Objectives: To assess the in vitro susceptibility of Francisella tularensis subsp. holarctica biovar II strains to 24 antimicrobial agents.
Methods: Thirty-nine F. tularensis strains isolated from humans in the Central Anatolia region of Turkey were examined. Each isolate was identified by conventional and molecular techniques. MICs of aminoglycosides, tetracyclines, fluoroquinolones, macrolides, penicillins, cephalosporins, imipenem, clindamycin, linezolid, chloramphenicol and rifampicin were determined using the Etest method on glucose/cysteine blood agar plates. Interpretation of results was made according to CLSI clinical breakpoints.
Results: All strains were susceptible to aminoglycosides, tetracyclines, chloramphenicol, rifampicin and three fluoroquinolones. In contrast, resistance to penicillins, cephalosporins, carbapenems, macrolides and clindamycin was observed for all isolates. Fluoroquinolones had the lowest MIC(50) and MIC(90).
Conclusions: All strains were susceptible to the antibiotics traditionally used to treat tularaemia, such as streptomycin (MIC(90) 1.5 mg/L), gentamicin (MIC(90) 0.25 mg/L), tetracycline (MIC(90) 0.38 mg/L) and chloramphenicol (MIC(90) 0.25 mg/L). Since fluoroquinolones showed the lowest MIC values, and have important advantages over aminoglycosides, including ease of oral administration and lower toxicities, quinolones have the potential for being effective first-line therapy for tularaemia.