Identification of bacterial agents causing mortality in postlarvae of giant freshwater prawn (Macrobrachium rosenbergii ) in south-west coastal districts of Bangladesh

Abstract

Following an incidence of freshwater prawn Macrobrachium rosenbergii postlarvae (PL) mortality in hatcheries in summer 2012, samples from dead PL, rearing water and prawn feed from two south-west coastal districts of Bangladesh were collected to isolate, identify and characterize the agents causing PL mortality. Antibiogram profile of sixteen randomly selected bacteria, isolated from dead PL, that grew on TCBS, to 20 different antibiotics belonging to 12 major groups revealed that the drug resistance pattern varied from moderate (56% to the drugs: ciprofloxacin, cefotaxime, nitrofurantoin, kanamycin) to complete (to penicillin, ceftazidime and oxacillin) level. To identify the isolates, amplified rDNA restriction analysis (ARDRA) classified them in to four groups, and RAPD (randomly amplified polymorphic DNA) typing yielded nine different types of isolates within these four ARDRA groups. The 16S rDNA gene sequences identified that the groups were genotypically diverse belonging to the bacterial species: Enterobacter cloacae, Klebsiella pneumoniae, Exiguobacterium profundum and Enterococcus casseliflavus, respectively, that all demonstrated their killing potential to PLs in a simulated environment. The study therefore identified four different bacterial pathogens, one of which, Exiguobacterium profundum is reported for the first here in Bangladesh, that demand special consideration for disease management strategy.