Minimal inhibitory concentration of 5 chemotherapeutants against Vibrio bacteria and their transferring of R-Plansmid
1996
Lila Ruangpan | Suppachai Prapadsorn | Kulvara Sangrungruang (Department of Fisheries, Bangkok (Thailand). National Institute of Coastal Aquaculture)
Vibrio bacteria, a major problem of intensively cultured black tiger shrimp, Penaeus monodon typically cause massive mortalities. To control the diseases, a wide range of chemotherapeutants are applied. Among those, oxytetracycline (OTC) and oxolinic acid (OA) are the most commonly agents used in many shrimp culture areas of Thailand. This study aims to investigate the minimal inhibitory concentration (MIC) of wellknown chemotherapeutants against Vibrio spp. and naturally transferring of their plasmid resistance. During the period June 1994 to April 1995, MICs of OTC, OA, NFLX (norfloxacin), CP (chloramphenicol) and KM (kanamycin) against 135 Vibrio strains isolated from the sediment of black tiger shrimp ponds were conducted. These studies were based on the Japan Society of Chemotherapy method (1981). A serial two-fold dilution procedure was used to prepare the agents; concentration tests ranging from 0.0125 to 100 micro g/mL. The transfer of R-plasmid strains were detected using Escherichia coli (RC85) as a recipient strain (Aoki, et al 1974). Results indicated that MICs value of OTC, OA, NFLX, CP and KM ranged respectively from 0.025-100,0.0125-100,0.125-100,0.1-100 and 1.6-100 micro g/mL. The inhibitory concentration of these agents against 50 percent (IC50) of studied strains were observed at 12.5, 1.2, 9.45, 9.45, and 100 micro g/mL. IC90 values were recorded at 100, 17.5,75 37.5 and 100 micro g/mL respectively. Vibrio strains carrying R-plasmid encoded with resistance for OTC were detected in 2 of 40 resistant strains, whereas a single specimen out 20 strains encoded for CP-resistance. This MIC study reveales a large number of strains resistant to chemotherapeutants. The study also reveales a number of R-plasmids in naturally accurring Vibrio that encoded for drug resistance. Proper guidance of chemotherapy application is badly needed to educate shrimp farmers.
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