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Lee J, Kim YK, Min DH. A New Assay for Endonuclease/Methyltransferase Activities Based on Graphene Oxide. Anal Chem 2011; 83:8906-12. [DOI: 10.1021/ac201298r] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Jieon Lee
- Department of Chemistry, KAIST, Daejeon, 305-701, Republic of Korea
| | - Young-Kwan Kim
- Department of Chemistry, KAIST, Daejeon, 305-701, Republic of Korea
| | - Dal-Hee Min
- Department of Chemistry, Seoul National University, Seoul, 151-747, Republic of Korea
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Abstract
This review focuses on the era of antibiosis that led to a better understanding of bacterial morphology, in particular the cell wall component peptidoglycan. This is an effort to take readers on a tour de force from the concept of antibiosis, to the serendipity of antibiotics, evolution of beta-lactam development, and the molecular biology of antibiotic resistance. These areas of research have culminated in a deeper understanding of microbiology, particularly in the area of bacterial cell wall synthesis and recycling. In spite of this knowledge, which has enabled design of new even more effective therapeutics to combat bacterial infection and has provided new research tools, antibiotic resistance remains a worldwide health care problem.
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Affiliation(s)
- Kok-Fai Kong
- Department of Biological Sciences, Florida International University, Miami, FL, USA
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Petrella S, Renard M, Ziental-Gelus N, Clermont D, Jarlier V, Sougakoff W. Characterization of the chromosomal class A β-lactamase CKO fromCitrobacter koseri. FEMS Microbiol Lett 2006; 254:285-92. [PMID: 16445758 DOI: 10.1111/j.1574-6968.2005.00028.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The gene bla(CKO) encoding the chromosomal class A beta-lactamase of Citrobacter koseri was cloned and sequenced. CKO was found to display only 41% identity with SED-1 from Citrobacter sedlakii and 36% with CdiA from Citrobacter amalonaticus (formerly Citrobacter diversus). No transcriptional regulator was found upstream from bla(CKO). Silent and missense mutations were detected in four bla(CKO) genes amplified from different C. koseri clinical isolates, but the CKO variants displayed identical biochemical behaviours. A bla(CKO)-specific polymerase chain reaction confirmed that bla(CKO) is present only in C. koseri and therefore represents an interesting tool with which to differentiate C. koseri from the other Citrobacter spp.
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Affiliation(s)
- Stephanie Petrella
- Laboratoire de Recherche Moléculaire sur les Antibiotiques, Faculté de médecine Pitié-Salpêtrière, Université Pierre et Marie Curie, Paris, France
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Petrella S, Clermont D, Casin I, Jarlier V, Sougakoff W. Novel class A beta-lactamase Sed-1 from Citrobacter sedlakii: genetic diversity of beta-lactamases within the Citrobacter genus. Antimicrob Agents Chemother 2001; 45:2287-98. [PMID: 11451687 PMCID: PMC90644 DOI: 10.1128/aac.45.8.2287-2298.2001] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Citrobacter sedlakii 2596, a clinical strain resistant to aminopenicillins, carboxypenicillins, and early cephalosporins such as cephalothin, but remaining susceptible to acylureidopenicillins, carbapenems, and later cephalosporins such as cefotaxime, was isolated from the bile of a patient treated with beta-lactam and quinolone antibiotics. The isolate produced an inducible class A beta-lactamase of pI 8.6, named Sed-1, which was purified. Characterized by a molecular mass of 30 kDa, Sed-1 preferentially hydrolyzed benzylpenicillin, cephalothin, and cloxacillin. The corresponding gene, bla(Sed-1), was cloned and sequenced. Its deduced amino acid sequence shared more than 60% identity with the chromosome-encoded beta-lactamases from Citrobacter koseri (formerly C. diversus) (84%), Klebsiella oxytoca (74%), Serratia fonticola (67%), and Proteus vulgaris (63%) and 71% identity with the plasmid-mediated enzyme MEN-1. A gene coding for a LysR transcriptional regulator was found upstream from bla(Sed-1). This regulator, named SedR, displayed 90% identity with the AmpR sequence of the chromosomal beta-lactamase from C. koseri and 63 and 50% identity with the AmpR sequences of P. vulgaris and Enterobacter cloacae, respectively. By using DNA-DNA hybridization, a bla(Sed-1)-like gene was identified in two reference strains, C. sedlakii (CIP-105037) and Citrobacter rodentium (CIP-104675), but not in the 18 strains of C. koseri studied. Two DNA fragments were amplified and sequenced from the reference strains of C. sedlakii CIP-105037 and C. rodentium CIP-104675 using two primers specific for bla(Sed-1). They shared 98 and 80% identity with bla(Sed-1), respectively, confirming the diversity of the chromosomally encoded class A beta-lactamases found in Citrobacter.
