CHARACTERIZATION OF LISTERIA-MONOCYTOGENES ISOLATES BY ESTERASE ELECTROPHORESIS

Multiple bands of alpha-naphthyl-propionyl esterase (alpha NPE) activi ty observed following starch gel electrophoresis of cell extracts allo wed 219 Listeria monocytogenes isolates from milk, nondairy foods, and clinical and veterinary sources to be assigned to 17 different alpha NPE types. Multilocus enzyme electrophoresis (MEE) analysis was used t o obtain electrophoretic mobility data for alpha NPEs and nine other m etabolic enzymes; on the basis of these data, the 219 strains were ass igned to 59 electrophoretic types. Each of the methods separated the s trains into two main groups, and there was extensive agreement on assi gnment of the strains to the groups. Although the method is less discr iminatory than MEE, the usefulness of alpha NPE electrophoresis alone as a rapid, simple typing method for L. monocytogenes for certain purp oses is indicated by agreement among alpha NPE, MEE, and restriction f ragment length polymorphism types as molecular markers for persistent and transient L. monocytogenes strains found in sequential raw-milk an d nondairy food samples obtained from different processors.