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. 2002 Sep;46(9):3031–3034. doi: 10.1128/AAC.46.9.3031-3034.2002

Prospective Survey of β-Lactamases Produced by Ceftazidime- Resistant Pseudomonas aeruginosa Isolated in a French Hospital in 2000

Christophe De Champs 1,*, Laurent Poirel 2, Richard Bonnet 1, Danielle Sirot 1, Catherine Chanal 1, Jacques Sirot 1, Patrice Nordmann 2
PMCID: PMC127436  PMID: 12183264

Abstract

In 2000, at the Université d'Auvergne teaching hospital in Clermont-Ferrand, France, 44 (6.2%) strains of Pseudomonas aeruginosa were found to be resistant to ceftazidime. After genotyping, 34 strains were selected. Nine had an additional β-lactamase: OXA-21 (n = 6), PSE-1 (CARB-2) (n = 2), or PER-1 (n = 1). Ceftazidime resistance was related solely to the overproduction of the cephalosporinase in 30 strains. Sequencing of five blaAmpC genes encoding cephalosporinases with different pIs showed 99% identity with the ampC gene of P. aeruginosa PAO1.


Resistance to extended-spectrum cephalosporins in Pseudomonas aeruginosa is associated in most cases with the overproduction of a naturally produced cephalosporinase (19). Derepression of this AmpC β-lactamase affects all β-lactams to various extents, which may lead to the misdetection of other acquired β-lactamases. Enzymes hydrolyzing extended-spectrum cephalosporins of Ambler classes A, B, and D have been reported in P. aeruginosa (19). Among the extended-spectrum β-lactamases (ESBLs) of class A, TEM-4 (22), TEM-24 (15), TEM-42 (16), PER-1 (18), SHV-2a (19), VEB-1 (21), and GES-2 (26) have been encountered.

Class B enzymes, IMP-1 (33), VIM-1 (10), VIM-2 (23), and VIM-related enzymes (11), hydrolyze carbapenems in addition to extended-spectrum cephalosporins.

The extended-spectrum class D enzymes are OXA-2 derivatives (OXA-15 [4] and OXA-32 [24]), OXA-10 derivatives (OXA-11 [7], OXA-14 [3], OXA-16 [5], OXA-17 [6], OXA-19 [17], and OXA-28 [25]), and OXA-18 (20).

Other mechanisms implicated in resistance to β-lactams in P. aeruginosa are impermeability of the outer membrane and increased efflux (12) The aim of this study was to characterize the β-lactamases produced by ceftazidime-resistant P. aeruginosa isolates.

Of the 713 nonduplicate P. aeruginosa strains isolated from the Université d'Auvergne teaching hospital in Clermont-Ferrand, France, between 1 January and 30 September 2000, 44 (6.2%) were resistant to ceftazidime, as determined by the disk diffusion method on Mueller-Hinton agar according to the recommendations of the Antibiogram Committee of the French Society for Microbiology (zone diameter, <15 mm; www.sfm.asso.fr/Sect4/atbuk.html). This prevalence of ceftazidime resistance was higher than the 4% prevalence in 1996 reported in a previous French national multicenter study (2). Isolates were identified with the ID 32 GN system (BioMérieux, Marcy l'Etoile, France). A duplicate isolate was defined as an isolate with the same antibiotic resistance phenotype as another isolate from the same patient during the same course of infection. The 44 strains were typed by random amplification of polymorphic DNA (RAPD) with two primers, ERIC-2 and 208, as described previously (Table 1) (14, 30). Isoelectric focusing analysis was performed with 6% polyacrylamide gels containing ampholines (Amersham Pharmacia Biotech, Uppsala, Sweden) with a pH range of 3.5 to 10, as reported previously (19). Among the 44 strains, 34 were selected on the basis of antibiotic resistance patterns, pIs, and patterns by RAPD analysis (Table 2). The chromosomal cephalosporinases focused at five pIs: 8.4 (n = 13), 8.0 (n = 8), 8.0 and 8.4 (n = 7), 7.8 (n = 4), and 8.6 (n = 2). Three additional β-lactamases were found at pIs 7.0 (n = 6), 5.7 (n = 2), and 5.4 (n = 1). The strains were distributed into 33 different RAPD profiles.

