1
|
Can inhibitor-resistant substitutions in the Mycobacterium tuberculosis β-Lactamase BlaC lead to clavulanate resistance?: a biochemical rationale for the use of β-lactam-β-lactamase inhibitor combinations. Antimicrob Agents Chemother 2013; 57:6085-96. [PMID: 24060876 DOI: 10.1128/aac.01253-13] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The current emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis calls for novel treatment strategies. Recently, BlaC, the principal β-lactamase of Mycobacterium tuberculosis, was recognized as a potential therapeutic target. The combination of meropenem and clavulanic acid, which inhibits BlaC, was found to be effective against even extensively drug-resistant M. tuberculosis strains when tested in vitro. Yet there is significant concern that drug resistance against this combination will also emerge. To investigate the potential of BlaC to evolve variants resistant to clavulanic acid, we introduced substitutions at important amino acid residues of M. tuberculosis BlaC (R220, A244, S130, and T237). Whereas the substitutions clearly led to in vitro clavulanic acid resistance in enzymatic assays but at the expense of catalytic activity, transformation of variant BlaCs into an M. tuberculosis H37Rv background revealed that impaired inhibition of BlaC did not affect inhibition of growth in the presence of ampicillin and clavulanate. From these data we propose that resistance to β-lactam-β-lactamase inhibitor combinations will likely not arise from structural alteration of BlaC, therefore establishing confidence that this therapeutic modality can be part of a successful treatment regimen against M. tuberculosis.
Collapse
|
2
|
Kinetic and crystallographic studies of extended-spectrum GES-11, GES-12, and GES-14 β-lactamases. Antimicrob Agents Chemother 2012; 56:5618-25. [PMID: 22908160 DOI: 10.1128/aac.01272-12] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
GES-1 is a class A extended-spectrum β-lactamase conferring resistance to penicillins, narrow- and expanded-spectrum cephalosporins, and ceftazidime. However, GES-1 poorly hydrolyzes aztreonam and cephamycins and exhibits very low k(cat) values for carbapenems. Twenty-two GES variants have been discovered thus far, differing from each other by 1 to 3 amino acid substitutions that affect substrate specificity. GES-11 possesses a Gly243Ala substitution which seems to confer to this variant an increased activity against aztreonam and ceftazidime. GES-12 differs from GES-11 by a single Thr237Ala substitution, while GES-14 differs from GES-11 by the Gly170Ser mutation, which is known to confer increased carbapenemase activity. GES-11 and GES-12 were kinetically characterized and compared to GES-1 and GES-14. Purified GES-11 and GES-12 showed strong activities against most tested β-lactams, with the exception of temocillin, cefoxitin, and carbapenems. Both variants showed a significantly increased rate of hydrolysis of cefotaxime, ceftazidime, and aztreonam. On the other hand, GES-11 and GES-12 (and GES-14) variants all containing Ala243 exhibited increased susceptibility to classical inhibitors. The crystallographic structures of the GES-11 and GES-14 β-lactamases were solved. The overall structures of GES-11 and GES-14 are similar to that of GES-1. The Gly243Ala substitution caused only subtle local rearrangements, notably in the typical carbapenemase disulfide bond. The active sites of GES-14 and GES-11 are very similar, with the Gly170Ser substitution leading only to the formation of additional hydrogen bonds of the Ser residue with hydrolytic water and the Glu166 residue.
Collapse
|
3
|
Roles of residues Cys69, Asn104, Phe160, Gly232, Ser237, and Asp240 in extended-spectrum beta-lactamase Toho-1. Antimicrob Agents Chemother 2010; 55:284-90. [PMID: 21078949 DOI: 10.1128/aac.00098-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Toho-1, which is also designated CTX-M-44, is an extended-spectrum class A β-lactamase that has high activity toward cefotaxime. In this study, we investigated the roles of residues suggested to be critical for the substrate specificity expansion of Toho-1 in previous structural analyses. Six amino acid residues were replaced one by one with amino acids that are often observed in the corresponding position of non-extended-spectrum β-lactamases. The mutants produced in Escherichia coli strains were analyzed both for their kinetic properties and their effect on drug susceptibilities. The results indicate that the substitutions of Asn104 and Ser237 have certain effects on expansion of substrate specificity, while those of Cys69 and Phe160 have less effect, and that of Asp240 has no effect on the hydrolysis of any substrates tested. Gly232, which had been assumed to increase the flexibility of the substrate binding site, was revealed not to be critical for the expansion of substrate specificity of this enzyme, although this substitution resulted in deleterious effects on expression and stability of the enzyme.
