In vitro susceptibility of Burkholderia cepacia complex isolates: Comparison of disk diffusion, Etest®, agar dilution, and broth microdilution methods

Broth microdilution, agar dilution, Etest® and disk diffusion techniques were compared to evaluate the susceptibility profile of 82 Bcc clinical isolates against six antimicrobials as recommended by CLSI. Broth microdilution was considered the “gold standard” method. The regression analysis was applied to determine the essential (EA) and categorical (CA) agreement rates. STX (MIC50, 1 mg/L) was the most potent antimicrobial tested against Bcc isolates. The worst in vitro activity was observed for chloramphenicol (MIC50, 16 mg/L) and ticarcillin-clavulanic acid (MIC50, >256 mg/L). The EA among broth microdilution and agar dilution results was good for the majority of antimicrobial tested. When comparing broth microdilution and Etest®, ceftazidime, SXT and chloramphenicol exhibited EA rates below 90%. SXT showed an excellent CA (100%) when dilution methodologies were compared. However, a low CA rate was found for this agent between dilution and disk diffusion methodologies resulting in unacceptable very major and minor error rates.