Revisiting problems and solutions to decrease Mycobacterium tuberculosis pyrazinamide false resistance when using the Bactec MGIT 960 system

Ann Ist Super Sanita. 2019 Jan-Mar;55(1):51-54. doi: 10.4415/ANN_19_01_09.

Abstract

Pyrazinamide (PZA) is a first-line key drug used in combination with other agents for the treatment of tuberculosis (TB). Phenotypic and molecular assays for testing susceptibility of Mycobacterium tuberculosis (Mtb) to PZA have been developed, with the assay in liquid medium at acidic pH in the Bactec MGIT 960 (M960) system being routinely used in the mycobacteriology laboratories. However, false resistance to PZA by this method was reported to occur by several investigators, mostly due to high Mtb inoculum, which may impair drug activity by increasing the pH of the medium. In this study, a revision of the literature on the issue of false resistance in the M960 PZA assay was performed. In the reports examined, all improvements of the M960 test proposed to decrease false resistant results were based on the use of reduced inoculum densities of Mtb cells, to be easily translated into laboratory practice.

MeSH terms

  • Antitubercular Agents / pharmacology*
  • Culture Media / chemistry
  • Drug Resistance, Bacterial
  • False Positive Reactions
  • Humans
  • Hydrogen-Ion Concentration
  • Microbial Sensitivity Tests / methods*
  • Mycobacterium Infections / microbiology
  • Mycobacterium tuberculosis / drug effects*
  • Pyrazinamide / pharmacology*
  • Reproducibility of Results
  • Tuberculosis, Multidrug-Resistant / microbiology

Substances

  • Antitubercular Agents
  • Culture Media
  • Pyrazinamide