Collapse
|
4
|
Substrate selectivity and a novel role in inhibitor discrimination by residue 237 in the KPC-2 beta-lactamase. Antimicrob Agents Chemother 2010; 54:2867-77. [PMID: 20421396 DOI: 10.1128/aac.00197-10] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Beta-lactamase-mediated antibiotic resistance continues to challenge the contemporary treatment of serious bacterial infections. The KPC-2 beta-lactamase, a rapidly emerging gram-negative resistance determinant, hydrolyzes all commercially available beta-lactams, including carbapenems and beta-lactamase inhibitors; the amino acid sequence requirements responsible for this versatility are not yet known. To explore the bases of beta-lactamase activity, we conducted site saturation mutagenesis at Ambler position 237. Only the T237S variant of the KPC-2 beta-lactamase expressed in Escherichia coli DH10B maintained MICs equivalent to those of the wild type (WT) against all of the beta-lactams tested, including carbapenems. In contrast, the T237A variant produced in E. coli DH10B exhibited elevated MICs for only ampicillin, piperacillin, and the beta-lactam-beta-lactamase inhibitor combinations. Residue 237 also plays a novel role in inhibitor discrimination, as 11 of 19 variants exhibit a clavulanate-resistant, sulfone-susceptible phenotype. We further showed that the T237S variant displayed substrate kinetics similar to those of the WT KPC-2 enzyme. Consistent with susceptibility testing, the T237A variant demonstrated a lower k(cat)/K(m) for imipenem, cephalothin, and cefotaxime; interestingly, the most dramatic reduction was with cefotaxime. The decreases in catalytic efficiency were driven by both elevated K(m) values and decreased k(cat) values compared to those of the WT enzyme. Moreover, the T237A variant manifested increased K(i)s for clavulanic acid, sulbactam, and tazobactam, while the T237S variant displayed K(i)s similar to those of the WT. To explain these findings, a molecular model of T237A was constructed and this model suggested that (i) the hydroxyl side chain of T237 plays an important role in defining the substrate profile of the KPC-2 beta-lactamase and (ii) hydrogen bonding between the hydroxyl side chain of T237 and the sp(2)-hybridized carboxylate of imipenem may not readily occur in the T237A variant. This stringent requirement for selected cephalosporinase and carbapenemase activity and the important role of T237 in inhibitor discrimination in KPC-2 are central considerations in the future design of beta-lactam antibiotics and inhibitors.
Collapse
|
5
|
Fenollar-Ferrer C, Frau J, Donoso J, Muñoz F. Evolution of class C β-lactamases: factors influencing their hydrolysis and recognition mechanisms. Theor Chem Acc 2008. [DOI: 10.1007/s00214-008-0463-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
6
|
Sauvage E, Fonzé E, Quinting B, Galleni M, Frère JM, Charlier P. Crystal structure of the Mycobacterium fortuitum class A beta-lactamase: structural basis for broad substrate specificity. Antimicrob Agents Chemother 2006; 50:2516-21. [PMID: 16801434 PMCID: PMC1489783 DOI: 10.1128/aac.01226-05] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
beta-Lactamases are the main cause of bacterial resistance to penicillins and cephalosporins. Class A beta-lactamases, the largest group of beta-lactamases, have been found in many bacterial strains, including mycobacteria, for which no beta-lactamase structure has been previously reported. The crystal structure of the class A beta-lactamase from Mycobacterium fortuitum (MFO) has been solved at 2.13-A resolution. The enzyme is a chromosomally encoded broad-spectrum beta-lactamase with low specific activity on cefotaxime. Specific features of the active site of the class A beta-lactamase from M. fortuitum are consistent with its specificity profile. Arg278 and Ser237 favor cephalosporinase activity and could explain its broad substrate activity. The MFO active site presents similarities with the CTX-M type extended-spectrum beta-lactamases but lacks a specific feature of these enzymes, the VNYN motif (residues 103 to 106), which confers on CTX-M-type extended-spectrum beta-lactamases a more efficient cefotaximase activity.
Collapse
Affiliation(s)
- Eric Sauvage
- Centre d'Ingénierie des Protéines, Université de Liège, Institut de Physique B5, B-4000 Liège, Belgium.
| | | | | | | | | | | |
Collapse
|
7
|
Chen Y, Delmas J, Sirot J, Shoichet B, Bonnet R. Atomic resolution structures of CTX-M beta-lactamases: extended spectrum activities from increased mobility and decreased stability. J Mol Biol 2005; 348:349-62. [PMID: 15811373 DOI: 10.1016/j.jmb.2005.02.010] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2004] [Revised: 01/28/2005] [Accepted: 02/02/2005] [Indexed: 11/30/2022]
Abstract
Extended spectrum beta-lactamases (ESBLs) confer bacterial resistance to third-generation cephalosporins, such as cefotaxime and ceftazidime, increasing hospital mortality rates. Whereas these antibiotics are almost impervious to classic beta-lactamases, such as TEM-1, ESBLs have one to four orders greater activity against them. The origins of this activity have been widely studied for the TEM and SHV-type ESBLs, but have received less attention for the CTX-M beta-lactamases, an emerging family that is now the dominant ESBL in several regions. To understand how CTX-M beta-lactamases achieve their remarkable activity, biophysical and structural studies were undertaken. Using reversible, two-state thermal denaturation, it was found that as these enzymes evolve a broader substrate range, they sacrifice stability. Thus, the mutant enzyme CTX-M-16 is eightfold more active against ceftazidime than the pseudo-wild-type CTX-M-14 but is 1.9 kcal/mol less stable. This is consistent with a "stability-activity tradeoff," similar to that observed in the evolution of other resistance enzymes. To investigate the structural basis of enzyme activity and stability, the structures of four CTX-M enzymes were determined by X-ray crystallography. The structures of CTX-M-14, CTX-M-27, CTX-M-9 and CTX-M-16 were determined to 1.10 Angstroms, 1.20 Angstroms, 0.98 Angstroms and 1.74 Angstroms resolution, respectively. The enzyme active sites resemble those of the narrow-spectrum TEM-1 and SHV-1, and not the enlarged sites typical of ESBL mutants such as TEM-52 and TEM-64. Instead, point substitutions leading to specific interactions may be responsible for the improved activity against ceftazidime and cefotaxime, consistent with observations first made for the related Toho-1 enzyme. The broadened substrate range of CTX-M-16 may result from coupled defects in the enzyme's B3 strand, which lines the active site. Substitutions Val231-->Ala and Asp240-->Gly, which convert CTX-M-14 into CTX-M-16, occur at either end of this strand. These defects appear to increase the mobility of B3 based on anisotropic B-factor analyses at ultrahigh resolution, consistent with stability loss and activity gain. The unusually high resolution of these structures that makes such analyses possible also makes them good templates for inhibitor discovery.
