The Etest for antimicrobial susceptibility testing of Bartonella henselae

The in-vitro susceptibility of 10 isolates of Bartonella henselae was assessed using the Etest. The organisms, one reference human strain and nine feline isolates, were grown on chocolate agar and the Etests read at days 5, 8 and 11. Six antibiotics, erythromycin, azithromycin, doxycycline, ciprofloxacin, rifampicin and vancomycin were evaluated. The results correlated well with published results using agar dilution. The results confirmed the high in-vitro susceptibility of B. henselae to erythromycin, azithromycin, doxycycline and rifampicin and to a lesser extent ciprofloxacin. The majority of isolates were resistant to vancomycin. Although in-vitro results of B. henselae susceptibility testing may not necessarily correlate with clinical response, the Etest may be a simpler way for laboratories to monitor for the development of resistance particularly in the setting of relapsing infection.