Fluoroquinolone Efflux in Streptococcus suis Is Mediated by SatAB and Not by SmrA.

Abstract

Streptococcus suis is an emerging zoonotic pathogen. However, with the lack of an effective vaccine, antibiotics remain the main tool to fight against infections caused by this pathogen. We have previously observed a reserpine-sensitive fluoroquinolone-efflux phenotype in this species. Here, SatAB and SmrA, two pumps belonging to the ATP Binding Cassette and the Major Facilitator Superfamily respectively, have been analyzed in the fluoroquinolone-resistant clinical isolate BB1013. Genes encoding these pumps were overexpressed either constitutively or in the presence of ciprofloxacin in this strain. These genes could not be cloned onto plasmids in E. coli despite strong expression repression. Finally, site directed insertion of smrA and satAB in the amy locus of Bacillus subtilis chromosome using ligated PCR amplicons allowed for the functional expression and study of both pumps. Results showed that SatAB is a narrow spectrum fluoroquinolone exporter (norfloxacin and ciprofloxacin), susceptible to reserpine, whereas SmrA was not involved in fluoroquinolone extrusion. Chromosomal integration in Bacillus is a novel method for studying efflux pumps from Gram-positive bacteria, which enabled us to demonstrate the implication of SatAB, and not of SmrA, in fluoroquinolone efflux in S. suis.

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