Abstract
One hundred seventy-five Listeria monocytogenes strains were characterized by serotyping, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) based on loci in actA, betL, hlyA, gyrB, pgm, and recA. One hundred twenty-two sequence types (STs) were identified by MLST based on allelic profiles of the four housekeeping genes (betL, gyrB, pgm, and recA), and 34 and 38 alleles were identified for hlyA and actA, respectively. Several actA and hlyA alleles appeared to be predominantly associated with clinical isolates. MLST differentiated most of the L. monocytogenes strains better than did PFGE, and the discriminating ability of PFGE was better than that of serotyping. Several strains with different serotypes were found, by MLST and PFGE, to have very closely related genetic backgrounds, which suggested possible "antigen switching" among them. MLST can be a useful typing tool for differentiating L. monocytogenes strains (including strains undistinguishable by PFGE typing and serotyping), and it may be of value during investigations of food-borne outbreaks of listeriosis.