TABLE 1.

Oligonucleotides used as primers for amplification and/or sequencing

Primer Sequence Positiona Strand Reference
ERIC-2 5′-AAGTAAGTGACTGGGGTGAGC-3′ NAb NA 30
208 5′-ACGGCCGACC-3′ NA NA 14
PER-A 5′-TGACGATCTGGAACCTTT-3′ 1053 Forward This study
PER-B 5′-AACTGCATAACCTACTCC-3′ 204 Reverse This study
OC1 5′-AATGGCAATCAGCGCTTC-3′ 311 Forward 1
OC3 5′-GCGCGACTGTGATGTATA-3′ 1009 Reverse 1
AMPC-PAC 5′-GGGGCGGTTTCTCATGCAGCCAACG-3′ 510 Forward This study
AMPC-PAD 5′-GAAGCGCTCATGGCACCATCATAGCC-3′ 1822 Reverse This study
AMPC-PAG 5′-CGACCTTGTAGTAACCGC-3′ 1421 Reverse This study
AMPC-28 5′-TCCTCATGCGCGATAC-3′ 549 Forward This study
AMPC-PAB1 5′-GTTGGAATAGAGGC-3′ 1090 Reverse This study
OXA-2,3 5′-GCCAAAGGCACGATAGTTGT-3′ 239 Forward This study
OXB-2,3 5′-GCGTCCGAGTTGACTGCCGG-3′ 939 Reverse This study
a

Numbers correspond to the position of the first 5′ base of each oligonucleotide according to the numbering of the nucleotide sequences with GenBank accession nos. Z21957 (blaPER-1), M69058 (blaPSE-1), X03037 (blaOXA-2), and X54719 (blaAmpC).

b

NA, not applicable.

TABLE 2.

