Detection of Mycobacterium marinum and multidrug-resistant bacteria in a chronic progressive disease outbreak among Siamese fighting fish (Betta splendens) in India

Siamese fighting fish (Betta splendens) is a popular aquarium ornamental fish in global trade. However, there have been increasing reports of infection in betta fish by bacterial and viral pathogens. In the present study, the causative agents of a chronic infection in betta from a private farm in Kerala, India were investigated. Culturable bacteria associated with the infected fish during the process of antibiotic treatment and their resistance profiles were evaluated. Phenotypic and genotypic characterization revealed 7 different bacterial isolates viz. Aquitalea pelogenes, Acinetobacter pittii, Bacillus cereus, Pseudomonas mosselii, Acinetobacter baylyi, Klebsiella variicola and Aeromonas veronii. Antibiotic susceptibility using disc diffusion technique revealed that all bacteria except A. pelogenes were multidrug-resistant and had a MAR index > 0.2. It was of great concern that even new generation antibiotics were ineffective towards A. pittii, and P. mosselii. Amplification and sequencing of mycobacterium specific hsp65 revealed the presence of Mycobacterium marinum in the infected fish. No cytopathic effects in the fish cell lines after 10 days post-inoculation of tissue homogenate filtrate from affected fish confirmed the absence of viral etiology. To the best of our knowledge, this is the first report of chronic M. marinum infection reported in Siamese fighting fish from Kerala, India. Further, the study recommends frequent monitoring of betta farms for bacterial pathogens, their antibiotic resistance profiles, proper maintenance and frequent survey of fish tanks for non-tuberculous mycobacteria as they pose zoonotic concern, and once established it is hard to be eliminated.

Automated summary

This study investigated the causative agents of chronic infection in betta fish from a private farm in Kerala, India, and found various bacteria and the presence of Mycobacterium marinum. The study recommends frequent monitoring of bacterial pathogens and antibiotic resistance in betta farms, as well as regular inspection of fish tanks.