Background: Macrobrachium rosenbergi, the giant freshwater prawn, is one of the most important commercially-produced crustaceans in Bangladesh. A significant limitation to the industry is loss of productivity due to the emergence of various pathogenic bacteria and viruses and their resistance to chemotherapeutic drugs, resulting in mass mortality and consequent crop failure. Finding public health and an environment-friendly alternative is, therefore, a burning question to ensure the sustainability of this industry in Bangladesh.
Objectives: Probiotics-the friendly bacteria with a host of benefits that work by competitive exclusion of pathogenic bacteria can be a suitable alternative. This cause the mortality of prawn.
Methods and Materials: following an outbreak of disease of prawn hatcheries of the Sathkhira and Khulna regions during May 2012, samples were collected immediately from dead prawn larvae, rearing water, and fish feed to isolate and characterize the pathogenic bacteria. The antibiogram of the isolated pathogens was conducted before they were challenged to complete with probiotic bacteria, Lactobacillus spp., isolated from curd. Results: the bacterial count was significantly higher (p<0.05) in the animal samples than that in the water and fish feed samples, indicating that mortality was due to bacterial infections. The dead animals harboured heavy loads of pathogenic bacteria and were identified as Vibrio spp. and Shigella spp. based on the morphological, biochemical physiological characteristics of the pathogens. Twenty-six antibiotics were tested to study the drug-resistance patterns of the isolates. All the tested isolates (n=36) showed remarkable resistance to virtually all the drugs tested ranging from moderate to complete resistance, and the highest sensitivity of the isolates (75%), however, was recorded for doxycycline. In an in vitro attempt to control the growth of pathogens of solid media, the cell-free supernatant (CFS) of the two-day-old lactobacillus spp., soaked in blanks discs clearly produced at least 15 mm zone of inhibition. In broth cultures, CFS, collected at intervals of different days, produced a dose- and age-dependent reduction of bacterial count. Conclusion: the inhibition of bacterial growth could be attributed of some extracellular substances released from lactobacillus spp., demonstrating its potential to be an excellent probiotic candidate for possible applications in prawn aquaculture. If successfully transferred to roaring environment, this will be an eco-friendly approach to counter bacterial infections without compromising the quality of prawn, thereby ensuring food safety in the prawn industries of Bangladesh.
Acknowledgement: The study was supported by the Department of Fisheries, Ministry of Fisheries and Livestock, and the Ministry of Science and Technology, Government of Bangladesh.
Abu Md. Ramim, Sabikunnahar, Shafiqur Rahman
Niamul Naser, and Muhammad Manjurul Karim (firstname.lastname@example.org)
Department of Microbiology and Department of Zoology, Faculty of Biological Sciences, University of Dhaka, Dhaka 1000, Bangladesh