Mycobacterium abscessus is the most pathogenic species among the predominantly saprophytic fast-growing mycobacteria. This opportunistic human pathogen causes severe infections that are difficult to eradicate. Its ability to survive within the host was described mainly with the rough (R) form of M. abscessus, which is lethal in several animal models. This R form is not present at the very beginning of the disease but appears during the progression and the exacerbation of the mycobacterial infection, by transition from a smooth (S) form. However, we do not know how the S form of M. abscessus colonizes and infects the host to then multiply and cause the disease. In this work, we were able to show the hypersensitivity of fruit flies, Drosophila melanogaster, to intrathoracic infections by the S and R forms of M. abscessus. This allowed us to unravel how the S form resists the innate immune response developed by the fly, both the antimicrobial peptides- and cellular-dependent immune responses. We demonstrate that intracellular M. abscessus was not killed within the infected phagocytic cells, by resisting lysis and caspase-dependent apoptotic cell death of Drosophila infected phagocytes. In mice, in a similar manner, intra-macrophage M. abscessus was not killed when M. abscessus-infected macrophages were lysed by autologous natural killer cells. These results demonstrate the propensity of the S form of M. abscessus to resist the host's innate responses to colonize and multiply within the host. Author summary: Mycobacterium abscessus, a fast-growing mycobacterium and an opportunistic pathogen, is a harmful bacterium for people with cystic fibrosis. It can subsist on two morphological forms: rough (R) and smooth (S). R-M. abscessus results from the irreversible transition of S-M. abscessus. While severe pulmonary infections are associated with the presence of the R form, S-M. abscessus is considered the infective form. How S-M. abscessus resists the host innate response before to establish an infection remains unclear. Using Drosophila, we observed that S-M. abscessus is rapidly internalized by Drosophila phagocytic cells and the bacterium grows in these latter. Thanacytes, another Drosophila immune cell population, respond to the infection by inducing a caspase-dependent apoptotic death of the infected phagocytes. However, S-M. abscessus resists this lysis of phagocytes and grows dramatically leading to a bacteremia, causing the death of the infected flies. We confirmed the ability of intracellular S-M. abscessus to resist the lysis of phagocytes in a mammalian host by infecting primary murine macrophages and bringing them into contact with autologous natural killer cells. In conclusion, our study demonstrates that S-M. abscessus shares with strict pathogenic mycobacteria, such as M. tuberculosis, the virulence trait to resist the host innate cytotoxic response. [ABSTRACT FROM AUTHOR]