Microbial System for Identification of Antibiotic Residues in Milk
ORLANDO NAGEL1, PILAR MOLINA2 AND RAFAEL ALTHAUS1*
1. Cátedra de Biofísica, Departamento de Ciencias Básicas, Universidad Nacional del Litoral,
R.P.L. Kreder 2805. 3080 Esperanza, República Argentina.
2. Instituto de Ciencia y Tecnología, Universidad Politécnica de Valencia, Camino de Vera 14, 46071 Valencia, España.
(Received: August 18, 2010; Accepted: June 2, 2011)
ABSTRACT
The aim of this study was to evaluate the ResScreen® microbiological system for the identification of antibiotic residues in milk. This microbiological system consists of two methods, the BT (betalactams and tetracyclines) and BS (betalactams and sulfamides) bioassays, containing spores of G. stearothermophilus subsp. calidolactis, culture media and indicators (acid-base and redox). The detection limits of 29 antimicrobial agents were calculated using a logistic regression model.
Both methods detect residues of penicillin-G, ampicillin, amoxicillin, cloxacillin, oxacillin, cephalexin, cefoperazone and ceftiofur® at levels close to their Maximum Residue Limits (MRL). The BT bioassay also presents good sensitivity to tetracycline and oxytetracycline residues, whereas the BS bioassay detects sulfadiazine, sulfamethoxazole and sulfathiazole residues in milk.
The simultaneous use of both bioassays identifies betalactam, tetracycline and sulfamide residues in milk. Neomycin, tylosin and lincomycin residues can also be detected, but these molecules are positive with the BT and BS bioassays, e.g., betalactams, given the microorganisms’ sensitivity to these molecules.
Key words: screening test, microbiological inhibition system, betalactams, tetracyclines, sulfamides, milk