Correlating MIC with antimycobacterial efficacy against Mycobacterium abscessus

Abstract

BACKGROUND: The currently recommended treatment for Mycobacterium abscessus consists of a multidrug regimen based on drug susceptibility testing. Little is known about the relation between the drug susceptibility and in vitro efficacy of the antibiotics amikacin, tigecycline and linezolid, which are currently included in the guidelines. AIM: To investigate the correlation between minimum inhibitory concentrations (MICs) and in vitro bacterial killing of M. abscessus for amikacin, linezolid and tigecycline. METHODS: Clinical isolates of M. abscessus with varying MICs were used. MICs were determined by broth microdilution and time-kill assays were performed by exposing bacterial strains to static concentrations of each antibiotic. Bacterial densities were determined daily. Data was analysed by calculating the differences in the area under the curve between the exposed and control strains to evaluate antibiotic efficacy. RESULTS: A clear correlation between the MIC and bacterial killing was observed for amikacin, with a linear increase in antibiotic efficacy as the MIC decreased. In contrast, no correlation was observed for linezolid and tigecycline, which showed bacteriostatic activity for all tested strains regardless of MIC. CONCLUSION: The strong correlation between the MIC of amikacin and bacterial killing suggests that dosing could be optimised guided by MIC's to reduce toxicity and adverse effects. However, for linezolid and tigecycline, MIC-guided dosing is not practical and a standardised dosing could be suggested. Future research should validate these results in clinical settings to refine treatment protocols and improve patient outcomes.

Keywords

• Time-kill assay
• Antibiotic efficacy
• Mycobacterium abscessus