Emergence of human associated bacterial pathogens in Anabas testudineus reared in freshwater Biofloc systems

In India, biofloc systems for freshwater fish farming have encountered significant challenges, with many projects failing due to widespread disease outbreaks. This study investigates the causes of these outbreaks, revealing that unhygienic conditions play a major role in the emergence of new diseases. Focusing on Anabas testudineus, the study examines the link between poor biofloc management, reverse zoonosis, and antimicrobial resistance. Twelve pathogenic bacterial isolates were recovered from fish reared in biofloc environments and identified through morphological, biochemical, and molecular techniques. Among these, eight were gram-negative rods and four were gram-positive bacilli. Notably, molecular identification revealed that most of the isolates, including Enterobacter cloacae, Klebsiella aerogenes, Citrobacter werkmanii, and Acinetobacter seifertii, are primarily human pathogens, rarely reported in fish. These bacteria exhibited various exoenzyme activities, indicating their pathogenic potential. Antibiotic susceptibility testing revealed inherent resistance in most isolates, raising concerns about biofloc systems fostering antimicrobial resistance even without prior antibiotic exposure. The study also underscores the risk of reverse zoonosis, emphasizing the need for stronger biosecurity measures to prevent the transfer of pathogens between humans and fish.