Relative Strengths and Regulation of Different Promoter-Associated Sequences for Various blaSHV Genes and Their Relationships to β-Lactam Resistance

Abstract

<b><i>Aims:</i></b> This work investigated the relative strengths of different <i>bla</i>_SHV promoter-associated sequences and their regulation function in <i>bla</i>_SHV expression and β-lactam resistance. <b><i>Methods:</i></b> Recombinant plasmids with the promoter-associated sequences (P-W, P-S, P-IS, and P-WPD), <i>tac</i> promoter, and combined fragments of promoter and <i>bla</i>_SHV were separately constructed and transformed into <i>Escherichia coli</i> DH5α. The relative strengths of the promoters indicated by the intensities of green fluorescent protein and the mRNA expression levels of <i>bla</i>_SHV were compared. The minimum inhibitory concentration and extended spectrum β-lactamase phenotypes were evaluated. <b><i>Results:</i></b> The relative strengths were ranked as P-<i>tac</i> > P-WPD > P-IS > P-S > P-W. The mRNA expression and β-lactam resistance levels of the different promoter-associated sequence groups were generally consistent with the strength rank, but the extent of <i>gfp</i> and <i>bla</i>_SHV mRNA levels varied significantly in each group. The β-lactam resistance levels were inconsistent with the strength rank in certain <i>bla</i>_SHV groups. In relation to the different promoter-associated sequences,<i> bla</i>_SHV-ESBLs displayed significantly different change modes of β-lactam resistance compared with <i>bla</i>_{SHV-non-ESBLs}. <b><i>Conclusion:</i></b> The mRNA expression and β-lactam resistance of the <i>bla</i>_SHV showed consistencies and inconsistencies with the strengths of the promoter-associated sequences. The mechanisms accounting for these discrepancies need further investigation.