Characteristics of the 34 ceftazidime-resistant P. aeruginosa isolates

Strainj pl Cephalosporinase inhibition with CLO ata:
MIC (μl/ml)b
Sp actc (mU/mg) [mean ± SD]) βlad Typee Type by RAPD analysis Site of recovery
250 μg/ml 500 μg/ml TIC TCC PIP TZP CAZ FEP ATM IPM MEM
1 7.8 + + 128 128 128 128 128 32 64 64 8 730 ± 89 NAg 1 Rectal swab
2 7.8 + + 64 64 64 64 32 16 16 16 8 NDh 1 2 Wound
3 7.8 + 256 256 128 128 64 32 64 1 0.5 0.611 ± 20 6 3 Urines
4 7.8 + 5.4 256 64 16 16 128 32 128 16 16 PER-1 11 4 Rectal swab
5 8.0 + 256 256 256 256 64 32 64 1 0.5 15,373 ± 940 NA 5 Rectal swab
6 8.0 + + 64 64 32 16 32 8 16 1 0.25 1,566 ± 22 6 6 BPf
7 8.0 + 128 128 128 128 32 32 16 16 16 1,602 ± 93 11 7 Wound
8 8.0 + + 128 128 128 128 64 32 32 2 0.5 321 ± 1 3 8 Urine
9 8.0 + + 64 64 64 32 32 16 16 32 8 231 ± 8 11 9 Urine
101 8.0 + 128 128 128 128 64 16 32 1 0.5 1,679 ± 327 6 10 Rectal swab
11 8.0 + + 128 128 128 128 128 32 128 16 8 124 ± 21 NA 11 Rectal swab
12 8.0 + + 256 256 256 256 64 64 64 0.5 1 ND 11 12 Rectal swab
13 8.4 + 512 512 256 256 128 64 128 2 4 1,010 ± 24 NA 13 Blood
14 8.4 + 128 128 128 128 64 32 32 16 8 1,243 ± 52 6 14 BP
15 8.4 + 256 256 256 256 128 64 128 8 4 10,054 ± 30 6 15 BP
16 8.4 + + 128 128 128 128 64 32 32 4 2 688 ± 28 1 16 BP
17 8.4 + + 128 128 128 128 64 16 16 2 0.5 373 ± 12 NA 17 BP
18 8.4 + 5.7 + 2,048 1,024 256 256 64 32 32 32 16 PSE-1 12 18 Rectal swab
19 8.4 + 5.7 + 2,048 256 256 128 32 16 16 32 4 PSE-1 12 19 BP
20 8.4 + 7.0 + 256 256 64 32 64 32 16 2 0.25 OXA-21 3 20 PDFk
21 8.4 + 7.0 + 128 128 64 64 32 16 16 32 8 OXA-21 4 21 BP
22 8.4 + 7.0 + 256 256 64 64 32 32 32 32 8 OXA-21 3 22 BP
23 8.4 + 7.0 + 256 256 64 64 64 32 16 2 0.25 OXA-21 4 23 Urine
24 8.4 + 7.0 + 256 256 128 128 64 32 32 2 0.5 OXA-21 6 24 Rectal swab
25 8.4 + 7.0 + 256 256 64 64 64 32 16 2 0.25 OXA-21 3 25 Blood
26 8.0 + 8.4 + + 128 128 128 128 64 32 32 16 8 894 ± 66 11 26 BP
27 8.0 + 8.4 + + 128 128 128 128 64 32 32 0.5 1 680 ± 80 11 27 BP
28 8.0 + 8.4 + + 128 128 64 64 32 16 16 16 8 693 ± 29 11 28 BP
29 8.0 + 8.4 + 256 256 128 128 64 32 32 1 0.5 678 ± 9 6 22 BP
30 8.0 + 8.4 + + 128 128 64 64 128 32 128 16 8 177 ± 21 NA 29 Rectal swab
31 8.0 + 8.4 + + 64 64 64 64 32 8 32 32 8 641 ± 10 11 30 Wound
32 8.0 + 8.4 + + 64 64 64 32 32 8 16 2 0.12 1,761 ± 50 1 31 Rectal swab
33 8.6 + + 128 128 64 32 64 16 64 1 0.25 52 ± 1 6 32 Rectal swab
34 8.6 + 256 256 128 128 64 64 64 0.5 0.5 ND 3 33 BP
PAO1 8.0 NAPi NAP ≤16 ≤16 ≤4 ≤4 ≤2 2 4 1 0.25 <0.001 1
a

Cephalosporinase inhibition test on Mueller-Hinton agar with cloxacillin (CLO) at 250 or 500 μg/ml. +, ceftazidime zone diameter increase of >10 mm; −, ceftazidime zone diameter increase of ≤10 mm.

b

Abbreviations: TIC, ticarcillin; TCC, ticarcillin-clavulanate (2 μg/ml); PIP, piperacillin; TZP, piperacillin-tazobactam (4 μg/ml); CAZ, ceftazidime; FEP, cefepime; ATM, aztreonam; IPM, imipenem; MEM, meropenem.

c

AmpC activity was not determined for strains producing an additional β-lactamase.

d

βla, additional β-lactamase.

e

O serotype.

f

BP, bronchopulmonary sample.

g

NA, no agglutination.

h

ND, not done.

i

NAP, not applicable.

j

The pairs of strains 10 and 24, 12 and 14, and 22 and 29 were each isolated from the same patient.

k

PDF, peritoneal dialysis fluid.

The MICs of drugs alone or in combination with a fixed concentration of clavulanate (2 μg/ml) and tazobactam (4 μg/ml) were determined by the dilution method in Mueller-Hinton agar with an inoculum of 104 CFU per spot, as described previously (20) (Table 2). The MICs of ceftazidime were in a narrow range from 32 to 128 μg/ml. The MICs of ticarcillin ranged from 64 to 2,048 μg/ml. The use of clavulanate did not restore susceptibility to ticarcillin. The MICs of piperacillin were between 16 and 256 μg/ml, and the MICs of aztreonam were between 16 and 128 μg/ml. The strains were moderately resistant to cefepime (MICs, 8 to 64 μg/ml). Fifteen strains were resistant to imipenem (MICs, >8 μg/ml), and of these, three were resistant to meropenem (MICs, >8 μg/ml).