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Affiliation(s)
- S Petrella
- Laboratoire de Recherche Moléculaire sur les Antibiotiques, Faculté de Médecine Pitié-Salpêtrière, Université Pierre et Marie Curie, Paris, France
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Bush K, Jacoby GA, Medeiros AA. A functional classification scheme for beta-lactamases and its correlation with molecular structure. Antimicrob Agents Chemother 1995; 39:1211-33. [PMID: 7574506 PMCID: PMC162717 DOI: 10.1128/aac.39.6.1211] [Citation(s) in RCA: 1553] [Impact Index Per Article: 53.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- K Bush
- American Cyanamid Company, Lederle Laboratories, Pearl River, New York 10965, USA
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Osano E, Arakawa Y, Wacharotayankun R, Ohta M, Horii T, Ito H, Yoshimura F, Kato N. Molecular characterization of an enterobacterial metallo beta-lactamase found in a clinical isolate of Serratia marcescens that shows imipenem resistance. Antimicrob Agents Chemother 1994; 38:71-8. [PMID: 8141584 PMCID: PMC284399 DOI: 10.1128/aac.38.1.71] [Citation(s) in RCA: 312] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A clinical isolate of Serratia marcescens (TN9106) produced a metallo beta-lactamase (IMP-1) which conferred resistance to imipenem and broad-spectrum beta-lactams. The blaIMP gene providing imipenem resistance was cloned and expressed in Escherichia coli HB101. The IMP-1 was purified from E. coli HB101 that harbors pSMBNU24 carrying blaIMP, and its apparent molecular mass was calculated to be about 30 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Kinetic studies of IMP-1 against various beta-lactams revealed that this enzyme hydrolyzes not only various broad-spectrum beta-lactams but also carbapenems. However, aztreonam was relatively stable against IMP-1. Although clavulanate or cloxacillin failed to inhibit IMP-1, Hg2+, Fe2+, or Cu2+ blocked the enzyme's activity. Moreover, the presence of EDTA in the reaction buffer resulted in a decrease in the enzyme's activity. Carbapenem resistance was not transferred from S. marcescens TN9106 to E. coli CSH2 by conjugation. A hybridization study confirmed that blaIMP was encoded on the chromosome of S. marcescens TN9106. By nucleotide sequencing analysis, blaIMP was found to encode a protein of 246 amino acid residues and was shown to have considerable homology to the metallo beta-lactamase genes of Bacillus cereus, Bacteroides fragilis, and Aeromonas hydrophila. The G+C content of blaIMP was 39.4%. Four consensus amino acid residues, His-95, His-97, Cys-176, and His-215, which form putative zinc ligands, were conserved in the deduced amino acid sequence of IMP-1. By determination of the amino acid sequence at the N terminus of purified mature IMP-1, 18 amino acid residues were found to be processed from the N terminus of the premature enzyme as a signal peptide. These results clearly show that IMP-1 is an enterobacterial metallo beta-lactamase, of which the primary structure has been completely determined, that confers resistance to carbapenems and other broad-spectrum beta-lactams.
