In VivoAssessment of Drug Efficacy against Mycobacterium abscessusUsing the Embryonic Zebrafish Test System

ABSTRACTMycobacterium abscessusis responsible for a wide spectrum of clinical syndromes and is one of the most intrinsically drug-resistant mycobacterial species. Recent evaluation of the in vivotherapeutic efficacy of the few potentially active antibiotics against M. abscessuswas essentially performed using immunocompromised mice. Herein, we assessed the feasibility and sensitivity of fluorescence imaging for monitoring the in vivoactivity of drugs against acute M. abscessusinfection using zebrafish embryos. A protocol was developed where clarithromycin and imipenem were directly added to water containing fluorescent M. abscessus-infected embryos in a 96-well plate format. The status of the infection with increasing drug concentrations was visualized on a spatiotemporal level. Drug efficacy was assessed quantitatively by measuring the index of protection, the bacterial burden (CFU), and the number of abscesses through fluorescence measurements. Both drugs were active in infected embryos and were capable of significantly increasing embryo survival in a dose-dependent manner. Protection from bacterial killing correlated with restricted mycobacterial growth in the drug-treated larvae and with reduced pathophysiological symptoms, such as the number of abscesses within the brain. In conclusion, we present here a new and efficient method for testing and compare the in vivoactivity of two clinically relevant drugs based on a fluorescent reporter strain in zebrafish embryos. This approach could be used for rapid determination of the in vivodrug susceptibility profile of clinical isolates and to assess the preclinical efficacy of new compounds against M. abscessus.