Inhibitory Activity of Antibiotics and Anti-Vibrio Probiotics Against Vibrio harveyi Isolated from Penaeid Shrimp Hatcheries

Abstract

In the present study, water samples were collected from different hatcheries during vibriosis outbreak. Overall, ten species of Vibrio were isolated on the basis of biochemical tests in which three were identified as Vibrio harveyi (C3, C5 and C9). Antibiogram of bacterial isolates were ascertained using the disk diffusion method and the result revealed that all three isolates were susceptible to ceftriaxone, chloramphenicol, ciprofloxacin, gentamycin, nalidixic acid, norfloxazin, oxolinic acid, oxytetracycline, polymyxin B, rifampicin and tetracycline whereas it rendered resistance to three antibiotics viz., ampicillin, erythromycin and kanamycin. A total of 12 probiotic bacteria were isolated from the gut of black tiger shrimp ( Penaeus monodon) in which four exhibited antagonistic activity against V. harveyi and they were identified belonging to Bacillus spp. (AVP03, AVP04, AVP07 and AVP11). Anti-vibrio activity of the probiotic cultures were tested using agar well diffusion method (zone of inhibition ranging from 13.40.6 to 19.00.1 mm) and the isolate, AVP07 was identified as most efficient probiont. Production of anti-vibrio (extracellular) compounds of AVP07 started from the late log phase (10.6 mm inhibition zone in 12 hr) and the highest activity was found in early and late stationary phase (17.1 mm in 18 hr and 16.9 mm in 24 hr). The culture filtrate (0.45 m) of probiont AVP07 also showed the cell lytic activity on heat killed (4 to 10 hr below 50% and 18 to 22 hr below 75%) and live cells (at 4 hr below 50% and 6 to 22 hr below 75%) of V. harveyi C5.