Microbiological inhibition method for determination of colistin residues in muscles of aquatic products

Bordetella bronchiseptica were extracted with methanol-0.1%formic acid water (volume ratio 3:7) under ultrasonication, purified by solid phase extraction column, and blowed with nitrogen gas. Then we used B.bronchiseptica to detect the residues after the concentration of samples. Results show that colistin in the muscle tissue of aquatic products ranged from 0.4 μg·mL^-1 to 2.4 μg·mL^-1, with good linearity between drug concentration logarithm and the diameter of bacteriostatic (R²> 0.990 0). Colistin in muscle was fortified at 0.20 μg·g^-1, 0.40 μg·g^-1 and 0.60 μg·g^-1, and the average recovery was 70.59%~70.59%, while the coefficient of variation was 3.22%~14.01%. The limits of determination were 100 μg·kg^-1 in grass carp and prawn muscles, 75 μg·kg^-1 in turtle and eel muscles, and 125 μg·kg^-1 in crab muscle. The cylinder plate method for determination of colistin residues is good. All minimum detection of drugs meet the national standard of residue limits issued by Ministry of Agriculture of China.