To determine the drug-susceptibility profile of MTBc isolates, the proportion method is the most commonly applied (Rigouts & Cogneau, 2021).
It establishes the proportion of bacilli growing on culture-containing medium as compared to drugfree slants, considering an isolate as clinically resistant if >1% of the bacterial population resists the drug. To this end, an appropriate bacterial suspension (e.g., 10−2 or 10−1 dilution MacFarland #1) of the isolated culture is inoculated on the drug-containing slants, while a 1:100 dilution of the same suspension is inoculated on ad drug-free control.
Requirements for the analyte: Viable pure mycobacterial culture isolates on solid or in liquid medium. Upon arrival we will subculture the MTBc on Löwenstein-Jensen (LJ) medium or in liquid MGIT medium to initiate the desired testing:
- proportion method
- on solid medium (LJ and/or Middlebrook 7H11 agar medium)
- in liquid medium (MGIT960)
- determination of the minimal inhibitory concentration (MIC)
- on solid medium (LJ and/or Middlebrook 7H11 agar medium)
- in liquid medium (MGIT960)
- using the microdilution broth method (EUCAST standard) (ref)
Expected turn around time: Solid medium testing may take up to 3 months after arrival, while liquid medium testing may be available in 2 months. In case > 10 strains need to be tested, this may however take more time.
References: Rigouts & Cogneau, 2021 eBook ISBN9781003099277