Efflux pump Lde is associated with fluoroquinolone resistance in Listeria monocytogenes

Abstract

Five Listeria monocytogenes isolates (CLIP 21369, CLIP 73298, CLIP 74811, CLIP 75679, and CLIP 79372) were found to be resistant to fluoroquinolones during the screening for antibiotic resistance of 488 L. monocytogenes isolates from human cases of listeriosis in France. On the basis of a fourfold or greater decrease in the ciprofloxacin MIC in the presence of reserpine, fluoroquinolone resistance was attributed to active efflux of the drugs. The lde gene (Listeria drug efflux; formerly lmo2741) encodes a 12-transmembrane-segment putative efflux pump belonging to the major facilitator superfamily of secondary transporters that displayed 44% identity with PmrA from Streptococcus pneumoniae. Insertional inactivation of the lde gene in CLIP 21369 indicated that the corresponding protein was responsible for fluoroquinolone resistance and was involved in the level of susceptibility to dyes such as ethidium bromide and acridine orange.

FIG. 1.

Alignment of the deduced sequences of 12-TMS MFS proteins from gram-positive bacteria. Bmr, from B. subtilis (GenBank accession number L25604); EmeA, from E. faecalis (10); NorA, from S. aureus (GenBank accession number AB019536); PmrA, from S. pneumoniae (GenBank accession number AJ007367); Lde, from L. monocytogenes EGDe (this study and GenBank accession number AL591984). Identical amino acids are indicated by boldface letters on a black background, and conservative substitutions are indicated by letters on a grey background. The horizontal lines above the alignment indicate the locations of the 12 TMSs (1 to 12). Highly conserved motifs (motifs A, B, C, D2, and G) are displayed below the alignment.