Review of methods for detection and characterization of non-tuberculous mycobacteria in aquatic organisms

Mycobacteriosis is an emerging and often lethal disease of aquatic organisms caused by several non-tuberculous mycobacteria (NTM) species. Early diagnosis of mycobacteriosis in aquaculture and aquatic settings is critical; however, clinical diagnoses and laboratory detection are challenging, and the available literature is scarce. In an attempt to fill the gap, here we review the most relevant approaches to detect and characterize mycobacteria in clinical specimens of aquatic organisms. Emphasis is given to recent advances in molecular methods used to differentiate NTM species spanning from targeted gene sequencing to next-generation sequencing. Further, given that there are major gaps in our understanding of the prevalence of the different NTM species, partially because of their distinct requirements for in vitro growth, we also reviewed the most relevant NTM species reported to cause disease in aquatic organisms and their specific in vitro growth conditions. We also highlight that traditional bacterial culture continues to be relevant for NTM identification, particularly in non-automated laboratories. However, for NTM species discrimination, a high level of accuracy can be achieved with MALDI-TOF MS and molecular approaches, especially targeted gene sequencing applied from clinical specimens or from pure NTM isolates.