Pathogenicity and antibiotic susceptibility of Vibrio species isolated from moribund shrimps

The population of Vibrios in diseased Penaeus monodon collected from culture ponds situated at Uran, Maharashtra (west coast of India) was studied. All animals collected were associated with more than one Vibrio species. Bacterial identification based on morphological and biochemical characteristics showed that four groups of Vibrios were present in shrimp hepatopancreas namely Vibrio parahaemolyticus, V. alginolyticus, V. anguillarum and V. vulnificus. The diseased shrimps displayed poor growth, lethargic movements, red discolouration and mortality. Experimental infection of healthy P. monodon using the isolated Vibrios produced varying degrees of mortality. Antibiotic resistance of the isolated Vibrios were investigated. All the four species were sensitive to Erythromycin, Chloramphenicol and Streptomycin. However, V. parahaemolyticus and V. anguillarum showed resistance to Oxytetracycline and Polymyxin-B respectively and V. parahaemolyticus and V. vulnificus were resistant to ampicillin. Hence, antibiotic application to control vibriosis in shrimp farms may have limited effectiveness, based on the efficacy of the drug, because of the development of resistant strains of bacteria.