Novel microbiological system for antibiotic detection in ovine milk

This article presents a microbiological system composed of a “BT” bioassay (Beta-lactams and Tetracyclines) and a “QS” bioassay (Quinolones and Sulfonamides). The “BT” bioassay contains spores of Geobacillus stearothermophilus, bromocresol purple and cloramphenicol in a culture medium (incubation time: 2.45 h), while the “QS” bioassay uses spores of Bacillus subtilis, trifenyltetrazolium - toluidine blue and trimethoprim in a suitable culture medium (incubation time: 5.5 h). The detection capability (CCβ) of 27 antimicrobial agents in ovine milk were determined by logistic regression models. Thus, the “BT” bioassay detects amoxycillin, ampicillin, penicillin “G”, cloxacillin, oxacillin, cephalexin, cefoperazone, ceftiofur, chlortetracycline, oxytetracycline, tetracycline, neomycin, gentamycin and tylosin, while “QS” bioassay detects: ciprofloxacin, enrofloxacin, marbofloxacin, sulfadiazine, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfathiazole, erythromycin, lincomycin and spiramycin at levels close to their respective Maximum Residue Limits. The simultaneous use of both bioassays detects a large number of antibiotics in milk given each method's adequate complementary sensitivity.