A rapid turbidometric microplate bioassay for accurate quantification of lactic acid bacteria bacteriocins

Abstract

A 1 day turbidometric microplate bioassay (TMB) was developed for the rapid, accurate and precise quantification of lactic acid bacteria (LAB) bacteriocins (nisin Z and pediocin PA-1). Parameters such as the concentration of the indicator strains and the incubation time were optimized for each bacteriocin. A high correlation coefficient ( r 2=0.992±0.004) was obtained for the exponential regression in the nisin Z concentration range of 20–120 ng/ml with 1×10 7 CFU indicator strain ( Pediococcus acidilactici UL5) and an incubation time of 3 h. Using these parameters, the detection limit was estimated at 80 ng/ml (3.2 IU/ml), compared to 300 ng/ml for the agar diffusion assay (ADA). High precision (<7%) and accuracy (10%) were obtained for all nisin Z concentrations tested. Similar results were obtained with pediocin PA-1 with r 2=0.993±0.005, a precision (8.2%) and an accuracy lower than 15%.