Listeria monocytogenes serotype identification by PCR

Abstract

Serotyping is a universally accepted subtyping method for Listeria monocytogenes. Identification of the strain serotype permits differentiation between important food-borne strains (1/2a, 1/2b, and 4b) and provides a "gold standard" for comparing isolates analyzed in different labs and with different techniques. Although an efficient enzyme-linked immunosorbent assay serotyping protocol was described recently, identification of PCR serotyping primers would further increase the ease and accessibility of this classification system. Serotyping PCR primers were designed from variable regions of the L. monocytogenes genome. Three primer sets were used in conjunction with a previously described Division III primer set in order to classify 122 L. monocytogenes strains into five serotype groups [1/2a(3a), 1/2b, 1/2c(3c), 4b(d,e), and 4a/c]. Results of the PCR method agreed with those of the conventional slide agglutination method for 97, 100, 94, and 91% of strains belonging to serotypes 1/2a, 1/2b, 1/2c, and 4b, respectively.

FIG. 1.

PCR amplification results. Lane 1, 100-bp ladder; lanes 2 to 6, D1 and D2 multiplex primers, strains ILSI 3 (1/2a), ILSI 6 (1/2b), H9333 (1/2c), ILSI 1 (4b), and no template control, respectively; lanes 7 to 9, FlaA primers, strains ILSI 3, H9333, and no template control, respectively; lanes 10 to 12, GLT primers, strains ILSI 6, ILSI 1, and no template control, respectively.