Characterization of Vibrio isolated from Mangrove crab, Scylla serrata larval cultures


by:Jessie O. Jimenez, Jerome G. Genodepa, Rowena E. Cadiz, Jean Rose H. Maquirang


This study was conducted to isolate and identify the putative pathogenic Vibrio species dominantly present during the first 10 days of mangrove crab, Scylla serrata larval culture and test the isolates’ susceptibility to antibiotics. Dominant colonies of Vibrio were periodically isolated based on their colonial morphology on thiosulfate citrate bile sucrose (TCBS) agar and nutrient agar supplemented with 2% NaCl (NA+) plates. Conventional biochemical and physiological tests revealed the existence of 4 dominant groups belonging to 4 species including V. campbellii, V. proteolyticus, V. alginolyticus and V. tubiashii. Furthermore, through 16S rRNA gene sequencing, the taxonomic position of each representative strain randomly selected from the 4 dominant groups of Vibrio spp. Was ascertained. Moreover, the in vitro susceptibility of the 4 representative Vibrio spp. to commercially available antibiotic discs including amoxicillin, oxolinic acid, tetracycline, kanamycin, ampicillin, trimethoprim and cefprozil were examined. Results showed that all four species were susceptible to tetracycline, oxolinic acid and trimethoprim, however, the susceptibility of V. campbellii and V. proteolyticus to trimethoprim were just intermediate. The susceptibility of the Vibrio isolates to the rest of the commercial antibiotic discs were either intermediate or resistant. In addition, the minimal inhibitory concentration (MIC) assay was conducted using oxytetracycline (OTC) concentrations ranging from 10 to 50 mg L-1. Results showed that V. tubiashii was susceptible to at least 10 mg L-1 OTC, while V. campbellii, V. alginolyticus and V. proteolyticus were susceptible to at least 30, 40 and 50 mg L-1 OTC respectively. Current data clearly indicate that OTC is a suitable candidate for the treatment and prevention of vibriosis in S. serrata larval culture with at least 50 mg L-1 required to inhibit all the four putative pathogenic Vibrio spp. tested.

Keywords: antibiotic susceptibility, Vibrio, crab larvae