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Affiliation(s)
- E Osano
- Department of Bacteriology, Nagoya University School of Medicine, Japan
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Horii T, Arakawa Y, Ohta M, Ichiyama S, Wacharotayankun R, Kato N. Plasmid-mediated AmpC-type beta-lactamase isolated from Klebsiella pneumoniae confers resistance to broad-spectrum beta-lactams, including moxalactam. Antimicrob Agents Chemother 1993; 37:984-90. [PMID: 8517725 PMCID: PMC187871 DOI: 10.1128/aac.37.5.984] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Klebsiella pneumoniae NU2936 was isolated from a patient and was found to produce a plasmid-encoded beta-lactamase (MOX-1) which conferred resistance to broad spectrum beta-lactams, including moxalactam, flomoxef, ceftizoxime, cefotaxime, and ceftazidime. Resistance could be transferred from K. pneumoniae NU2936 to Escherichia coli CSH2 by conjugation with a transfer frequency of 5 x 10(-7). The structural gene of MOX-1 (blaMOX-1) was cloned and expressed in E. coli HB101. The MIC of moxalactam for E. coli HB101 producing MOX-1 was > 512 micrograms/ml. The apparent molecular mass and pI of this enzyme were calculated to be 38 kDa and 8.9, respectively. Hg2+ and Cu2+ failed to block enzyme activity, and the presence of EDTA in the reaction buffer did not reduce the enzyme activity. However, clavulanate and cloxacillin, serine beta-lactamase inhibitors, inhibited the enzyme activity competitively (Kis = 5.60 and 0.35 microM, respectively). The kinetic study of MOX-1 suggested that it effectively hydrolyzed broad-spectrum beta-lactams. A hybridization study confirmed that blaMOX-1 is encoded on a large resident plasmid (pRMOX1; 180 kb) of strain NU2936. By deletion analysis, the functional region was localized within a 1.2-kb region of the plasmid. By amino acid sequencing, 18 of 33 amino acid residues at the N terminus of MOX-1 were found to be identical to those of Pseudomonas aeruginosa AmpC. These findings suggest that MOX-1 is a plasmid-mediated AmpC-type beta-lactamase that provides enteric bacteria resistance to broad-spectrum beta-lactams, including moxalactam.
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Affiliation(s)
- T Horii
- Department of Bacteriology, Nagoya University School of Medicine, Japan
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Tsukamoto K, Tachibana K, Yamazaki N, Ishii Y, Ujiie K, Nishida N, Sawai T. Role of lysine-67 in the active site of class C beta-lactamase from Citrobacter freundii GN346. EUROPEAN JOURNAL OF BIOCHEMISTRY 1990; 188:15-22. [PMID: 1969344 DOI: 10.1111/j.1432-1033.1990.tb15365.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Citrobacter freundii GN346 produces a class C beta-lactamase exhibiting the substrate profile of a typical cephalosporinase. The structural and promoter regions of the cephalosporinase gene, comprising 1408 nucleotides, were completely sequenced. The amino acid sequence of the mature enzyme, comprising 361 amino acids, and its molecular mass, 39,878 Da, were determined. The active site was confirmed to be Ser-64. The amino acid sequence of the enzyme differs from that of the cephalosporinase of C. freundii OS60 by nine residues. The nucleotide sequence of the promoter region suggests a possible attenuator structure. Lys-67, one of the most conserved residues found in class A and C beta-lactamases and penicillin-binding proteins, was converted into arginine, threonine or glutamic acid through site-directed mutagenesis. The Glu-67 enzyme had lost the catalytic activity and the Thr-67 enzyme only showed a trace of activity. The Arg-67 enzyme, which retained a significant amount of the activity, was purified. The Km values of the Arg-67 enzyme for cephalothin, cephaloridine and benzylpenicillin are 13-19 times those of the wild-type enzyme; the kcat values for the three substrates are 37%, 3%, and 36% those of the wild-type enzyme, respectively.
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Affiliation(s)
- K Tsukamoto
- Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan
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Maejima T, Ohya Y, Mitsuhashi S, Inoue M. Cloning and expression of the gene(s) for chromosome-mediated beta-lactamase production of Proteus vulgaris in Escherichia coli. Plasmid 1987; 18:120-6. [PMID: 2829250 DOI: 10.1016/0147-619x(87)90039-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The gene(s) for chromosome-mediated beta-lactamase production of Proteus vulgaris GN7919 was cloned into a unique EcoRI site of pACYC184 as an insert of a 14.2-kb fragment, which was further digested into two fragments with EcoRI, 4.9 and 9.3 kb. The restriction enzyme digestion pattern of the recombinant plasmid, designated pMS182, had no similarity to those of other chromosomal beta-lactamase genes cloned from gram-negative bacteria. Plasmid pMS182 enabled host Escherichia coli ML4953 to inducibly produce beta-lactamase which was identical to that of the parent P. vulgaris in substrate profile, molecular weight, and reactivity to antiserum raised against P. vulgaris GN7919 beta-lactamase. The pMS182-harboring E. coli were highly resistant to beta-lactam antibiotics, possibly based on inducible production of beta-lactamase.