Collapse
Affiliation(s)
- Yu Chen
- Department of Pharmaceutical Chemistry, University of California, San Francisco, Genentech Hall, 600 16th Street, San Francisco, CA 94143-2240, USA
| | | | | | | | | |
Collapse
|
8
|
Shimamura T, Ibuka A, Fushinobu S, Wakagi T, Ishiguro M, Ishii Y, Matsuzawa H. Acyl-intermediate structures of the extended-spectrum class A beta-lactamase, Toho-1, in complex with cefotaxime, cephalothin, and benzylpenicillin. J Biol Chem 2002; 277:46601-8. [PMID: 12221102 DOI: 10.1074/jbc.m207884200] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bacterial resistance to beta-lactam antibiotics is a serious problem limiting current clinical therapy. The most common form of resistance is the production of beta-lactamases that inactivate beta-lactam antibiotics. Toho-1 is an extended-spectrum beta-lactamase that has acquired efficient activity not only to penicillins but also to cephalosporins including the expanded-spectrum cephalosporins that were developed to be stable in former beta-lactamases. We present the acyl-intermediate structures of Toho-1 in complex with cefotaxime (expanded-spectrum cephalosporin), cephalothin (non-expanded-spectrum cephalosporin), and benzylpenicillin at 1.8-, 2.0-, and 2.1-A resolutions, respectively. These structures reveal distinct features that can explain the ability of Toho-1 to hydrolyze expanded-spectrum cephalosporins. First, the Omega-loop of Toho-1 is displaced to avoid the steric contacts with the bulky side chain of cefotaxime. Second, the conserved residues Asn(104) and Asp(240) form unique interactions with the bulky side chain of cefotaxime to fix it tightly. Finally, the unique interaction between the conserved Ser(237) and cephalosporins probably helps to bring the beta-lactam carbonyl group to the suitable position in the oxyanion hole, thus increasing the cephalosporinase activity.
Collapse
Affiliation(s)
- Tatsuro Shimamura
- Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | | | | | | | | | | | | |
Collapse
|
9
|
Morin AS, Poirel L, Mory F, Labia R, Nordmann P. Biochemical-genetic analysis and distribution of DES-1, an Ambler class A extended-spectrum beta-lactamase from Desulfovibrio desulfuricans. Antimicrob Agents Chemother 2002; 46:3215-22. [PMID: 12234847 PMCID: PMC128801 DOI: 10.1128/aac.46.10.3215-3222.2002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Desulfovibrio spp. are gram-negative anaerobes phylogenetically related to Bacteroides spp., which are rarely isolated and which are mostly isolated from intra-abdominal abscesses. Desulfovibrio desulfuricans clinical isolate D3 had a clavulanic acid-inhibited beta-lactam resistance profile and was resistant to some expanded-spectrum cephalosporins. A beta-lactamase gene, bla(DES-1), was cloned from whole-cell DNA of isolate D3 and expressed in Escherichia coli. Purified beta-lactamase DES-1, with a pI value of 9.1, had a relative molecular mass of ca. 31 kDa and a mature protein of 288 amino acids. DES-1 was distantly related to Ambler class A beta-lactamases and most closely related to PenA from Burkholderia pseudomallei (48% amino acid identity). It was weakly related to class A beta-lactamases CblA, CepA, CfxA, and CfxA2 from other anaerobic species, Bacteroides spp. and Prevotella intermedia. Its hydrolysis spectrum included amino- and ureidopenicillins, narrow-spectrum cephalosporins, ceftriaxone, and cefoperazone. bla(DES-1)-like genes were not identified in phylogenetically related Desulfovibrio fairfieldensis isolates. However, they were found in some but not all D. desulfuricans strains, thus suggesting that these genes may be present in a given D. desulfuricans subspecies.
Collapse
Affiliation(s)
- Anne-Sophie Morin
- Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France
| | | | | | | | | |
Collapse
|
10
|
Nukaga M, Mayama K, Crichlow GV, Knox JR. Structure of an extended-spectrum class A beta-lactamase from Proteus vulgaris K1. J Mol Biol 2002; 317:109-17. [PMID: 11916382 DOI: 10.1006/jmbi.2002.5420] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The structure of a chromosomal extended-spectrum beta-lactamase (ESBL) having the ability to hydrolyze cephalosporins including cefuroxime and ceftazidime has been determined by X-ray crystallography to 1.75 A resolution. The species-specific class A beta-lactamase from Proteus vulgaris K1 was crystallized at pH 6.25 and its structure solved by molecular replacement. Refinement of the model resulted in crystallographic R and R(free) of 16.9 % and 19.3 %, respectively. The folding of the K1 enzyme is broadly similar to that of non-ESBL TEM-type beta-lactamases (2 A rmsd for C(alpha)) and differs by only 0.35 A for all atoms of six conserved residues in the catalytic site. Other residues promoting extended-spectrum activity in K1 include the side-chains of atypical residues Ser237 and Lys276. These side-chains are linked by two water molecules, one of which lies in the position normally filled by the guanidinium group of Arg244, present in most non-ESBL enzymes but absent from K1. The ammonium group of Lys276, ca 3.5 A from the virtual Arg244 guanidinium position, may interact with polar R2 substitutents on the dihydrothiazene ring of cephalosporins.
