BACTERIOCIN QUANTIFICATION BY THE CRITICAL DILUTION METHOD - A COMPARISON OF ARBITRARY UNITS WITH DIAMETER AND AREA OF THE ZONE OF GROWTH-INHIBITION

Bacteriocin activity present in 6 solutions prepared from a culture of nisin-producing Lactococcus lactis subsp. lactis ATCC 11454 was estim ated by the critical dilution method, plates being read by 5 analysts. Bacteriocin activity was expressed in arbitrary units, calculated as the reciprocal of the highest two-fold dilution showing a definite zon e of growth inhibition, and by procedures based on the diameter or the area of the zone. From the regressions of bacteriocin activity determ ined by the various procedures on actual bacteriocin concentration, it was concluded that arbitrary units (r(2) = 0.385) were less accurate than procedures based on the diameter or the area of zones of growth i nhibition (r(2) = 0.825 - 0.932). Moreover, arbitrary units was the mo st subjective procedure, as it showed the highest influence of the ana lyst (P <0.001) on the quantification of bacteriocin activity.