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Affiliation(s)
- T Maejima
- Episome Institute (Institute of Microbial Chemistry), Gunma, Japan
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Cloning and expression of Citrobacter freundii hydrogenase genes in Escherichia coli. Appl Microbiol Biotechnol 1986. [DOI: 10.1007/bf00294596] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Murayama SY, Yamamoto T, Suzuki I, Sawai T. Mutation of Escherichia coli capable of expressing gene(s) for beta-lactamase production of Citrobacter freundii. Antimicrob Agents Chemother 1986; 29:707-9. [PMID: 3518627 PMCID: PMC180472 DOI: 10.1128/aac.29.4.707] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
A mutation in a chromosomal gene of Escherichia coli, designated reb, acted in trans to increase the expression of the cloned beta-lactamase gene of Citrobacter freundii. The reb gene was located around 99 min. Deletion mutants in the cloned gene(s) which had lost the regulatory region for induction were also constructed.
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Jones HM, Gunsalus RP. Transcription of the Escherichia coli fumarate reductase genes (frdABCD) and their coordinate regulation by oxygen, nitrate, and fumarate. J Bacteriol 1985; 164:1100-9. [PMID: 2999070 PMCID: PMC219303 DOI: 10.1128/jb.164.3.1100-1109.1985] [Citation(s) in RCA: 73] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The fumarate reductase enzyme complex allows Escherichia coli to grow anaerobically with fumarate as a terminal electron acceptor for oxidative phosphorylation when the preferred compounds oxygen and nitrate are not available. We used the pKO promoter test vectors to identify a single promoter for the frdABCD genes which encode fumarate reductase. Expression of galactokinase from the frd promoter-galK operon fusion plasmid was repressed by oxygen and by nitrate and was induced by fumarate, indicating that frd gene expression is regulated at the transcriptional level by these terminal electron acceptors. S1 nuclease analysis, using a single-stranded DNA probe from the frd promoter region and mRNA isolated from a fumarate reductase-induced culture, revealed that the frd mRNA transcript initiates with an adenine residue 93 bases prior to the start of frdA translation. No promoters internal to the frd genes were revealed with the plasmid promoter screening system. S1 nuclease analysis revealed that the frd mRNA terminates in a uridine-rich region centered at 46 bases after the last codon of frdD. A stem and loop structure previously described as the growth rate-dependent attenuator for the linked ampC gene precedes the frd mRNA terminus. This result confirms the proposal that the stem and loop structure serves the dual role of a frd terminator anaerobically and an ampC attenuator aerobically. The four frd genes encoding the subunits of the fumarate reductase complex thus comprise an operon which is regulated at the transcriptional level in response to the cellular availability of the alternate electron acceptors oxygen, nitrate, and fumarate.
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Restriction mapping and partial characterization of β-isopropylmalate dehydrogenase gene cloned from Citrobacter freundii. J Biotechnol 1985. [DOI: 10.1016/0168-1656(85)90054-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Baumberg S, Roberts M. Anomalous expression of the E. coli lac operon in Proteus mirabilis. II. Effects of lacI and lacP mutations. MOLECULAR & GENERAL GENETICS : MGG 1984; 198:166-71. [PMID: 6441103 DOI: 10.1007/bf00328717] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The lac operon introduced into Proteus mirabilis shows two anomalies of expression: the maximal induced level is reduced by about an order of magnitude, and the basal level becomes about 100 times higher than in E. coli, as a result of which the induction ratio appears very small, around 2-5 in contrast to as much as 1000 in E. coli. It was suggested by Baumberg and Dennison (1975) that the two anomalies might be manifestations of a single effect whereby some exogenous promoters give poor expression in this host, since they could result from poor expression of the lacZYA and lacI promoters respectively. We show here that when the lacP class II promoter mutation L305 was transferred on an F-prime into P. mirabilis, its effect on lac expression was much as in E. coli. However, when Flac bearing the IQ1 up-promoter mutation was introduced into P. mirabilis, the basal level decreased by three orders of magnitude, in accord with poor expression of lacI+ being responsible for the usual low induction ratio. These results are consistent with the hypothesis of Baumberg and Dennison (1975) but do not prove it: poor expression of lacI and/or lacZYA could also result from weak translation initiation, problems of continuation of transcription or translation (e.g. due to pause sequences or differences in codon use), or diminished mRNA stability.