Collapse
Affiliation(s)
- Michiyoshi Nukaga
- Department of Molecular and Cell Biology, The University of Connecticut, Storrs, CT 06269-3125, USA
| | | | | | | |
Collapse
|
11
|
Liassine N, Madec S, Ninet B, Metral C, Fouchereau-Peron M, Labia R, Auckenthaler R. Postneurosurgical meningitis due to Proteus penneri with selection of a ceftriaxone-resistant isolate: analysis of chromosomal class A beta-lactamase HugA and its LysR-type regulatory protein HugR. Antimicrob Agents Chemother 2002; 46:216-9. [PMID: 11751137 PMCID: PMC126972 DOI: 10.1128/aac.46.1.216-219.2002] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We report on a case of a postneurosurgical meningitis due to ceftriaxone-susceptible Proteus penneri, with selection of a ceftriaxone-resistant isolate following treatment with ceftriaxone. The isolates presented identical patterns by pulsed-field gel electrophoresis and produced a single beta-lactamase named HugA with an isoelectric point of 6.7. The ceftriaxone-resistant isolate hyperproduced the beta-lactamase (increase in the level of production, about 90-fold). The sequences of the hugA beta-lactamase gene and its regulator, hugR, were identical in both P. penneri strains and had 85.96% homology with those of Proteus vulgaris. The HugA beta-lactamase belongs to molecular class A, and the transcriptional regulator HugR belongs to the LysR family.
Collapse
Affiliation(s)
- Nadia Liassine
- Central Laboratory of Bacteriology, University Hospital, Geneva, Switzerland.
| | | | | | | | | | | | | |
Collapse
|
12
|
Decousser JW, Poirel L, Nordmann P. Characterization of a chromosomally encoded extended-spectrum class A beta-lactamase from Kluyvera cryocrescens. Antimicrob Agents Chemother 2001; 45:3595-8. [PMID: 11709346 PMCID: PMC90875 DOI: 10.1128/aac.45.12.3595-3598.2001] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A chromosomally located beta-lactamase gene, cloned and expressed in Escherichia coli from a reference strain of the enterobacterial species Kluyvera cryocrescens, encoded a clavulanic acid-inhibited Ambler class A enzyme, KLUC-1, with a pI value of 7.4. KLUC-1 shared 86% amino acid identity with a subgroup of plasmid-mediated CTX-M-type extended-spectrum beta-lactamases (CTX-M-1, -3, -10, -11, and -12), the most closely related enzymes, and 77% amino acid identity with KLUA-1 from Kluyvera ascorbata. The substrate profile of KLUC-1 corresponded to that of CTX-M-type enzymes.
Collapse
Affiliation(s)
- J W Decousser
- Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France
| | | | | |
Collapse
|
13
|
Bellais S, Poirel L, Fortineau N, Decousser JW, Nordmann P. Biochemical-genetic characterization of the chromosomally encoded extended-spectrum class A beta-lactamase from Rahnella aquatilis. Antimicrob Agents Chemother 2001; 45:2965-8. [PMID: 11557504 PMCID: PMC90766 DOI: 10.1128/aac.45.10.2965-2968.2001] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
From whole-cell DNA of a clinical isolate of the enterobacterial species Rahnella aquatilis, a beta-lactamase gene was cloned that encoded a chromosomally encoded Ambler class A enzyme, RAHN-1. RAHN-1, with a pI of 7.2, shares 76, 73, and 71% amino acid identity with the extended-spectrum beta-lactamase of chromosomal origin from Serratia fonticola and with the plasmid-mediated beta-lactamases CTX-M-2 and CTX-M-1, respectively. The hydrolysis spectrum of the clavulanic acid-inhibited RAHN-1 was expanded to cephalosporins such as cefuroxime, cefotaxime, and ceftriaxone, but not to ceftazidime. Its expression was not inducible.
Collapse
Affiliation(s)
- S Bellais
- Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 78 rue de Général Leclerc, 94275 Le Kremlin-Bicêtre Cedex, France
| | | | | | | | | |
Collapse
|
14
|
Oliver A, Pérez-Díaz JC, Coque TM, Baquero F, Cantón R. Nucleotide sequence and characterization of a novel cefotaxime-hydrolyzing beta-lactamase (CTX-M-10) isolated in Spain. Antimicrob Agents Chemother 2001; 45:616-20. [PMID: 11158766 PMCID: PMC90338 DOI: 10.1128/aac.45.2.616-620.2001] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A cefotaxime-resistant, ceftazidime-susceptible Escherichia coli isolate was obtained from a patient with sepsis in 1997, from which a beta-lactamase with a pI of 8.1 was cloned. Cephaloridine and cefotaxime relative hydrolysis rates were 167 and 81, respectively (penicillin G rate = 100), whereas ceftazidime hydrolysis was not detected. The nucleotide sequence revealed a bla gene related to that coding for CTX-M-3. Despite 21 nucleotide substitutions, only 2 determined amino acid changes (Ala27Val and Arg38Gln). The amino acid sequence identity between this enzyme, designated CTX-M-10, and the chromosomal beta-lactamase of Kluyvera ascorbata was 81%.
