Comparative study on antibiogram of Vibrio spp. isolated from diseased postlarval and marketable-sized white leg shrimp (Litopenaeus vannamei)

Abstract

This paper compared antibiotic sensitivity between Vibrio spp. isolated from diseased postlarval and marketable-sized white leg shrimp (Litopenaeus vannamei). Recently, white leg shrimp become target species of shrimp culture among shrimp farmers in Malaysia to replace tiger shrimp (Penaeus monodon) culture. However, the baseline information on antibiogram of pathogenic bacteria especially Vibrio spp., the causative agent of vibriosis in white leg shrimp culture is not well established. Therefore, this study was conducted to reveal the antibiogram of Vibrio spp. isolated from diseased postlarval and marketable-sized white leg shrimp. The information gained from this study is useful for shrimp farmers in selecting appropriate antibiotic during disease outbreak. Antibiogram of present bacterial isolates was determined through disk diffusion method against 21 antibiotics (oxolinic acid 2 μg, ampicillin 10 μg, erythromycin 15 μg, furazolidone 15 μg, lincomycin 15 μg, oleandomycin 15 μg, amoxicillin 25 μg, colistin sulphate 25 μg, sulphamethoxazole 25 μg, chloramphenicol 30 μg, doxycycline 30 μg, florfenicol 30 μg, flumequine 30 μg, kanamycin 30 μg, nalidixic acid 30 μg, novobiocin 30 μg, oxytetracycline 30 μg, tetracycline 30 μg, nitrofurantoin 50 μg, fosfomycin 50 μg, and spiramycin 100 μg). A total of 47 Vibrio spp. isolates (Vibrio parahaemolyticus, 24, and V. alginolyticus, 23) from postlarval white leg shrimp and 49 Vibrio spp. isolates (Vibrio parahaemolyticus, 13, Vibrio alginolyticus, 28, and luminous Vibrio parahaemolyticus, 8) from marketable-sized white leg shrimp were successfully identified. Results of antibiotic sensitivity test from the present study showed that more than 80% Vibrio spp. from diseased postlarval and marketable-sized white leg shrimp, respectively, were sensitive to 14 out of the 21 tested antibiotics. Vibrio spp. isolated from marketable-sized white leg shrimp were found more susceptible to the tested antibiotics than Vibrio spp. isolated from postlarval white leg shrimp. This was due to 100% sensitive case against eight antibiotics found among Vibrio spp. isolated from marketable-sized white leg shrimp, whereas only three antibiotics were found sensitive to all Vibrio spp. isolated from postlarval white leg shrimp. Furthermore, the multiple antibiotic resistance (MAR) index indicated that marketable-sized white leg shrimp were not under high risk exposure to the tested antibiotics. On the other hand, the postlarvae were highly exposed to the tested antibiotics.