Virulence of Vibrio alginolyticus isolated from diseased tiger prawn, Penaeus monodon

Outbreaks of mass mortality among cultured tiger prawns (Penaeus monodon) with white spotted syndrome (WSS) in the carapace occurred in the summer of 1994 in I-Lan, Taiwan. A swarming strain Val was isolated from hemolymph of the moribund prawns with tryptic soy agar (TSA, supplemented with 1% NaCl, Oxoid) and/or thiosulfate citrate bile salt sucrose (TCBS, Difco) agar. This strain was characterized and identified to be Vibrio alginolyticus. The strain was susceptible to antibiotics such as chloramphenicol, ciprofloxacin, doxycycline hydrochloride, nalidixic acid, oxolic acid, and oxytetracycline while resistant to ampicillin, novobiocin, penicillin G, sulfisoxazole, and sulfonamide. The bacteria and their extracellular products (ECP) were lethal to both tiger prawns (P. monodon) and kuruma prawns (P. japonicus) with LD50 values of 1.13 x 10(5), 2.46 x 10(5) CFU/g, and 0.23, 0.63 micrograms protein/g prawn body weight, respectively.