Collapse
Affiliation(s)
- A Oliver
- Servicio de Microbiología, Hospital Ramón y Cajal, Madrid, Spain
| | | | | | | | | |
Collapse
|
15
|
Giakkoupi P, Tzouvelekis LS, Tsakris A, Loukova V, Sofianou D, Tzelepi E. IBC-1, a novel integron-associated class A beta-lactamase with extended-spectrum properties produced by an Enterobacter cloacae clinical strain. Antimicrob Agents Chemother 2000; 44:2247-53. [PMID: 10952563 PMCID: PMC90053 DOI: 10.1128/aac.44.9.2247-2253.2000] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A transferable beta-lactamase produced by a multidrug-resistant clinical isolate of Enterobacter cloacae was studied. The bla gene was carried by a large (>80-kb) transmissible plasmid. Nucleotide sequence analysis of cloned fragments revealed that it was part of a gene cassette carried by a class 1 integron along with other resistance genes, including aac(6')-Ib. The encoded beta-lactamase, designated IBC-1, was a novel class A enzyme that hydrolyzed ceftazidime and cefotaxime and was inhibited by tazobactam and, to a lesser extent, by clavulanate. Also, imipenem exhibited potent inhibitory activity against IBC-1. The enzyme consisted of 287 amino acid residues, including Ser-237, cysteines at positions 69 and 237a, and Arg-244, which may be implicated in its interaction with beta-lactams. In amino acid sequence comparisons, IBC-1 displayed the highest similarity with the chromosomal penicillinase of Yersinia enterocolitica, a carbenicillinase from Proteus mirabilis GN79, the species-specific beta-lactamases of Klebsiella oxytoca, and the carbapenemase Sme-1. However, a phylogenetic association with established beta-lactamase clusters could not be conclusively shown.
Collapse
Affiliation(s)
- P Giakkoupi
- Department of Bacteriology, Hellenic Pasteur Institute, Greece
| | | | | | | | | | | |
Collapse
|
16
|
Alvarez-Idaboy J, González-Jonte R, Hernández-Laguna A, Smeyers Y. Reaction mechanism of the acyl-enzyme formation in β-lactam hydrolysis by means of quantum chemical modeling. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s0166-1280(00)00351-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
17
|
Tzouvelekis LS, Tzelepi E, Tassios PT, Legakis NJ. CTX-M-type beta-lactamases: an emerging group of extended-spectrum enzymes. Int J Antimicrob Agents 2000; 14:137-42. [PMID: 10720804 DOI: 10.1016/s0924-8579(99)00165-x] [Citation(s) in RCA: 190] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
CTX-M-type beta-lactamases constitute a novel group of class A beta-lactamases with extended-spectrum properties. They are encoded by transferable plasmids and found in various enterobacteria, mostly Salmonella typhimurium, Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis. CTX-M enzymes share extensive sequence similarity with the chromosomal beta-lactamases of Klebsiella oxytoca. They efficiently hydrolyze many newer broad-spectrum oximino-beta-lactams including cefotaxime, ceftriaxone and aztreonam and are readily inhibited by tazobactam and clavulanate. CTX-M-producing enterobacteria are endemic in Latin America and in some areas of North Eastern Europe. Data on their structure, properties and epidemiology are discussed.
Collapse
Affiliation(s)
- L S Tzouvelekis
- Department of Microbiology, Medical School, National University of Athens, M. Asias 75, Athens, Greece
| | | | | | | |
Collapse
|
18
|
Ohno A, Ishii Y, Ma L, Yamaguchi K. Problems related to determination of MICs of oximino-type expanded-spectrum cephems for Proteus vulgaris. J Clin Microbiol 2000; 38:677-81. [PMID: 10655366 PMCID: PMC86174 DOI: 10.1128/jcm.38.2.677-681.2000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During in vitro susceptibility testing of clinical isolates of Proteus vulgaris, we noted that the MICs of several expanded-spectrum cephems were much higher in the broth microdilution method than in the agar dilution method (termed the MIC gap phenomenon). Here we investigated the mechanism of the MIC gap phenomenon. Cephems with the MIC gap phenomenon were of the oximino type, such as cefotaxime, cefteram, and cefpodoxime, which serve as good substrates for inducible class A beta-lactamase (CumA) enzymes produced by P. vulgaris; this finding suggests a relationship between the MIC gap phenomenon and CumA. Since peptidoglycan recycling shares a system common to that inducing CumA, we analyzed the mechanism of the MIC gap phenomenon using P. vulgaris B317 and isogenic mutants with mutations in the peptidoglycan recycling and beta-lactamase induction systems. The MIC gap phenomenon was observed in the parent strain B317 but not in B317G (cumG-defective mutant; defective peptidoglycan recycling) and B317R (cumR-defective mutant; defective CumA transcriptional regulator). No beta-lactamase activity was detected in B317G and B317R. beta-Lactamase activity and the MIC gap phenomenon were restored in B317G/pMD301 (strain transcomplemented by a cloned cumG gene) and B317R/pMD501 (strain transcomplemented by a cloned cumR gene). MICs determined by the agar dilution method increased when lower agar concentrations were used. Our results indicated that the mechanism of the MIC gap phenomenon is related to peptidoglycan recycling and CumA induction systems. However, it remains unclear how beta-lactamase induction of P. vulgaris is suppressed on agar plates.
