Bioassay for nisin in milk, processed cheese, salad dressings, canned tomatoes, and liquid egg products.
A sensitive nisin quantification bioassay was constructed, based on Lactococcus lactis chromosomally encoding the nisin regulatory proteins NisK and NisR and a plasmid with a green fluorescent protein (GFP) variant gfp(uv) gene under the control of the nisin-inducible nisA promoter. This strain, LAC275, was capable of transducing the signal from extracellular nisin into measurable GFPuv fluorescence through the NisRK signal transduction system. The LAC275 cells detected nisin concentrations of 10 pg/ml in culture supernatant, 0.2 ng/ml in milk, 3.6 ng/g in processed cheese, 1 ng/g in salad dressings and crushed, canned tomatoes, and 2 ng/g in liquid egg. This method was up to 1,000 times more sensitive than a previously described GFP-based nisin bioassay. This new assay made it possible to detect significantly smaller amounts of nisin than the presently most sensitive published nisin bioassay based on nisin-induced bioluminescence. The major advantage of this sensitivity was that foods could be extensively diluted prior to the assay, avoiding potential inhibitory and interfering substances present in most food products.
Hakovirta
J
J
Department of Applied Chemistry and Microbiology, Viikinkaari 9, FI-00014 University of Helsinki, Finland.
Reunanen
J
J
Saris
P E J
PE
D000818:Animals; D001681:Biological Assay / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D002611:Cheese / Q000032:analysis; D003212:Condiments / Q000032:analysis; D004269:DNA, Bacterial / Q000235:genetics; D004531:Eggs / Q000032:analysis; D005504:Food Analysis / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D005511:Food Handling; D005520:Food Preservatives / Q000032:analysis* / Q000592:standards; D005798:Genes, Bacterial; D049452:Green Fluorescent Proteins / Q000235:genetics; D013294:Lactococcus lactis / Q000235:genetics; D018551:Solanum lycopersicum / Q000737:chemistry; D008892:Milk / Q000737:chemistry; D009561:Nisin / Q000032:analysis* / Q000235:genetics / Q000592:standards; D012015:Reference Standards; D012680:Sensitivity and Specificity
D004269:DNA, Bacterial; D005520:Food Preservatives; D009561:Nisin; D049452:Green Fluorescent Proteins