Cephalosporinase inhibition, evaluated by the disk diffusion method on Mueller-Hinton agar containing cloxacillin at 250 or 500 μg/ml, was considered significant when the ceftazidime zone diameter increased by >10 mm. P. aeruginosa PAO1 was used as the reference strain (8). For 25 strains which did not have pI values that might correspond to those for an additional β-lactamase, ceftazidime activity was partially restored by cloxacillin at 250 μg/ml (n = 15) or only by cloxacillin at 500 μg/ml (n = 10). For these 25 strains without an additional β-lactamase, the level of production of the AmpC enzymes was measured by determination of their specific β-lactamase activities. Cultures were grown overnight at 37°C in 3 liters of brain heart infusion (Biokar Diagnostics, Beauvais, France). Bacterial suspensions were disrupted by sonication and centrifuged as described previously (19). The supernatants were dialyzed against 3 liters of 100 mM NaCl overnight at 4°C. Then, the specific β-lactamase activities of the crude extracts were determined by a computerized microacidimetric method described elsewhere (9) with 225 mM benzylpenicillin as the substrate. The total protein concentration in the enzyme preparation was estimated by a protein assay (Bio-Rad, Richmond, Calif.) with bovine serum albumin (Sigma Chemical Co., St. Louis, Mo.) as the standard. One unit of specific β-lactamase activity was defined as the amount of enzyme which hydrolyzes 1 μmol of benzylpenicillin per min and per mg of protein at 37°C and at pH 7. For 21 strains the specific activity was 100- to 1,000-fold greater than that of PAO1, with values ranging from 124 to 15,373 mU mg−1 (Table 2). Variations in levels of resistance to ceftazidime were weakly related to different levels of enzyme overproduction (i.e., an MIC of 64 μg/ml corresponds to specific activities of 52 mU mg−1 for strain 33 and 15,373 mU mg−1 for strain 5).

The ampC genes of the strains that produced five cephalosporinases with different pI values were amplified with primers AMPC-PAC and AMPC-PAD (Table 1) under the following conditions: 94°C for 5 min and then 30 cycles of 94°C for 1 min, 50°C for 3 min, and 72°C for 3 min, with a single final extension at 72°C for 15 min. The PCR products were sequenced with the primers AMPC-PAD, AMPC-PAG, AMPC-28, and AMPC-PAB1 (Table 1). Sequence analysis showed a low level of sequence diversity (0.17 to 0.75%) and 99% nucleotide identity with the ampC gene of P. aeruginosa strain PAO1 (GenBank accession no. X54719). Compared to the PAO1 ampC gene sequence (8), all ampC genes encoding enzymes with pIs different from 8.0 harbored the mutation A866→G, which led to the substitution Thr105→Ala (Table 3).

TABLE 3.

Substitution in blaAmpC genes according to the pI value for each cephalosporinase and comparison with the sequence of the blaAmpC gene of P. aeruginosa strain PAO1 (pI 8.0)

Nucleotide (amino acid) positiona in PAO1 Nucleotide (amino acid) substitution in cephalosporinase with accession no. (pI) of:
AY083593 (7.8) AY083595 (8.0) AY083592 (8.4) AF490770 (8.0 + 8.4) AY083594 (8.6)
G789 (Arg79) A (Gln)
A866 (Thr105) G (Ala) G (Ala) G (Ala) G (Ala)
C883 (Arg110) T
A916 (Ala121) G
C994 (Phe147) T
C1060 (Tyr169) T
T1080 (Leu176) G (Arg)
G1150 (Arg199) A
G1166 (Val205) T (Leu) C (Leu)
C1204 (Asp217) T
T1243 (Tyr230) C C C C C
C1399 (Thr282) T
G1519 (Pro322) A A
T1585 (Gly344) C C C
C1639 (Gly362) A A
G1725 (Gly391) C
a

Numbering is according to that for the blaAmpC gene and that for the deduced amino acid sequence of P. aeruginosa PAO1 with GenBank accession no. X54719.

