Detecção de genes dos Sistemas de Secreção dos Tipos II, III e VI em Aeromonas spp. isolados de peixes ornamentais doentes na Mesorregião da Zona da Mata Mineira

Abstract

The ornamental fish market is one of the fastest-growing segments of aquaculture, driven by the sector’s development and high economic potential. However, the intensification of production has posed significant health challenges, favoring the spread of bacterial diseases that directly impact the production chain. Among the pathogens most frequently associated with infections in ornamental fish, Aeromonas spp. stand out as opportunistic bacteria with a wide environmental distribution and diverse range of hosts, causing mortality and significant economic losses in fish production. In this study, strains of Aeromonas spp. were isolated and characterized from diseased ornamental fish collected in the Mesoregion of Zona da Mata, Minas Gerais. Additionally, genes related to secretion systems (T2SS, T3SS, and T6SS) were detected. Initially, all bacterial isolates were analyzed by MALDI-ToF MS, allowing for rapid screening and selection of Aeromonas strains. However, due to this technique’s limitations in species-level differentiation, molecular methods were employed to confirm the identity of the isolates. Multiplex PCR (m-PCR), species-specific PCR for A. caviae, and sequencing of the rpoD gene were performed to ensure more accurate identification. The m-PCR enabled the detection of A. hydrophila, A. veronii, A. dhakensis, and A. jandaei among the analyzed isolates. Only one isolate was confirmed as A. caviae. Furthermore, for six isolates, species identification was only possible through rpoD gene sequencing. A. veronii and A. hydrophila were the most frequently detected species in the diseased fish. Virulence genes associated with type II (T2SS), type III (T3SS), and type VI (T6SS) secretion systems were widely detected, with the act gene from T2SS and vgrG2 and hcp2 from T6SS being the most frequent, suggesting a pathogenic potential of the isolated strains. These findings reinforce the importance of continuous monitoring and the adoption of strict biosecurity measures in ornamental aquaculture to mitigate the negative impacts of pathogen dissemination within the production chain. Molecular techniques proved to be an effective approach for the species-level identification of Aeromonas and the detection of virulence genes, contributing to the improvement of health management protocols in ornamental aquaculture.