Objectives: A new pentapeptide repeat (PRP) protein, named SmaQnr, from the clinically relevant species Serratia marcescens, which decreased susceptibility to quinolones when expressed in Escherichia coli, is reported herein.
Methods: In silico analysis revealed the presence of a gene encoding a Qnr-like protein that shares 80% amino acid identity with QnrB1 in the S. marcescens strain Db11. Fragments carrying the coding region and the upstream non-coding sequences of eight clinical isolates were cloned and expressed in E. coli. MIC values of quinolones were determined. RT-PCR was used to study expression of these genes in their natural host. Southern hybridization was used to explore the presence of the gene in the genus Serratia.
Results: Recombinant plasmids encoding SmaQnr reduced susceptibility to fluoroquinolones and nalidixic acid in both E. coli ATCC 25922 and DH10B. Sequences upstream of these genes contain a LexA box. Conventional RT-PCR showed transcription of the analysed Smaqnr genes in their natural hosts. Southern blot analysis suggests the presence of similar genes in several species of the genus Serratia.
Conclusions: SmaQnr conferred a reduced susceptibility phenotype against fluoroquinolones in E. coli. These data provide evidence of its possible role in quinolone resistance in S. marcescens. This Gram-negative species may constitute a reservoir for qnr-like quinolone resistance genes.