Genes encoding enzymes of pI 8.0 + 8.4 and pI 8.4 harbored a mutation at position 1166 that led to the substitution Val205→Leu. The ampC gene encoding the enzyme of pI 7.8 harbored the mutation G789→A, which led to the substitution Arg79→Gln, and that encoding the enzyme of pI 8.6 harbored the mutation T1080→G, which led to the substitution Leu176→Arg. The Arg79→Gln substitution is associated with a change in charges and may have been responsible for the decrease in the pI value from 8.0 to 7.8, as reported previously (28). However, enzymes with identical pIs do not necessarily share identical amino acid sequences, and the different pIs suggested that some bands correspond to cleaved derivatives (isoenzymes) of the cephalosporinase, as reported previously (32).

For eight of the nine strains with an additional β-lactamase, ceftazidime activity was restored only by cloxacillin at 500 μg/ml (strains 18 to 25), and so ceftazidime resistance was very likely due to hydrolysis by the derepressed chromosomal cephalosporinase. For strain 4 the activity of ceftazidime was not restored by cloxacillin at 500 μg/ml. Strain 4 was the only one which had a positive modified disk synergy test result with ceftazidime and clavulanate (27). The genes of the six β-lactamases with a pI of 7.0 were amplified with OXA-2 primers (primers OXA-2,3 and OXB-2,3). Nucleotide sequence analysis of the blaOXA PCR products revealed a blaOXA-21 sequence with only one silent mutation (T697→C) in the genes of four isolates compared to the sequence of blaOXA-21 previously reported for Acinetobacter baumannii (31) (EMBL database accession no. Y10693). The six strains that produced OXA-21 had different RAPD patterns (data not shown). To our knowledge, this is the first report of OXA-21 in P. aeruginosa.

The blaPSE-1 gene was detected in two strains by PCR with primers OC1 and OC3 (Table 1), and a protein with a pI of 5.7 conferred a very high level of resistance to ticarcillin (MICs, >2,048 μg/ml) and ticarcillin-clavulanate (MICs, 256/1,024 μg/ml).

The blaPER-1 gene of the strain producing the β-lactamase with a pI of 5.4 was identified by PCR with primers PER-A and PER-B (Table 1) and sequencing. Epidemics caused by strains with this enzyme, previously reported in Turkey (29) and Italy (13), are now observed in France.

The carbapenem resistance observed in 15 strains was not related to enzymatic hydrolysis by a carbapenem-hydrolyzing β-lactamase. Although several ESBLs were reported in P. aeruginosa, their prevalences were very low in our study.

Acknowledgments

We thank Rolande Perroux, Marlène Jan, and Dominique Rubio for technical assistance. We are also grateful to J. Watts for reading the English manuscript.

This work was supported in part by a grant from the Ministère de l'Education Nationale, de la Recherche et de la Technologie.

