Isolation and Characterization of Bacteria Associated with Cultured Penaeus monodon Affected by Loose Shell Syndrome

Abstract

Seventy shrimps affected by loose shell syndrome (LSS), a major disease causing mass mor- talities in shrimp farms in north coastal Andhra Pradesh (India), were subjected to bacteriologi- cal analysis. Total bacteria and vibrio counts in the hemolymph were estimated; bacteria were isolated and identified; their pathogenicity and drug sensitivity were studied. Total bacteria ranged 1.28 x 102 to 5.8 x 105 cfu/ml while Vibrio ranged 0.7 x 102 to 2.1 x 105 cfu/ml. Six species of Vibrio were isolated from the hemolymph including V. harveyi, V. alginolyticus, V. para- haemolyticus, V. anguillarum, V. splendidus, and V. vulnificus. Vibrio harveyi was the most dom- inant with a prevalence of 100%. It was also the most virulent with a low LC50 value of 1 x 103 cfu/g. Histopathological study revealed changes typical of bacterial septicemia including invasion of bacteria into the hemolymph, formation of granulomas in the hepatopancreas and other organs, and extensive proliferation of connective tissue and necrosis of the hepatopancreas, gills, and ovarian tissues. Sensitivity to 22 antibiotics was tested. Most of the bacterial isolates were highly sensitive to chloramphenicol, ciprofloxacin, and norfloxacin while V. harveyi was resistant to as many as 16 antibiotic drugs including chloramphenicol.