Pathogenicity of Antibiotic Resistant/Sensitive Bacteria Vibrio spp. and Aeromonas spp.

Bacterial and viral diseases constitute a major factor limiting the successes of shrimp farming
industry. In this context, Identification of drug resistant pathogens and determination of the pathogenic
processes of shrimp are fundamental for further progress in the disease management. They could be
valuable in the evaluation of their epidemiology and control measures. Water samples from the
aquaculture environment were contaminated with Vibrio anguillarum, V. damsela, V. furnissii,
Aeromonas hydrophila and A. sobria. Both Vibrio spp and Aeromonas spp were shown to be
pathogenic and to cause mortality to the infected post larval P. monodon. Vibrio spp. were shown to
grow in TCBS agar, zobell’s marine agar and blood agar while Aeromonas spp. additionally exhibited
growth in blood agar with selective supplement ampicillin (10 μg/ml) and showed a zone of clearance
in DNase agar. LD50 values of V. anguillarim, V. damsela, V. funrissii, A. hydrophila and A. sobria to
post larval P. monodon were determined as 1.1 x 105, 2.7 x 105, 6.0 x 105, 8.5 x 104, and 7.5 x 104
bacterial cells/ml respectively. Ciprofloxacin and streptomycin were found to be the most effective
antibiotics in the reduction of the mortality of experimentally infected post larvae. The growth of Vibrio
spp was inhibited by nifurpirinol (prefuran) at 25 μg/ml, oxytetracycline at 13 μg/ml, erythromycin
phosphate at 4 μg/ml, chloramphenicol at 12 μg/ml, streptomycin at 2 μg/ml, and ciprofloxacin at 1
μg/ml. While the growth of Aeromonas spp was inhibited by nifurpirinol (prefuran) at 24 μg/ml,
oxytetracycline at 14 μg/ml, erythromycin phosphate at 5 μg/ml, chloramphenicol at 12 μg/ml,
streptomycin at 2 μg/ml, and ciprofloxacin at 1 μg/ml. Vibrio spp. was sensitive to o/129 vibriostatic
agent (150 μg) whereasAeromonas spp. was resistant to it. The pathogenic bacteria viz. Vibrio spp
and Aeromonas spp could be controlled to some extent with judicious use of effective antibiotics to
improve the health status of shrimp in culture conditions and can have a positive impact in the areas
of sustainable aquaculture environment and development.