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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A gene bank from a clinical isolate of Clostridium difficile expressing high chloramphenicol acetyltransferase activity was constructed by cloning Sau3A-cleaved clostridial DNA fragments into the plasmid vector pUC13. Among 1,020 clones tested, 11 were resistant to chloramphenicol; 1 of these, with an insert size of 1.9 kilobases (pPPM9), was studied further. The clone pPPM9 was mapped using a variety of restriction enzymes, and a 0.27-kilobase EcoRV-TaqI restriction fragment was shown to be within the chloramphenicol resistance (Cmr) gene by using transposon (Tn1000) mutagenesis. The 0.27-kilobase fragment and the 1.9-kilobase insert were radiolabeled and used as DNA probes in hybridization studies. Southern blot analysis with the gene probes against chromosomal DNA from Cmr strains of C. difficile obtained from five distinct geographical locations revealed that at least two copies of the same chloramphenicol acetyltransferase gene were present for each strain. Hybridization of the gene probes against Cmr strains of Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella edwardsii, Escherichia coli, and to four other clostridial species revealed no homology even under conditions of low stringency.
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PMID:Molecular cloning and genetic analysis of a chloramphenicol acetyltransferase determinant from Clostridium difficile. 284 49

For large scale isolation of chloramphenicol acetyltransferase (CAT), five soil bacteria (Alkaligens faecalis cc; Escherichia coli c-18; Escherichia coli c-22; Escherichia coli c-24 and Klebsiella pneumoniae c-38) resistant to chloramphenicol (Cm) were tested with surface active agents such as sodium dodecyl sulphate (SDS), triton x-100, tween-80 and sodium deoxycholate (SDC). CAT leakage was satisfactory with SDS and SDC. Since SDS forms a covalent complex with certain proteins, extraction of CAT was performed with SDC in the present study. The enzyme was partially purified by a gel filtration procedure. The stability test showed that the CAT enzymes isolated from E. coli c-22 and K. pneumoniae c-38, were fairly stable even at room temperature. The CAT isolated in this way may be useful for sterility testing of Cm containing products.
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PMID:Isolation of chloramphenicol acetyltransferase from soil bacteria for sterility testing of products containing chloramphenicol. 385 34

The mechanisms of resistance encountered in bacteria causing infection in the patient at risk for infection are diverse. Most resistance currently seen is the result of plasmid transfer rather than mutational events. However, extensive use of antimicrobial agents in the hospital has caused the selection of organisms resistant to many agents by virtue of chromosomally mediated mechanisms. Staphylococcus aureus resistant to beta-lactams due to altered penicillin-binding proteins has become a problem in certain patients such as narcotic addicts and chronic care facility patients exposed to many beta-lactam antibiotics. S. epidermidis has also proved to be a problem in patients with indwelling foreign devices, and altered penicillin-binding proteins also make these organisms resistant to available penicillins and cephalosporins. Streptococcus fecalis has become increasingly resistant to aminoglycosides, erythromycin, and tetracyclines due to plasmid-mediated enzymes. Hemophilus influenzae resistant to both penicillins and chloramphenicol by virtue of beta-lactamases and chloramphenicol transacetylase has been encountered. Beta-lactamase-mediated resistance of Enterobacteriaceae, Escherichia coli, and Klebsiella pneumoniae to beta-lactam antibiotics has increased, and resistance of Serratia marcescens and Pseudomonas aeruginosa to aminoglycosides and penicillins is a widespread phenomenon. Mechanisms to reduce resistance will include not only careful attention to hygienic practices but also more appropriate use of antibiotics selecting the proper agent depending on the type of patient and environment in which the infection develops.
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PMID:Current mechanisms of resistance to antimicrobial agents in microorganisms causing infection in the patient at risk for infection. 637 59

After screening 107 soil samples collected from different spots around Calcutta, 579 chloramphenicol resistant colonies were isolated. Out of these only 58 colonies could inactivate chloramphenicol in detectable amounts. By noting the production of inactivating factor, 5 high yielding strains were further characterized to species level. Three of them were Escherichia coli strains, the two others were Alcaligenes faecalis and Klebsiella pneumoniae strains. All strains inactivated chloramphenicol by acetylation, with the production of chloramphenicol acetyltransferase. Production of this latter enzyme was not inducible. Minimum inhibitory concentrations for these 5 strains were studied against 14 antimicrobial agents. All strains were found to be resistant to most antimicrobial agents, but sensitive to polymyxin B. The strain A. faecalis was also sensitive to carbenicillin but other four strains were resistant to this antibiotic.
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PMID:Isolation of bacteria producing chloramphenicol acetyltransferase from soil and their characterization. 695 90

