1887

Abstract

The effects of imipenem and meropenem on the transcriptional expression of resistance-related genes , and in were studied by quantitative real-time PCR. Four strains were examined: the type strain PT5 (PAO1), its derivatives M7 and PT149, and a clinical isolate, PaKT3. The derivative M7 is a mutant, overexpressing the MexAB–OprM pump, and the derivative PT149 is a C-type mutant, overexpressing the MexEF–OprN pump while it is down-regulated for the OprD protein. After 18 h incubation in broth, the cultures were divided into three portions. Two were supplemented with antibiotics and the other was left antibiotic-free as the control. After a further 45 min incubation, total RNA was isolated from the strains by guanidine denaturation and acid-phenol/chloroform extraction. DNA-free total RNAs were immediately reverse-transcribed by MMuLV reverse transcriptase. Concentrations of mRNAs obtained by quantitative PCR were expressed relative to uninduced portions of the strains. The results showed that was relatively stable against carbapenem antibiotics. was induced significantly by imipenem in only one strain and was induced by imipenem in most of the strains. The responses at the mRNA level found here were unexpected and suggested a chaotic, unpredictable regulatory mechanism.

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2004-09-01
2019-11-14
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