Veterinary session

Francisella tularensis is the etiological agent of tularemia, a life-threatening zoonotic disease and a potential biological warfare agent. The number of the reported human cases ranged between 20 and 143 a year in Hungary in the last decade. In most cases, tick bite and close contact with European brown hares (Lepus europaeus) or rodents were found in the anamnesis. Infection in humans can be treated with antibiotics.

The aim of this study was to determine the in vitro susceptibility to 11 antibiotics of F. tularensis subsp. holarctica strains from different areas of Hungary.

F. tularensis subsp. holarctica strains were isolated from tissue samples on a modified Francis agar (chocolate agar plate containing 1% glucose and 0.1% cysteine) after a mouse passage. The isolated strains were identified by polymerase chain reaction. The antibiotic susceptibility profile of the isolates were examined with commercially available minimum inhibitory concentration (MIC) test strips on modified Francis agar plates and values were interpreted according to the Clinical and Laboratory Standards Institute breakpoints.

Twenty-nine F. tularensis subsp. holarctica strains isolated between 2003 and 2010 from free ranging European brown hares and a captive patas monkey (Erythrocebus patas) were collected from different parts of Hungary. The strains were susceptible to aminoglycosides (MIC90 value of streptomycin: 6.0 mg/l; gentamicin: 0.75 mg/l), tetracyclines (MIC90 value of tetracycline: 0.5 mg/l; doxycycline: 1.0), chloramphenicol (MIC90: 1.5 mg/l), and to fluoroquinolones (MIC90 value of ciprofloxacin: 0.047 mg/l; levofloxacin: 0.023 mg/l), i.e. antibiotics commonly used in the human therapy. Tigecycline (MIC90: 0.19 mg/l) and rifampicin (MIC90: 1.0 mg/l) were also active against F. tularensis subsp. holarctica strains, while resistance to erythromycin (MIC90: 256 mg/l<) and linezolid (MIC90: 32 mg/l) was observed in all isolates.

The promising results of in vitro susceptibility to levofloxacin and tigecycline may encourage further studies aimed at the application of these antibiotics in the therapy of tularemia.