We evaluated the in vitro antimicrobial activity of Sch 24893, Sch 25298, and Sch 25393, three novel analogs of chloramphenicol and thiamphenicol. All of the analogs had minimal inhibitory concentrations of less than or equal to 10 micrograms/ml for 18 chloramphenicol-thiamphenicol-resistant strains of Shigella dysenteriae and 21 strains of resistant Salmonella typhi. The analogs were also more active than were chloramphenicol and thiamphenicol against chloramphenicol-resistant enteric bacteria, including six strains of Escherichia coli, seven strains of Klebsiella pneumoniae, and two strains of Enterobacter cloacae. Fifty-three strains of ampicillin-resistant Haemophilus influenzae were uniformly susceptible to chloramphenicol, thiamphenicol, and the three analogs. Sch 25298 was the most active compound tested (minimal inhibitory concentration, 0.5 microgram/ml for all strains). Four of seven chloramphenicol-thiamphenicol-resistant Haemophilus strains were susceptible to the fluorinated analogs. Of the three Haemophilus strains which were resistant to chloramphenicol, thiamphenicol, and the analogs, two contained less than 10% of the chloramphenicol acetyltransferase activity of the strains which were resistant to only chloramphenicol and thiamphenicol. We conclude that fluorinated analogs of chloramphenicol and thiamphenicol have considerable in vitro activity against a broad spectrum of chloramphenicol-thiamphenicol-resistant, gram-negative bacteria.
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PMID:In vitro antibacterial activity of fluorinated analogs of chloramphenicol and thiamphenicol. 695 62

The in vitro activity of three fluorine analogs of chloramphenicol in which the hydroxyl group at position 3 had been replaced with a fluorine was compared with that of chloramphenicol and thiamphenicol. Compound SCH 24893 was the most active agent against staphylococci and Bacteroides strains, and compound SCH 25298 was the most active against Haemophilus, Neisseria, enterococcus, and Klebsiella strains. Serratia marcescens and Pseudomonas aeruginosa strains resistant to chloramphenicol were resistant to the compounds. The agents inhibited all of the Shigella, Salmonella, Staphylococcus aureus, and enterococcus strains resistant to chloramphenicol. They inhibited most (82%) of Escherichia coli and half of the Klebsiella pneumoniae strains which were resistant to chloramphenicol. Isolates in which resistance to chloramphenicol was shown to be plasmic mediated and due to chloramphenicol transacetylase were inhibited by all three agents.
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PMID:In vitro activity of chloramphenicol and thiamphenicol analogs. 744 8

A 1954-bp DNA fragment containing the blaMOX-1 gene, identified on a large resident plasmid (pRMOX-1) of Klebsiella pneumoniae NU2936, was sequenced and an open reading frame (ORF) coding for a 390-amino-acid (aa) MOX-1 was found. The total deduced aa sequence of MOX-1 shared considerable homology with that of AmpC-type class C beta-lactamases of Gram- bacteria, especially of Pseudomonas aeruginosa PAO1 [51.3%; 63.8% at the nucleotide (nt) level]. However, the regulatory gene ampR and a 38-bp AmpR-binding region were not present upstream from blaMOX-1, although the expression of P. aeruginosa ampC is directly regulated by AmpR. Possible -35 and -10 regions, a Shine-Dalgarno (SD) sequence and terminators were identified which are peculiar to blaMOX-1. On the other hand, a sequence highly homologous (91.6%) to the region upstream from dhfrX in the In7 integron carried by plasmid pDGO100 was found upstream from blaMOX-1 at nt 1 to 488. No significant difference was detected between the promoter activities of blaMOX-1 in ampD- and ampD+ strains of Enterobacter cloacae, as measured by the chloramphenicol acetyltransferase (CAT) assay. These results clearly show that blaMOX-1 belongs to the group of ampC-related bla genes and that it is expressed constitutively, independently of transcriptional regulators such as AmpR, AmpG and AmpD. Homology analysis among AmpC enzymes or ampC genes implied that integration of the chromosomal ampC gene into a large resident plasmid, followed by transconjugation, was involved in the evolution of blaMOX-1.
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PMID:Characterization of a plasmid-borne and constitutively expressed blaMOX-1 gene encoding AmpC-type beta-lactamase. 811 96