Collapse
Affiliation(s)
- A Ohno
- Department of Microbiology, Toho University School of Medicine, Ota-ku, Tokyo, Japan.
| | | | | | | |
Collapse
|
19
|
Sougakoff W, Naas T, Nordmann P, Collatz E, Jarlier V. Role of ser-237 in the substrate specificity of the carbapenem-hydrolyzing class A beta-lactamase Sme-1. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1433:153-8. [PMID: 10446368 DOI: 10.1016/s0167-4838(99)00138-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The role of the serine residue found at position 237 in the carbapenemase Sme-1 has been investigated by constructing a mutant in which Ser-237 was replaced by an alanine. The S237A mutant showed a catalytic behavior against penicillins and aztreonam very similar to that of Sme-1. By contrast, S237A was characterized by a reduced catalytic efficiency against cephems, such as cephalothin and cephaloridine. In addition, the weak activity of Sme-1 against the cephamycin cefoxitin was hardly detectable with the mutant enzyme. Finally, the Ser-237-->Ala mutation resulted in a marked decrease in catalytic activity against imipenem, showing that Ser-237 contributes to the carbapenemase activity of the class A beta-lactamase Sme-1.
Collapse
Affiliation(s)
- W Sougakoff
- Laboratoire de Recherche Moléculaire sur les Antibiotiques (LRMA), Faculté de Médecine Pitié-Salpêtrière, Université Pierre et Marie Curie, 91 boulevard de l'Hôpital, F-75634, Paris Cedex 13, Paris, France.
| | | | | | | | | |
Collapse
|
20
|
Bouthors AT, Delettré J, Mugnier P, Jarlier V, Sougakoff W. Site-directed mutagenesis of residues 164, 170, 171, 179, 220, 237 and 242 in PER-1 beta-lactamase hydrolysing expanded-spectrum cephalosporins. PROTEIN ENGINEERING 1999; 12:313-8. [PMID: 10325401 DOI: 10.1093/protein/12.4.313] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The class A beta-lactamase PER-1, which displays 26% identity with the TEM-type extended-spectrum beta-lactamases (ESBLs), is characterized by a substrate profile similar to that conferred by these latter enzymes. The role of residues Ala164, His170, Ala171, Asn179, Arg220, Thr237 and Lys242, found in PER-1, was assessed by site-directed mutagenesis. Replacement of Ala164 by Arg yielded an enzyme with no detectable beta-lactamase activity. Two other mutants, N179D and A164R+N179D, were also inactive. Conversely, a mutant with the A171E substitution displayed a substrate profile very similar to that of the wild-type enzyme. Moreover, the replacement of Ala171 by Glu in the A164R enzyme yielded a double mutant which was active, suggesting that Glu171 could compensate for the deleterious effect of Arg164 in the A164R+A171E enzyme. A specific increase in kcat for cefotaxime was observed with H170N, whereas R220L and T237A displayed a specific decrease in activity towards the same drug and a general increase in affinity towards cephalosporins. Finally, the K242E mutant displayed a kinetic behaviour very similar to that of PER-1. Based on three-dimensional models generated by homology modelling and molecular dynamics, these results suggest novel structure-activity relationships in PER-1, when compared with those previously described for the TEM-type ESBLs.
Collapse
Affiliation(s)
- A T Bouthors
- Laboratoire de Recherche Moléculaire sur les Antibiotiques, Université Pierre et Marie Curie (Paris VI), Faculté de Médecine Pitié-Salpêtrière, F-75634 Paris cedex 13, France
| | | | | | | | | |
Collapse
|
21
|
Ibuka A, Taguchi A, Ishiguro M, Fushinobu S, Ishii Y, Kamitori S, Okuyama K, Yamaguchi K, Konno M, Matsuzawa H. Crystal structure of the E166A mutant of extended-spectrum beta-lactamase Toho-1 at 1.8 A resolution. J Mol Biol 1999; 285:2079-87. [PMID: 9925786 DOI: 10.1006/jmbi.1998.2432] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bacterial resistance to beta-lactams is mainly due to the production of beta-lactamase. Especially through the production of extended-spectrum beta-lactamases (ESBLs), bacteria have acquired resistance not only to penicillins, but also to expanded-spectrum cephems. Here, we describe the crystal structure of the E166A mutant of class A beta-lactamase Toho-1 at 1.8 A resolution, the first reported tertiary structure of an ESBL. Instead of the wild-type enzyme, a mutant Toho-1, in which Glu166 was replaced with alanine, was used for this study, because of the strong tendency of the wild-type enzyme to form twinned crystals. The overall structure of Toho-1 is similar to the crystal structures of non-ESBLs, with no pronounced backbone rearrangement of the framework. However, there are some notable local changes. First, a difference in the disposition of an arginine residue, which is at position 244 in non-ESBLs but at position 276 in Toho-1 and other ESBLs, was revealed and the role of this arginine residue is discussed. Moreover, changes in the hydrogen-bonding pattern and in the formation of the hydrophobic core were also observed near the Omega loop. In particular, the lack of hydrogen bonds in the vicinity of the Omega loop could be a cause of the extended substrate specificity of Toho-1. Through the generation of a model for the enzyme-substrate complex, a conformational change of Toho-1 occurring on complex formation is discussed based on the active-site cleft structure and the substrate profile.
