ISOLATION AND IDENTIFICATION OF Vibrio SPECIES ASSOCIATED WITH GIANT FRESHWATER PRAWN Macrobrachium  rosenbergii CAPTURED FROM RESERVOIRS OF SRI LANKA

Bacteria consortiums, including Vibrio sp. associated with Giant Freshwater Prawn (GFP, Macrobrachium rosenbergii), are of utmost importance due to their diverse functionalities. The present study delves into the isolation, identification, and characterisation of a diverse array of Vibrio species associated with the GFP, collected from seven reservoirs, namely Bandagiriya Wewa, Mahagal Wewa, Ridiyagama Wewa, and Weerawila Wewa in Hambantota district, and Handapanagala Wewa,Muthukandiya Wewa, and Urusita Wewa in Monaragala district. All the samples were collected from fish landing sites in each reservoir. Then, following homogenization of individuals, they were cultured on Thiosulphate Citrate Bile Salt-Sucrose agar plates. The abundance of vibrios was enumerated using the spread plate method. Following the isolation, the colonies were identified with a battery of biochemical tests. Ability to form biofilms, and antibiotic resistance of isolated vibrios were also investigated as the final steps of  the experiment. Meanwhile, physicochemical parameters, temperature, pH, conductivity,  dissolved Oxygen, Secchi disk depth, chlorophyll-a content, and organic matter content of each  reservoir were measured to correlate them with the Vibrio abundance from each reservoir. The Kruskal-Wallis Pairwise comparison test was conducted to determine whether there is any  significant difference in the abundance of Vibrio sp. and the physicochemical parameters of  each reservoir. The abundance of Vibrio sp. associated with M. rosenbergii in Muthukandiya  Wewa (8.19±0.74 log CFU/g of prawn) was significantly higher than that of other reservoirs.  Temperature, pH, conductivity, chlorophyll-a, and organic matter content of the seven  reservoirs significantly varied. Among the recorded physicochemical parameters, the pH of  Urusita Wewa showed a strong positive correlation with the abundance of vibrios. A total of eleven Vibrio spp., namely V. proteolyticus, V. furnisii, V. metschnikovii, V. harveyi, V. litoralis, V. campbellii, V. ponticus, V. rumoiensis, V. natriegens, V. cholerae, and V. diazotrophicus, associated with GFP were identified. The microtiter assay revealed varying abilities of isolated  vibrios to form biofilms. Weak Biofilm Formers were higher in all tested post incubation times, followed by Moderate Biofilm Formers, Non-Biofilm Formers, and Strong Biofilm Formers. All the isolates were resistant to amoxicillin 10µg, ampicillin 10µg, and penicillin 10µg. ciprofloxacin 10µg was the most effective antibiotic against isolated vibrios, followed by cefixime 05µg, tetracycline 30µg, sulphamethoxazole/ trimethoprim 25µg, chloramphenicol  30µg, and streptomycin 10µg. The outcome of the present study is a bombshell to the scientific community as well as the fisheries communities engaged in Culture-Based fisheries of GFP,  since it provides insight into one of the major bacterial genera, which can be both beneficial and harmful for the growth of GFP. The findings on antibiotic resistance will be advantageous in disease management approaches to ensure higher productivity of GFP.      

Keywords: Antibiotic Resistance, Biochemical tests, Biofilm formation, Macrobrachium rosenbergii, Vibrio sp.