Heat Treatment Effects on the Antimicrobial Activity of Macrolide and Lincosamide Antibiotics in Milk

Abstract

[EN] Aims: In this study, a microbiological method of dichotomous response using Bacillus cereus was designed and optimized to detect tetracyclines (TCs) at concentrations near to the maximum residue limits (MRLs). Methods and Results: In a first stage, the response time of bioassay was reduced to 5h when the logarithm of spore concentration (log S) was increased. Later, a Plackett Burman design (2 6-3) was analysed using logistic regression model. This design indicates significant effects of log S and chloramphenicol (CAP) on the detection limit (DL) of TC. Then, the response surfaces (RS) of the TCs DTs as a function of log S and CAP were plotted using a Dohlert design and the logistic regression model. These RS show a linear decrease with the raise of CAP and a quadratic effect of log S. Finally, the DTs of TC (109¿gl -1) and oxytetracycline (100¿gl -1) were adjusted to their MRLs through the desirability function. Conclusions: By successive application of experimental design techniques could be optimized a bioassay for the detection of TC residues in milk. The best conditions have been achieved when the assay was made with log S=5·12 and CAP=470¿gl -1. Significance and Impact of the Study: Experimental design techniques together with the logistic regression model and the desirability function represent an adequate tool for the optimization of a bioassay with binary response. © 2011 The Authors. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.