Effect of probiotics, antibiotic sensitivity, pathogenicity, and plasmid profiles of Listonella anguillarum-like bacteria isolated from Penaeus monodon culture systems

Abstract

Occurrence of Listonella anguillarum-like bacteria was monitored in grow out ponds of the black tiger shrimp Penaeus monodon in 1996 and 1997. L. anguillarum-like bacteria were determined in source seawater and sediment, pond water and sediment, and in the shrimp tissue. L. anguillarum-like bacteria density was lower in source seawater than in shrimp culture pond water. Water, sediment, and shrimp tissue in the probiotic-treated ponds contained lower L. anguillarum-like bacteria densities than those in the untreated (control) ponds. Forty different isolates of L. anguillarum-like bacteria were identified, and their antibiotic sensitivity, pathogenicity, and plasmid profiles were determined. Pathogenicity experiments revealed that LD 50 values of 9×10 5 and 9×10 4 colony forming units (CFU) ml −1 of L. anguillarum-like bacteria produced mortality of intramuscular injected P. monodon and Penaeus indicus, respectively. Antibiotic resistance studies showed that 40 isolates of L. anguillarum-like bacteria were 100% resistant to Ampicillin, 80% to Chlortetracycline, and sensitive to Erythromycin (60%) and Gentamycin (70%). Plasmid profile analysis revealed that among the 40 isolates of L. anguillarum-like bacteria, only seven harboured plasmids ranging from 1.8 to 18.5 kb in size; the remaining 33 were devoid of plasmids.