NEW METHODS FOR SCREENING LACTIC-ACID BACTERIA THAT PRODUCE BACTERIOCIN ACTIVE AGAINST LISTERIA-MONOCYTOGENES AND FOR DETERMINING BACTERIOCIN ACTIVITY

New methods using a microtiter plate for screening lactic acid bacteri a (LAB) that produce bacteriocin active against Listera monocytogenes, and determination of bacteriocin activity using Omnispec 4000 were de veloped. In Modified Oxford (MOX, Oxoid) medium, L. monocytogenes prod uces a black color around the growth. In this study inhibition of L. m onocytogenes by bacteriocin was determined using the color change of t he medium in a microtiter plate. Because each well of a microtiter pla te limits the spread of microbial growth activity, this method can ove rcome the disadvantage of the agar overlay method in which a large cle ar zone can cover other microorganisms that are not producing bacterio cin. This new method is rapid, simple, and economical. Among the 96 st rains of LAB isolated from meat 25 strains produced bacteriocin agains t L. monocytogenes. The Omnispec 4000 was used to automatically record color changes due to the growth of L. monocytogenes in MOX medium con taining six different concentrations of Nisin (bacteriocin) in wells o f a microtiter plate. Depending on bacteriocin activities (IU). the sl opes of the color changes recorded were different. The bacteriocin act ivities were determined easily and accurately by using the slopes to c onstruct a calibration curve (r(2)=0.96).