REFERENCES

  • 1.Arlet, G., and A. Philippon. 1991. Construction by polymerase chain reaction and intragenic DNA probes for three main types of transferable β-lactamases (TEM, SHV, CARB). FEMS Microbiol. Lett. 82:19-26. [DOI] [PubMed] [Google Scholar]
  • 2.Cavallo, J. D., R. Fabre, F. Leblanc, M. H. Nicolas-Chanoine, A. Thabaut, and the GERPB. 2000. Antibiotic susceptibility and mechanisms of β-lactam resistance in 1310 strains of Pseudomonas aeruginosa: a French multicentre study (1996). J. Antimicrob. Chemother. 46:133-136. [DOI] [PubMed] [Google Scholar]
  • 3.Danel, F., L. M. C. Hall, D. Gur, and D. M. Livermore. 1995. OXA-14, another extended-spectrum variant of OXA-10 (PSE-2) β-lactamase from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 39:1881-1884. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Danel, F., M. Lucinda, C. Hall, D. Gur, and D. M. Livermore. 1997. OXA-15, an extended-spectrum variant of OXA-2 β-lactamase isolated from a Pseudomonas aeruginosa strain. Antimicrob. Agents Chemother. 41:785-790. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Danel, F., L. M. Hall, D. Gur, and D. M. Livermore. 1998. OXA-16, a further extended-spectrum variant of OXA-10 β-lactamase, from two Pseudomonas aeruginosa isolates. Antimicrob. Agents Chemother. 42:3117-3122. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Danel, F., L. M. Hall, B. Duke, D. Gur, and D. M. Livermore. 1999. OXA-17, a further extended-spectrum variant of OXA-10 β-lactamase, isolated from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 43:1362-1366. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Hall, L. M. C., D. M. Livermore, D. Gur, M. Akova, and H. E. Akalin. 1993. OXA-11, an extended-spectrum variant of OXA-10 (PSE-2) β-lactamase from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 37:1637-1644. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Kiewitz, C., and B. Tümmler. 2000. Sequence diversity of Pseudomonas aeruginosa: impact on population structure and genome evolution. J. Bacteriol. 182:3125-3135. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Labia, R., J. Andrillon, and F. Le Goffic. 1973. Computerized microacidimetric determination of β-lactamase Michaelis-Menten constants. FEBS Lett. 33:42-44. [DOI] [PubMed] [Google Scholar]
  • 10.Lauretti, L., M. L. Riccio, A. Mazzariol, G. Cornaglia, G. Amicosante, R. Fontana, and G. M. Rossolini. 1999. Cloning and characterization of blaVIM, a new integron-borne metallo-β-lactamase gene from a Pseudomonas aeruginosa clinical isolate. Antimicrob. Agents Chemother. 43:1584-1590. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Livermore, D. M., and N. Woodford. 2000. Carbapenemases: a problem in waiting? Curr. Opin. Microbiol. 3:489-495.D. M. [DOI] [PubMed] [Google Scholar]
  • 12.Livermore, D. M. 2001. Of Pseudomonas, porins pumps and carbapenems. J. Antimicrob. Chemother. 47:247-250. [DOI] [PubMed] [Google Scholar]
  • 13.Luzzaro, F., E. Mantengoli, M. Perilli, G. Lombardi, V. Orlandi, A. Orsatti, G. Amicosante, G. M. Rossolini, and A. Toniolo. 2001. Dynamics of a nosocomial outbreak of multidrug-resistant Pseudomonas aeruginosa producing the PER-1 extended-spectrum β-lactamase. J. Clin. Microbiol. 39:1865-1870. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Mahenthiralingam, E., M. E. Campbell, J. Foster, J. S. Lam, and D. P. Speert. 1996. Random amplified polymorphic DNA typing of Pseudomonas aeruginosa isolates recovered from patients with cystic fibrosis. J. Clin. Microbiol. 34:1129-1135. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Marchandin, H., H. Jean-Pierre, C. De Champs, D. Sirot, H. Darbas, P. F. Perigault, and C. Carriere. 2000. Production of a TEM-24 plasmid-mediated extended-spectrum β-lactamase by a clinical isolate of Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 44:213-216. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Mugnier, P., P. Dubrous, I. Casin, G. Arlet, and E. Collatz. 1996. A TEM-derived extended-spectrum beta-lactamase in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 40:2488-2493. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Mugnier, P., I. Casin, A. T. Bouthors, and E. Collatz. 1998. Novel OXA-10-derived extended-spectrum β-lactamases selected in vivo or in vitro. Antimicrob. Agents Chemother. 42:3113-3116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Nordmann, P., E. Ronco, T. Naas, C. Duport, Y. Michel-Briand, and R. Labia. 1993. Characterization of a novel extended-spectrum β-lactamase from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 37:962-969. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Nordmann, P., and M. Guibert. 1998. Extended-spectrum β-lactamases in Pseudomonas aeruginosa. J. Antimicrob. Chemother. 42:128-131. [DOI] [PubMed] [Google Scholar]
