Smaqnr, a new chromosome-encoded quinolone resistance determinant in Serratia marcescens.
OBJECTIVE
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.
Velasco
C
C
Department of Microbiology, University of Seville, Seville, Spain. cvelasco@us.es
Rodríguez-Martínez
J M
JM
Briales
A
A
Díaz de Alba
P
P
Calvo
J
J
Pascual
A
A
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015139:Blotting, Southern; D003001:Cloning, Molecular; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D015363:Quinolones / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012706:Serratia marcescens / Q000187:drug effects* / Q000235:genetics*
D000900:Anti-Bacterial Agents; D015363:Quinolones