LAUSR

Abstract Motile Aeromonas Septicemia (Aeromonas hydrophila) has caused severe economic loss in several aquaculture fish species such as carps, tilapia, salmon, and catfishes. In the present study, mass mortality of zebrafish (Danio rerio) was observed in fish maintained in the hatchery cum rearing center, along with clinical signs including enlarged abdomen and haemorrhages on the body surface. The etiological agent was identified as Aeromonas hydrophila through biochemical and molecular methods. The isolated A. hydrophila, AhZ1K was positive for all the phenotypic virulence factors and cytopathic effect was observed in D. rerio gill (DRG) cell line. Further, A. hydrophila, AhZ1K was found to produce biofilm and was positive for eight virulence genes and five antibiotic resistance genes with a Multiple Antibiotic Resistance (MAR) index of 0.6 and 0.825 for free and biofilm cells respectively, indicating the property of multidrug resistance. Therefore, as a preliminary approach to develop bio-control measure, novel lytic bacteriophages (phages namely AhFM4 & AhFM5) were isolated from Western Ghats riverine water systems. Transmission electron microscopy (TEM) confirms that both the lytic phages (AhFM4 & AhFM5) belong to Myoviridae. Interestingly, AhFM4 & AhFM5 displayed 96% and 70%; 15 and 25 min; 152 ± 27 PFU/host cell and 112 ± 13 PFU/host cell of adsorption, latency and burst size respectively. The phages were stable over a broad array of physicochemical parameters (temperatures, salinity, and pH), indicating that AhFM4 and AhFM5 have an immense capability to be developed as a substitute for antibiotics to control motile Aeromonas septicemia in aquaculture.