  • 20.Philippon, L. N., T. Naas, A. T. Bouthors, V. Barakett, and P. Nordmann. 1997. OXA-18, a class D clavulanic acid-inhibited extended-spectrum β-lactamase from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 41:2188-2195. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Poirel, L., T. Naas, M. Guibert, E. B. Chaibi, R. Labia, and P. Nordmann. 1999. Molecular and biochemical characterization of VEB-1, a novel class A extended-spectrum beta-lactamase encoded by an Escherichia coli integron gene. Antimicrob. Agents Chemother. 43:573-581. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Poirel, L., E. Ronco, T. Naas, and P. Nordmann. 1999. Extended-spectrum β-lactamase TEM-4 in Pseudomonas aeruginosa. Clin. Microbiol. Infect. 5:651-652. [DOI] [PubMed] [Google Scholar]
  • 23.Poirel, L., T. Naas, D. Nicolas, L. Collet, S. Bellais, J. D. Cavallo, and P. Nordmann. 2000. Characterization of VIM-2, a carbapenem-hydrolyzing metallo-β-lactamase and its plasmid- and integron-borne gene from a Pseudomonas aeruginosa clinical isolate in France. Antimicrob. Agents Chemother. 44:891-897. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Poirel, L., P. Gerome, C. De Champs, J. Stephanazzi, and P. Nordmann. 2002. Integron-located oxa-32 gene cassette encoding an extended-spectrum variant of OXA-2 β-lactamase from Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 46:566-569. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Poirel, L., D. Girlich, T. Naas, and P. Nordmann. 2001. OXA-28, an extended-spectrum variant of OXA-10 β-lactamase from Pseudomonas aeruginosa and its plasmid- and integron-located gene. Antimicrob. Agents Chemother. 45:447-453. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Poirel, L., G. F. Weldhagen, T. Naas, C. De Champs, M. G. Dove, and P. Nordmann. 2001. Characterization of the class A β-lactamase GES-2 from Pseudomonas aeruginosa with increased hydrolysis of imipenem. Antimicrob. Agents Chemother. 45:2965-2968. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Sirot, J. 1996. Detection of extended-spectrum plasmid-mediated β-lactamases by disk diffusion. Clin. Microbiol. Infect. 2(Suppl. 1):35-39. [DOI] [PubMed] [Google Scholar]
  • 28.Spangenberg, C., T. C. Montie, and B. Tümmler. 1998. Structural and functional implications of sequence diversity of Pseudomonas aeruginosa genes oriC, ampC and fliC. Electrophoresis 19:545-550. [DOI] [PubMed] [Google Scholar]
  • 29.Vahaboglu, H., R. Oztürk, G. Aygün, F. Coskunkan, A. Yaman, A. Kaygusuk, H. Leblebicioglu, I. Balik, K. Aydin, and M. Otkun. 1997. Widespread detection of PER-1-type extended-spectrum β-lactamases among nosocomial Acinetobacter and Pseudomonas aeruginosa isolates in Turkey: a nationwide multicenter study. Antimicrob. Agents Chemother. 41:2265-2269. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Versalovic, J., T. Koeuth, and J. R. Lupski. 1991. Distribution of repetitive DNA sequences in eubacteria and application to fingerprinting of bacterial genomes. Nucleic Acids Res. 19:6823-6831. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Vila, J., M. Navia, J. Ruiz, and C. Casals. 1997. Cloning and nucleotide sequence analysis of a gene encoding an OXA-derived β-lactamase in Acinetobacter baumannii. Antimicrob. Agents Chemother. 41:2757-2759. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Walther-Rasmussen, J., A. H. Johnsen, and N. Hoiby. 1999. Terminal truncations in AmpC β-lactamase from a clinical isolate of Pseudomonas aeruginosa. Eur. J. Biochem. 263:478-485. [DOI] [PubMed] [Google Scholar]
  • 33.Watanabe, M., S. Iyobe, M. Inoue, and S. Mitsuhashi. 1991. Transferable imipenem resistance in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 35:147-151. [DOI] [PMC free article] [PubMed] [Google Scholar]

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