title: Optimization of bioassay for tetracycline detection in milk by means of chemometric techniques.
abstract: OBJECTIVE
  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).
  
  
  RESULTS
  In a first stage, the response time of bioassay was reduced to 5 h 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 μg l(-1)) and oxytetracycline (100 μg l(-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 μg l(-1).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Cátedra de Biofísica, Departamento de Ciencias Básicas, Facultad de Ciencias Veterinarias, Universidad Nacional del Litoral, Esperanza, Argentina.
authors.forename: O G
authors.initials: OG
authors.lastname: Nagel
authors.forename: M P
authors.initials: MP
authors.lastname: Molina
authors.forename: R L
authors.initials: RL
authors.lastname: Althaus
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D001409:Bacillus cereus / Q000187:drug effects; D001681:Biological Assay / Q000379:methods*; D002701:Chloramphenicol / Q000737:chemistry; D005504:Food Analysis / Q000379:methods*; D057230:Limit of Detection; D016015:Logistic Models; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013171:Spores, Bacterial / Q000187:drug effects; D013754:Tetracyclines / Q000032:analysis*
chemical_list: D000900:Anti-Bacterial Agents; D013754:Tetracyclines; D002701:Chloramphenicol