Bacterial infections represent the greatest threat for fish culture, especially those causing granulomatous processes. Although there are experimental models used to elucidate the mechanisms of pathogenicity in granulomatous processes, most of these aimed to understand the infection in superior vertebrates like humans; therefore, there is still an urgent need to expand the number of infection models focused on aquaculture. Granulomatous infections are difficult to detect in early stages due to the lack of clinical signs and because these clinical signs have a great similarity to those generated by other pathogenic bacteria. Besides, there is no evidence or reports of granulomatous co-infections in aquaculture environments which is a plausible scenario either in culture systems or in the wild environment; co-infections could interfere with a correct diagnosis of any granulomatous disease, as reported for granulomatous infections in terrestrial species. This revision aims to highlight the state of the art in the knowledge of pathogenic bacteria associated with granulomatosis in fish aquaculture as well as analysing this information.

Granulomatous diseases are caused mainly by bacterial infections that the fish immune system cannot eliminate; consequently, pathogens are encapsulated, forming a complex structure where immune cells participate in containing the damage.The granuloma is covered by a collagenous layer that may be an attractive surface for external bacteria, leading to the potential development of a microbiota associated with the outer side of granulomas. Therefore, this study aimed to describe the microbiota attached to and encapsulated by granulomas dissected from tilapia spleen obtained from a commercial farm. Tissue samples with an advanced granulomatosis stage were analyzed by amplifying and sequencing the V4 variable region of the 16S rRNA gene.More than 20 phyla were detected attached to granulomas; however, only five represented 94% of the relative abundance, and the genus Gordonia was the most abundant with 21.9%. This bacterium has been previously identified in the tilapia gut and has also been reported as the etiologic agent of granulomatous disease in humans and terrestrial animals. This is the first time it has been detected in fish granulomas. Finally, these results provide the first evidence of microbiota attached to granulomatous lesions while demonstrating that these can provide a surface that can harbour highly diverse microbial communities.

No abstract

No abstract