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Cloning and expression of Citrobacter freundii ?-isopropylmalate dehydrogenase gene in both Escherichia coli and Bacillus subtilis. Appl Microbiol Biotechnol 1984. [DOI: 10.1007/bf00270597] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Gootz TD, Jackson DB, Sherris JC. Development of resistance to cephalosporins in clinical strains of Citrobacter spp. Antimicrob Agents Chemother 1984; 25:591-5. [PMID: 6610388 PMCID: PMC185593 DOI: 10.1128/aac.25.5.591] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The predominant beta-lactam antibiogram of Citrobacter freundii resembles that of Enterobacter cloacae in demonstrating resistance to cephalothin and cefoxitin with susceptibility to the newer cephalosporins. Four representative strains of C. freundii were reversibly induced to high-level beta-lactamase production by cefoxitin, and mutants with stable, high-level production were selected with cefamandole. The mutants were resistant to several second- and third-generation cephalosporins. Comparisons of isoelectric points and substrate profiles of beta-lactamases from wild-type, induced wild-type, and mutant organisms suggested a close relationship to those from E. cloacae and indicated that C. freundii mutants, like those of E. cloacae, were derepressed for production of beta-lactamase. One primary isolate of C. freundii resembled the mutants in all characteristics. In contrast, most strains of Citrobacter diversus were susceptible to all cephalosporins, and two representative strains showed neither inducible nor mutational resistance. Cefoxitin induction to enhanced beta-lactamase production was demonstrated in a cephalothin-resistant isolate, and a derepressed mutant was selected with cefotaxime. The beta-lactamase from this C. diversus strain differed substantially in substrate profile from that of E. cloacae and C. freundii.
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Seeberg AH, Wiedemann B. Transfer of the chromosomal bla gene from Enterobacter cloacae to Escherichia coli by RP4::mini-Mu. J Bacteriol 1984; 157:89-94. [PMID: 6317658 PMCID: PMC215134 DOI: 10.1128/jb.157.1.89-94.1984] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The resistance gene for beta-lactamase-stable cephalosporins from Enterobacter cloacae was transferred to Escherichia coli by the aid of RP4::mini-Mu. The R-prime plasmids generated carried 60 to 80 kilobases (kb) of E. cloacae DNA and coded for the chromosomal E. cloacae beta-lactamase. The gene was fully expressed in the recipient. Restriction endonuclease EcoRI fragments of the R-prime plasmid pBP100 were cloned into the vector pBP328, yielding the plasmid pBP102 with a size of 14 kb. A restriction map of this plasmid was constructed. By digesting pBP102 into seven PstI fragments, ligating the fragments, and looking for the smallest plasmid generated, pBP103 was isolated. It consisted of three PstI fragments, two of them (together 4.2 kb) necessary for resistance. During the experiment (performed in a recA+ background) the largest PstI fragment had undergone a substitution of a 0.3-kb segment of pBP102 by a 0.7-kb segment in pBP103 (as deduced by heteroduplex analysis). The bla gene of resistant E. cloacae strains was dominant over the gene of susceptible organisms.
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Bergström S, Lindberg FP, Olsson O, Normark S. Comparison of the overlapping frd and ampC operons of Escherichia coli with the corresponding DNA sequences in other gram-negative bacteria. J Bacteriol 1983; 155:1297-305. [PMID: 6350266 PMCID: PMC217828 DOI: 10.1128/jb.155.3.1297-1305.1983] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Specific DNA probes from Escherichia coli K-12 were used to analyze the sequence divergence of the frd and ampC operons in various species of gram-negative bacteria. These operons code for the fumarate reductase complex and the chromosomal beta-lactamase, respectively. We demonstrate that the two operons show the same general pattern of divergence, although the frd operon is considerably more conserved than is the ampC operon. The major exception is Salmonella typhimurium LT2, which shows a strong homology to the E. coli frd probe but none to the E. coli ampC probe. The operons from Citrobacter freundii and Shigella sonnei were cloned and characterized by physical mapping, Southern hybridization, and protein synthesis in minicells. In S. sonnei, as in E. coli K-12, the frd and ampC operons overlap (T. Grundström and B. Jaurin, Proc. Natl. Acad. Sci. U.S.A. 79:1111-1115, 1982). Only minor discrepancies between the two operons were found over the entire frd-ampC region. In C. freundii, the ampC and frd operons do not overlap, being separated by about 1,100 base pairs. Presumably the inducible property of the C. freundii chromosomal beta-lactamase is encoded by this 1,100-base-pair DNA segment.
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