Preparation of Agar Bead Embedded <em>Mycobacterium abscessus</em> to Inoculate Immunocompetent Mice Intratracheally

Robust mouse models of chronic infection with Mycobacterium abscessus, an environmental pathogen that preferably infects the lungs, are badly needed. Year-long multidrug therapies deliver unacceptably poor cure rates in patients, around 50%, hence the need for predictive preclinical tools to develop better antibiotics. However, immunocompetent mice are generally resistant to pulmonary infection by M. abscessus. Numerous attempts to establish a sustained infection with M. abscessus in immunocompetent mice have been reported in the literature. Among these, methods relying on agar bead-embedded bacteria inoculated into C57BL/6 mice via the intratracheal route have proven most promising. The major limitation of this approach is the technical challenge associated with the preparation of agar beads of reproducible size and bacterial numbers, followed by intratracheal inoculation. Here, we first provide a detailed description of an optimized protocol that delivers M. abscessus-loaded agar beads of optimal diameter and reproducible bacterial burden. Next, we provide a detailed protocol of intratracheal inoculation, optimized to avoid losses of beads and bacteria due to adherence to surfaces of the inoculation devices and to achieve reproducible pulmonary deposition of agar-embedded M. abscessus. The objective is to ensure ease of implementation and excellent lab-to-lab reproducibility.