A total of 1,050 strains of heterotrophic bacteria isolated from farming seawater and the intestines of
oyster species Crassostrea hongkongensis were tested for resistance to 10 antibiotics by the Kirby–Bauer
diffusion method. The resistant rates of seawater-derived bacteria to chloramphenicol, enrofloxacin, and
ciprofloxacin were low (less than 20%), whereas the bacteria obtained from oysters showed low
resistance to chloramphenicol and enrofloxacin. Many strains showed high resistant rates (more than
40%) to furazolidone, penicillin G, and rifampin. A total of 285 strains from farming seawater and oysters
were resistant to more than three antibiotics