Thesis (M.Sc.)--Chulalongkorn University, 2008

A total of 83 Vibrio isolates from farmed marine shrimps, comprising V. parahaemolyticus (n=26), V. cholera (n=8), V.fluvalis (n=23) and V. vulnificus (n=16) were included in this study. Susceptibilities to 10 antimicrobials were determined. The occurrence and characteristics of class1, 2 and 3 integrons were investigated. The presence of tet(K), tet(L), tet(M), tet(O) and tet(S) genes were examined. Seventeen isolates resistant to ciprofloxacin and/or enrofloxacin were examined for mutations the Quinolone Resistance Determinig Regions (QRDRs) of gyrA and parC genes. Seventy-four isolates (89%) were resistant to at least one antibiotic and 17 isolates (21%) were multidrug-resistant. Most of the Vibrio isolates (62%) were resistant to ampicillin and the most common resistance pattern was the AMP-SMX-TMP (4.82%). As class 1 integrons were identified in 6%, no class 2 and 3 intrgrons were detected. Only one class 1 integrons in a V. cholera isolate carried gene cassettes. Nucleotide sequrncing analysis revealed that the inserted gene cassette was the partial rumA gene. All of class 1 integrons did not harbor the typical 3’conserved segment. None of the isoloates possessed tet genes tested. As Ser-83-lle substitution in GyrA was the major mutation identified in the fluoroquinolone-resistant isolates (59%), no mutation in ParC was observed. The results warranted further studies to investigate other mechanisms underlying resistance to antibiotics in the Vibrio isolates from farmed marine shrimps.