ZL , Huang YM , Zhang XF , Tian GB 2014 Outbreak of PER-1 and diversity of β-lactamases among ceftazidime-resistantPseudomonas aeruginosaclinical isolates. J. Med. Microbiol. 63 386 - 392    DOI : 10.1099/jmm.0.069427-0
Quale J , Bratu S , Gupta J , Landman D 2006 Interplay of efflux system,ampC, andoprDexpression in carbapenem resistance ofPseudomonas aeruginosaclinical isolates. Antimicrob. Agents Chemother. 50 1633 - 1641    DOI : 10.1128/AAC.50.5.1633-1641.2006
Raimondi A , Sisto F , Nikaido H 2001 Mutation inSerratia marcescensAmpC β-lactamase producing high-level resistance to ceftazidime and cefpirome. Antimicrob. Agents Chemother. 45 2331 - 2339    DOI : 10.1128/AAC.45.8.2331-2339.2001
Rodríguez-Martínez JM , Poirel L , Nordmann P 2009 Extended-spectrum cephalosporinases inPseudomonas aeruginosa. Antimicrob. Agents Chemother. 53 1766 - 1771    DOI : 10.1128/AAC.01410-08
Rodríguez-Martínez JM , Poirel L , Nordmann P 2009 Molecular epidemiology and mechanisms of carbapenem resistance inPseudomonas aeruginosa. Antimicrob. Agents Chemother. 53 4783 - 4788    DOI : 10.1128/AAC.00574-09
Sanbongi Y , Shimizu A , Suzuki T , Nagaso H , Ida T , Maebashi K 2009 Classification of OprD sequence and correlation with antimicrobial activity of carbapenem agents inPseudomonas aeruginosaclinical isolates collected in Japan. Microbiol. Immunol. 53 361 - 367    DOI : 10.1111/j.1348-0421.2009.00137.x
Sevillano E , Gallego L , García-Lobo JM 2009 First detection of the OXA-40 carbapenemase inP. aeruginosaisolates, located on a plasmid also found inA. baumannii. Pathol. Biol. (Paris) 57 493 - 495    DOI : 10.1016/j.patbio.2008.05.002
Tian GB , Adams-Haduch JM , Bogdanovich T , Wang HN , Doi Y 2011 PME-1, an extended-spectrum β-lactamase identified inPseudomonas aeruginosa. Antimicrob. Agents Chemother. 55 2710 - 2713    DOI : 10.1128/AAC.01660-10
Upadhyay S , Mishra S , Sen MR , Banerjee T , Bhattacharjee A 2013 Co-existence ofPseudomonas-derived cephalosporinase among plasmid encoded CMY-2 harbouring isolates ofPseudomonas aeruginosain north India. Indian J. Med. Microbiol. 31 257 - 260    DOI : 10.4103/0255-0857.115629
Viedma E , Juan C , Acosta J , Zamorano L , Otero JR , Sanz F 2009 Nosocomial spread of colistin-only-sensitive sequence type 235Pseudomonas aeruginosaisolates producing the extended-spectrum β-lactamases GES-1 and GES-5 in Spain. Antimicrob. Agents Chemother. 53 4930 - 4933    DOI : 10.1128/AAC.00900-09
Wang J , Zhou JY , Qu TT , Shen P , Wei ZQ , Yu YS 2010 Molecular epidemiology and mechanisms of carbapenem resistance inPseudomonas aeruginosaisolates from Chinese hospitals. Int. J. Antimicrob. Agents 35 486 - 491    DOI : 10.1016/j.ijantimicag.2009.12.014
Woodford N , Ellington MJ , Coelho JM , Turton JF , Ward ME , Brown S 2006 Multiplex PCR for genes encoding prevalent OXA carbapenemases inAcinetobacterspp. Int. J. Antimicrob. Agents 27 351 - 353    DOI : 10.1016/j.ijantimicag.2006.01.004
Wright LL , Turton JF , Livermore DM , Hopkins KL , Woodford N 2015 Dominance of international ‘high-risk clones’ among metallo-β-lactamase-producingPseudomonas aeruginosain the UK. J. Antimicrob. Chemother. 70 103 - 110    DOI : 10.1093/jac/dku339
Yong D , Shin HB , Kim YK , Cho J , Lee WG , Ha GY 2014 Increase in the prevalence of carbapenem-resistantAcinetobacterisolates and ampicillin-resistant non-typhoidalSalmonellaspecies in Korea: a KONSAR study conducted in 2011. Infect. Chemother. 46 84 - 93    DOI : 10.3947/ic.2014.46.2.84