Title: Conductimetric Analyses of Bacteriophage Infection of Two Groups of Bacteria in DL-Lactococcal Starter Cultures
Abstract: Two conductimetric methods were used for simple and rapid detection of bacteriophages against the two major groups of bacteria in DL-lactococcal, mixed-strain starter cultures.Bacteriophages against the acid-producing bacteria Lactococcus lactis ssp.lactis and Lactococcus lactis ssp.crenwris in a starter were analyzed in a Malthus@ instrument using reconstituted skim milk as the medium.The presence of phages against Lactococcus lactis ssp.lactis biovar.diacetylactis strains in a starter could be analyzed by measurement of C02 production with an indirect conductance method in the Rabi t @' instrument.For both methods, the presence of phages against bacteria in a starter increased the detection time.At 30'C and .l%inoculum, a very sensitive assay was obtained that detected phages against acid-producing strains in a starter within 3 to 4 h.The presence of 40 to lo00 infectious phages was sufficient for detection with a mixed-strain starter culture.Bacteriophages against C02producing bacteria were detected after 7 to 9 h with a .l%inoculum at 30°C.Bacteriophage infection of single strains of bacteria reduced total change in conductance.For pure strains of an acid-or a C02-producing strain, the detection limits were 1 and 100 pfu, respectively.