Novel bioassay using Bacillus megaterium to detect tetracycline in milk.

Tetracyclines are used for the prevention and control of dairy cattle diseases. Residues of these drugs can be excreted into milk. Thus, the aim of this study was to develop a microbiological method using Bacillus megaterium to detect tetracyclines (chlortetracycline, oxytetracycline and tetracycline) in milk. In order to approximate the limits of detection of the bioassay to the Maximum Residue Limit (100µg/l) for milk tetracycline, different concentrations of chloramphenicol (0, 1000, 1500 and 2000µg/l) were tested. The detection limits calculated were similar to the Maximum Residue Limits when a bioassay using B. megaterium ATCC 9885 spores (2.8×10(8)spores/ml) and chloramphenicol (2000µg/l) was utilized. This bioassay detects 105µg/l of chlortetracycline, 100µg/l of oxytetracycline and 134µg/l of tetracycline in 5h. Therefore, this method is suitable to be incorporated into a microbiological multi-residue system for the identification of tetracyclines in milk.