Collapse
Affiliation(s)
- A Ibuka
- Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Blázquez J, Negri MC, Morosini MI, Gómez-Gómez JM, Baquero F. A237T as a modulating mutation in naturally occurring extended-spectrum TEM-type beta-lactamases. Antimicrob Agents Chemother 1998; 42:1042-4. [PMID: 9593123 PMCID: PMC105741 DOI: 10.1128/aac.42.5.1042] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A TEM-1 beta-lactamase derivative containing the single amino acid substitution A237T slightly increased (from 24 to 32 microg/ml) the cephalothin MIC for Escherichia coli RYC1000 but did not influence the activities of cefotaxime, ceftazidime, and aztreonam (MICs of 0.03, 0.12, and 0.06 microg/ml, respectively). Despite its apparent neutrality, addition of the A237T mutation to the pair of mutations characterizing TEM-10 (R164S and E240K) had a strong effect on substrate preference. Ceftazidime and aztreonam MICs decreased from 128 and 16 microg/ml to 16 and 2 microg/ml, respectively. In contrast, the cefotaxime MIC increased from 0.5 to 4 microg/ml. The acquisition of apparently neutral or even deleterious mutations results in a very effective mechanism of resistance to different beta-lactams that may be simultaneously or subsequently present in the environment. We propose here that the mutation in position 237 is an example of a modulating mutation and that consideration of this type of mutation may be important for understanding the evolution of beta-lactamases.
Collapse
Affiliation(s)
- J Blázquez
- Servicio de Microbiología, Hospital Ramón y Cajal, Madrid, Spain.
| | | | | | | | | |
Collapse
|
23
|
Gazouli M, Tzelepi E, Sidorenko SV, Tzouvelekis LS. Sequence of the gene encoding a plasmid-mediated cefotaxime-hydrolyzing class A beta-lactamase (CTX-M-4): involvement of serine 237 in cephalosporin hydrolysis. Antimicrob Agents Chemother 1998; 42:1259-62. [PMID: 9593162 PMCID: PMC105797 DOI: 10.1128/aac.42.5.1259] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The sequence of the gene encoding a novel cefotaxime-hydrolyzing beta-lactamase (CTX-M-4) was determined. It was located in a plasmid harbored by a Salmonella typhimurium strain. CTX-M-4 was similar to the plasmidic cefotaxime-hydrolyzing beta-lactamases CTX-M-2 and Toho-1 and related to the chromosomal beta-lactamase of Klebsiella oxytoca. A Ser-237-->Ala substitution, introduced by site-directed mutagenesis, caused minor alterations in the interaction of CTX-M-4 with beta-lactams, reducing slightly the relative hydrolytic activity against cefotaxime and the susceptibility to inhibition by clavulanate.
Collapse
Affiliation(s)
- M Gazouli
- Department of Bacteriology, Hellenic Pasteur Institute, Athens, Greece
| | | | | | | |
Collapse
|
24
|
Matagne A, Lamotte-Brasseur J, Frère JM. Catalytic properties of class A beta-lactamases: efficiency and diversity. Biochem J 1998; 330 ( Pt 2):581-98. [PMID: 9480862 PMCID: PMC1219177 DOI: 10.1042/bj3300581] [Citation(s) in RCA: 292] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
beta-Lactamases are the main cause of bacterial resistance to penicillins, cephalosporins and related beta-lactam compounds. These enzymes inactivate the antibiotics by hydrolysing the amide bond of the beta-lactam ring. Class A beta-lactamases are the most widespread enzymes and are responsible for numerous failures in the treatment of infectious diseases. The introduction of new beta-lactam compounds, which are meant to be 'beta-lactamase-stable' or beta-lactamase inhibitors, is thus continuously challenged either by point mutations in the ubiquitous TEM and SHV plasmid-borne beta-lactamase genes or by the acquisition of new genes coding for beta-lactamases with different catalytic properties. On the basis of the X-ray crystallography structures of several class A beta-lactamases, including that of the clinically relevant TEM-1 enzyme, it has become possible to analyse how particular structural changes in the enzyme structures might modify their catalytic properties. However, despite the many available kinetic, structural and mutagenesis data, the factors explaining the diversity of the specificity profiles of class A beta-lactamases and their amazing catalytic efficiency have not been thoroughly elucidated. The detailed understanding of these phenomena constitutes the cornerstone for the design of future generations of antibiotics.
Collapse
Affiliation(s)
- A Matagne
- Centre for Protein Engineering and Laboratoire d'Enzymologie, Université de Liège, Institut de Chimie B6, 4000 Liège (Sart Tilman), Belgium
| | | | | |
Collapse
|
25
|
Péduzzi J, Farzaneh S, Reynaud A, Barthélémy M, Labia R. Characterization and amino acid sequence analysis of a new oxyimino cephalosporin-hydrolyzing class A beta-lactamase from Serratia fonticola CUV. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1341:58-70. [PMID: 9300809 DOI: 10.1016/s0167-4838(97)00020-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Serratia fonticola CUV produces two isoenzymes (forms I and II) with beta-lactamase activity which were purified by a five-step procedure. The isoenzymes had identical kinetic parameters and isoelectric point (pI = 8.12). They were characterized by a specific activity towards benzylpenicillin of 1650 U/mg. The beta-lactamase hydrolyzed benzylpenicillin, amoxycillin, ureidopenicillins, first- and second-generation cephalosporins. Carboxypenicillins and isoxazolylpenicillins were hydrolyzed to a lesser extent. Towards cefotaxime and ceftriaxone (third-generation cephalosporins), the S. fonticola enzyme exhibited catalytic efficiencies much higher than those of MEN-1 and extended-spectrum TEM derivative beta-lactamases. The beta-lactamase from S. fonticola was markedly inhibited by beta-lactamase inhibitors such as clavulanic acid, sulbactam and tazobactam. The purified isoenzymes were digested by trypsin, endoproteinase Asp-N and chymotrypsin. Amino acid sequence determinations of the resulting peptides allowed the alignment of 267 amino acid residues (Swiss-Prot, accession number P 80545) for form I beta-lactamase. Form II is five residues shorter than form I at its N-terminus. From amino acid sequence comparisons, S. fonticola CUV beta-lactamase was found to share more than 69.3% identity with the chromosomally encoded beta-lactamases of Klebsiella oxytoca, Proteus vulgaris, Citrobacter diversus and the plasmid-mediated enzymes MEN-1 and Toho-1. Therefore, the oxyimino cephalosporin-hydrolyzing beta-lactamase of S. fonticola belongs to Ambler's class A. Contribution of the serine at ABL 237 in the broad-spectrum activity of these beta-lactamases is discussed.
