Heterogeneity of susceptibility to fluoroquinolones in Bartonella isolates from Australia reveals a natural mutation in gyrA.
OBJECTIVE
Bartonella sp. are intracellular bacteria associated with an increasing number of clinical manifestations but with few published data on in vitro susceptibility testing of antibiotics. Our objective was to evaluate in vitro antibiotic susceptibilities of 20 new Bartonella isolates from animals in Australia.


METHODS
MICs were determined using Etest assay on Columbia agar supplemented with 5% horse blood. The presence of mutations in the quinolone-resistance-determining region (QRDR) of gyrA was searched for after PCR amplification and DNA sequencing using specific oligonucleotide primers.


RESULTS
Bartonella isolates from Australia were susceptible to rifampicin, tetracyclines, beta-lactam and macrolide compounds but were resistant to vancomycin. We found heterogeneity of susceptibility for fluoroquinolones with ciprofloxacin being more effective (MICs from 0.06 to 0.5 mg/L) than ofloxacin (MICs from 0.5 to 4 mg/L). This heterogeneity was linked to a natural mutation Ser-83-->Ala (Escherichia coli numbering) in the QRDR. Surprisingly, this mutation was also present in the QRDR of Bartonella henselae, Bartonella quintana and Bartonella bacilliformis.


CONCLUSIONS
Etest is a sensitive and reliable assay for evaluation of antibiotic susceptibility in the genus Bartonella. The higher sensitivity of this method allowed us to detect heterogeneity of susceptibility among fluoroquinolones that was associated with natural mutation in the QRDR of the DNA gyrase. Because a high level of resistance to fluoroquinolones due to a second mutation may be obtained easily in vitro, we believe that fluoroquinolone compounds should be avoided for the treatment of any Bartonella-related diseases.
Angelakis
Emmanouil
E
Unité des Rickettsies, CNRS UMR 6020, IFR 48, Faculté de Médecine et de Pharmacie Université de la Méditerranée, 27 Bd Jean Moulin, 13385 Marseille Cedex 05, France.
Biswas
Silpak
S
Taylor
Carmel
C
Raoult
Didier
D
Rolain
Jean-Marc
JM
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D000835:Animals, Wild / Q000382:microbiology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001315:Australia; D001474:Bartonella Infections / Q000382:microbiology; D045503:Bartonella bacilliformis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D018416:Bartonella henselae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D018413:Bartonella quintana / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D027081:DNA Gyrase / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D027081:DNA Gyrase