https://scholars.lib.ntu.edu.tw/handle/123456789/188286
標題: | High-Level Expression of Ampc Beta-Lactamase Due to Insertion of Nucleotides between-10 and-35 Promoter Sequences in Escherichia Coli Clinical Isolates: Cases Not Responsive to Extended-Spectrum-Cephalosporin Treatment | 作者: | CHANG, SHAN-CHWEN | 關鍵字: | FIELD GEL-ELECTROPHORESIS;MOLECULAR-BASIS;RESISTANCE;HYPERPRODUCTION;IDENTIFICATION;MUTATIONS | 公開日期: | 2003 | 卷: | v.47 | 期: | n.7 | 起(迄)頁: | 2138-2144 | 來源出版物: | ANTIMICROBIAL AGENTS AND CHEMOTHERAPY | 摘要: | Two Escherichia coli isolates were recovered from the blood of two cancer patients and were demonstrated to produce high levels of the AmpC beta- lactamase with isoelectric points of >9.0. The hypertranscription of ampC RNA was observed by Northern blot hybridization in both isolates. One isolate ( isolate EC44) had a point mutation (G-->A at position -28) and insertion of thymidine between positions -20 and -19 of the ampC promoter gene (GenBank accession no. AE000487). The single nucleotide insertion of T between positions -19 and- 20 created an optimal distance (17 bp) in the Pribnow box for ampC hyperproduction. The other isolate (isolate EC38) had two point mutations (G-->A at position -28 and C-->T at position +58) and a 2-base (GT) insertion between positions- 14 and -15. Although the insertion of GT between positions- 14 and -15 may create a new promoter next to the original promoter, cloning of the ampC region with truncated nucleotides of the original -35 region of EC38 failed to verify the hypothesis that a new promoter would be created by such a nucleotide insertion. Instead, multiple start sites for ampC transcription at -1, +1, +2, and +3 were observed in an S1 nuclease protection assay. These results suggest that the RNA polymerase is flexible in the selection of a start site in ampC hypertranscription. In conclusion, nucleotide insertions between the -35 and -10 ampC promoter sequences was the mechanism for the hyperproduction of AmpC P-lactamase and resistance to oxyimino-cephalosporins. The failure of the two patients to respond to treatment with oxyimino-cephalosporins highlights the important role of such a resistance mechanism in the clinical setting. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/95234 |
顯示於: | 醫學系 |
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