Collapse
Affiliation(s)
- J Péduzzi
- Muséum National Histoire Naturelle, CNRS URA 401, IFR 63, Paris, France.
| | | | | | | | | |
Collapse
|
26
|
Hosseini-Mazinani SM, Nakajima E, Ihara Y, Kameyama KZ, Sugimoto K. Recovery of active beta-lactamases from Proteus vulgaris and RTEM-1 hybrid by random mutagenesis by using a dnaQ strain of Escherichia coli. Antimicrob Agents Chemother 1996; 40:2152-9. [PMID: 8878598 PMCID: PMC163490 DOI: 10.1128/aac.40.9.2152] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Proteus vulgaris and RTEM-1 beta-lactamases that belong to molecular class A with 37% amino acid similarity were examined to find the relationship between amino acid residues and activity of enzymes. MICs of ampicillin were > 2,000 micrograms/ml for Escherichia coli cells producing these enzymes. We have made 18 hybrid genes by substituting the coding region of the P. vulgaris beta-lactamase gene with the equivalent portions from the RTEM-1 gene. Most of these hybrids produced inactive proteins, but a few hybrid enzymes had partial or trace activity. From one of the hybrid genes (MIC of ampicillin, 100 micrograms/ml), we recovered three kinds of active mutants which provided ampicillin MICs of 1,000 micrograms/ml by the selection of spontaneous mutations in a dnaQ strain of E. coli. In these mutants, Leu-148, Met-182, and Tyr-274 were replaced with Val, Thr, and His, respectively. These amino acids have not been identified as residues with functional roles in substrate hydrolysis. Furthermore, from these hybrid mutants, we obtained a second set of mutants which conferred ampicillin MICs of 1,500 micrograms/ml. Interestingly, the second mutations were limited to these three amino acid substitutions. These amino acid residues which do not directly interact with substrates have an effect on enzyme activity. These mutant enzymes exhibited lower K(m) values for cephaloridine than both parental enzymes.
Collapse
|
27
|
Fournier B, Roy PH, Lagrange PH, Philippon A. Chromosomal beta-lactamase genes of Klebsiella oxytoca are divided into two main groups, blaOXY-1 and blaOXY-2. Antimicrob Agents Chemother 1996; 40:454-9. [PMID: 8834897 PMCID: PMC163133 DOI: 10.1128/aac.40.2.454] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The chromosomally encoded beta-lactamase gene (blaOXY-2) of the wild-type Klebsiella oxytoca SL911 was cloned and sequenced. Its nucleotide sequence similarity with the previously sequenced K. oxytoca beta-lactamase gene (blaOXY-1) (Y. Arakawa, M. Ohta, N. Kido, M. Mori, H. Ito, T. Komatsu, Y. Fujii, and N. Kato, Antimicrob. Agents Chemother. 33:63-70, 1989) is 87.3%, and its amino acid similarity is 89.7%. This group of K. oxytoca beta-lactamases is related to chromosomal beta-lactamases of Citrobacter diversus, Proteus vulgaris, and Yersinia enterocolitica and to the plasmid-mediated extended-spectrum beta-lactamases MEN-1 and Toho-1. By colony hybridization with 86 strains susceptible and resistant to aztreonam, isolated in six countries, K. oxytoca beta-lactamase genes hybridized with either a specific blaOXY-1 DNA probe (668 bp) or a blaOXY-2 DNA probe (723 bp). Thus, beta-lactamase genes could be divided into two groups: blaOXY-1 (47% of the strains) and blaOXY-2 (53% of the strains). A study of isoelectric points confirmed the great variability reported in the literature. However, the two beta-lactamase groups were each represented by four different pIs: for OXY-2, 5.2, 5.7, 6.4, and 6.8, with the 5.2 form representing 59% of all OXY-2 enzymes, and for OXY-1, 7.1, 7.5, 8.2, and 8.8, with the 7.5 form representing 88% of all OXY-1 enzymes.
Collapse
Affiliation(s)
- B Fournier
- Laboratoire de Microbiologie, Université Paris VII, France
| | | | | | | |
Collapse
|
28
|
Knox JR. Extended-spectrum and inhibitor-resistant TEM-type beta-lactamases: mutations, specificity, and three-dimensional structure. Antimicrob Agents Chemother 1995; 39:2593-601. [PMID: 8592985 PMCID: PMC162995 DOI: 10.1128/aac.39.12.2593] [Citation(s) in RCA: 244] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Affiliation(s)
- J R Knox
- Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3125, USA.
| |
Collapse
|