Identification of SmrA, a novel efflux pump involved in fluoroquinolone resistance in Streptococcus suis

Abstract number: P1237

Escudero J.A., San Millán A., Hidalgo L., Gutierrez B., Nieto S., Domínguez L., De la Campa A.G., González-Zorn B.

Objectives:Streptococcus suis is a world-wide distributed pathogen with increasing prevalence in humans. It has recently been reported as the cause of high mortality outbreaks in Southeast Asia among the population in close contact with infected pigs or contaminated food.

During the last years rising fluoroquinolone resistance among Spanish isolates collected in our laboratory has been observed. We have recently described the influence in this phenotype of mutations in gyrA and parC, the genes encoding the drug's targets (Escudero et al. AAC 2007 51:777–82). Interestingly, the MIC of some strains was reduced in presence of reserpine pointing to the coexistance of a drug efflux phenomenon.

Methods: Strains identification was PCR based. MICs were carried out following CLSI guidelines. PFGE was performed using ApaI endonuclease. Sequencing of PCR products was performed by Secugen S.L. 4Peaks, CLC workbench, DNA Strider and Phyre ( were used for sequence analysis and protein modeling.

Results:S. suis available genomes were scanned for the presence of putative efflux pumps. A gene encoding a 401 aminoacid protein sharing 58% homology with PmrA, an efflux pump related to fluoroquinolone resistance in S. pneumoniae, was identified and named SmrA (suis multidrug resistance). Protein modeling of SmrA, revealed 12 transmembrane segments and elicited to assign this putative pump to the Major Facilitator Superfamily (MFS). Complete nucleotide sequence of smrA including its promoter region was determined from five fluoroquinolone susceptible clinical isolates, three high level resistant and two intermediate level resistant strains. PFGE of all strains revealed no genetic link between all isolates. Sequencing of these regions revealed the presence of mutations leading to a critical aminoacid substitution in position 107 (V/T107A) in all five resistant clinical isolates. Furthermore the three high level resistant isolates bore mutations in the putative -10 box, indicating that, as for other MFS members, protein structure together with expression levels are involved in SmrA mediated fluoroquinolone resistance in S. suis.

Conclusion: SmrA is a novel member of the Major Facilitator Superfamily and plays a role in fluoroquinolone resistance in clinical S. suis isolates. Acquisition of this efflux phenotype seems to be a stepwise phenomenon involving mutations in the promoter region as well as in the structural gene of SmrA.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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