The two groups of chromosomal beta-lactamases from Klebsiella oxytoca (OXY-1 and OXY-2) can be overproduced 73- to 223-fold, due to point mutations in the consensus sequences of their promoters. The different versions of promoters from blaOXY-1 and blaOXY-2 were cloned upstream of the chloramphenicol acetyltransferase (CAT) gene of pKK232-8, and their relative strengths were determined in Escherichia coli and in K. oxytoca. The three different mutations in the OXY beta-lactamase promoters resulted in a 4- to 31-fold increase in CAT activity compared to that of the wild-type promoter. The G-->T transversion in the first base of the -10 consensus sequence caused a greater increase in the promoter strength of the wild-type promoter than the two other principal mutations (a G-to-A transition of the fifth base of the -10 consensus sequence and a T-to-A transversion of the fourth base of the -35 sequence). The strength of the promoter carrying a double mutation (transition in the Pribnow box and the transversion in the -35 hexamer) was increased 15- to 61-fold in comparison to that of the wild-type promoter. A change from 17 to 16 bp between the -35 and -10 consensus sequences resulted in a ninefold decrease of the promoter strength. The expression of the blaOXY promoter in E. coli differs from that in K. oxytoca, particularly for promoters carrying strong mutations. Furthermore, the blaOXY promoter appears not to be controlled by DNA supercoiling or an upstream curved DNA, but it is dependent on the gene copy number.
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PMID:Strength and regulation of the different promoters for chromosomal beta-lactamases of Klebsiella oxytoca. 1010 90

The location and environment of the acquired blaIMP gene, which encodes the IMP-1 metallo-beta-lactamase, were investigated in a Japanese Pseudomonas aeruginosa clinical isolate (isolate 101/1477) that produced the enzyme. In this isolate, blaIMP was carried on a 36-kb plasmid, and similar to the identical alleles found in Serratia marcescens and Klebsiella pneumoniae clinical isolates, it was located on a mobile gene cassette inserted into an integron. The entire structure of this integron, named In31, was determined. In31 is a class 1 element belonging to the same group of defective transposon derivatives that originated from Tn402-like ancestors such as In0, In2, and In5. The general structure of In31 appeared to be most closely related to that of In5 from pSCH884, suggesting a recent common phylogeny for these two elements. In In31, the blaIMP cassette is the first of an array of five gene cassettes that also includes an aacA4 cassette and three original cassettes that have never been described in other integrons. The novel cassettes carry, respectively, (i) a new chloramphenicol acetyltransferase-encoding allele of the catB family, (ii) a qac allele encoding a new member of the small multidrug resistance family of proteins, and (iii) an open reading frame encoding a protein of unknown function. All the resistance genes carried on cassettes inserted in In31 were found to be functional in decreasing the in vitro susceptibilities of host strains to the corresponding antimicrobial agents.
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PMID:Structure of In31, a blaIMP-containing Pseudomonas aeruginosa integron phyletically related to In5, which carries an unusual array of gene cassettes. 1010 96

A novel expression system of Klebsiella pneumoniae was developed in order to improve 1,3-propanediol (1,3-PD) production using a K. pneumoniae-Escherichia coli shuttle vector pET28a consisting of the kanamycin-resistance gene promoter Pkan. The recombinant plasmid pETPkan-cat carrying the chloramphenicol acetyltransferase gene cat as selectable marker was constructed to test the availability of the promoter Pkan in K. pneumoniae. The results showed that the chloramphenicol acetyltransferase was apparently expressed in K. pneumoniae, and the recombinant strain had a high-level resistance to chloramphenicol, suggesting that the promoter Pkan was efficient in K. pneumoniae. Then, the expression system was applied to the expression of 1,3-PD oxidoreductase in K. pneumoniae. The enzyme was over-expressed, and the recombinant K. pneumoniae showed a nearly 3.0-fold decrease in peak level of the intermediary metabolite 3-hydroxypropionaldehyde and an increase of 16.5% in yield of 1,3-PD with respect to the wild-type strain. From these results, the first reported expression system has paved the way for improvement of 1,3-PD production and will be available and efficient for other heterologous gene expression in K. pneumoniae.
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PMID:Construction of a novel expression system in Klebsiella pneumoniae and its application for 1,3-propanediol production. 1972 70


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