Introduction
Nocardiosis caused by diverse, cosmopolitan aerobic actinomycetes species of the genus Nocardia is a common disease in several aquaculture species. In the Canary Islands, Spain, variated internal granulomas resembling those produced by nocardiosis were unexpectedly observed in cultured meagre (Argyrosomus regius ). Hence, we aimed to identify the causative species and experimentally reproduce the disease.
Material and Methods
Following classical methods, the bacterium was isolated from granulomas in the liver of several specimens and identified using 16S-rRNA gene sequencing and MALDI-TOF MS. The local in silico alignments with known 16S-rRNA sequences revealed the target identity as Nocardia brasiliensis , a species never before reported affecting fish. The virulence of this species was experimentally characterized in vivo . Juvenile meagre intraperitoneally infected with N. brasilensis develop internal micro granulomas without gross external sign or significant mortalities. Fish exposed to concentrations lower than 106 CFUs did not die at all within the two months trial. Five types of microscopic granulomas with classic necrotic centers and macrophages arranges were recorded in a dose-dependency fashion. Besides, immunofluorescence revealed the presence of live bacteria withing some granulomas.
Results and Conclusion
To our best knowledge, this is the first report of Nocardia brasilensis as disease agent in marine cultured fish. Besides , these results show that N. brasilensis successfully colonizes internal fish organs and is sufficient to develop chronic granuloma disease in meagre.
Acknowledgements
This work has been funded by the EU seventh Framework Programme by the DIVERSIFY project 7FP-KBBE-2013-GA-602131.