title: Deleterious effect of ciprofloxacin on Rickettsia conorii-infected cells is linked to toxin-antitoxin module up-regulation.
abstract: OBJECTIVE
  To confirm and better understand the deleterious effect of fluoroquinolones reported during Rickettsia conorii infection in humans.
  
  
  METHODS
  We used a new plaque assay to test the effect of ciprofloxacin on cells infected by R. conorii. Controls were mock-treated infected cells and infected cells treated with doxycycline. We used real-time quantitative RT-PCR to quantify vapC and vapB transcripts in cells infected by R. conorii treated with ciprofloxacin or mock treated.
  
  
  RESULTS
  By plaque assay, at baseline (0 h) there is no difference in lytic area between cells treated with ciprofloxacin (whatever concentration used) and controls. Ciprofloxacin at 0.5 and 50 mg/L induced a significant increase in lytic areas compared with the control at 2 h, 4 h, 6 h (P<0.0001) and 24 h (P<0.0001 and P=0.035, respectively) when not induced with doxycycline. By real-time quantitative RT-PCR, ciprofloxacin was found to cause an up-regulation of toxin-antitoxin (TA) module transcription. Indeed, the mRNA levels of vapC and vapB were significantly increased at 2 h and 4 h in cells treated with 50 mg/L ciprofloxacin (not with 0.5 mg/L ciprofloxacin) compared with control levels (fold change >2.9).
  
  
  CONCLUSIONS
  These in vitro findings correlated with our previous clinical findings: fluoroquinolones have a deleterious effect during R. conorii infection, not found with doxycycline. We speculate that the toxic effect of fluoroquinolones on R. conorii-infected cells is mediated by the overexpression of TA, possibly followed by their release into the host cytoplasm as described in Rickettsia felis.
authors.affiliation: URMITE UMR 6236, CNRS-IRD, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille cedex 05,  France.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Botelho-Nevers
authors.forename: Sophie
authors.initials: S
authors.lastname: Edouard
authors.forename: Quentin
authors.initials: Q
authors.lastname: Leroy
authors.forename: Didier
authors.initials: D
authors.lastname: Raoult
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis; D001427:Bacterial Toxins / Q000096:biosynthesis*; D001431:Bacteriological Techniques; D001907:Boutonneuse Fever / Q000382:microbiology*; D018929:Cell Culture Techniques; D002939:Ciprofloxacin / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D015870:Gene Expression / Q000187:drug effects*; D020869:Gene Expression Profiling; D006801:Humans; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D060888:Real-Time Polymerase Chain Reaction; D020114:Rickettsia conorii / Q000187:drug effects* / Q000302:isolation & purification / Q000472:pathogenicity*; D041161:Rickettsia felis; D013752:Tetracycline / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; C077517:VapB protein, Bacteria; D002939:Ciprofloxacin; D013752:Tetracycline