Expression of Surface Protein LapB by a Wide Spectrum of Listeria monocytogenes Serotypes as Demonstrated with Anti-LapB Monoclonal Antibodies

Protein antigens expressed on the surface of all strains ofListeria monocytogenes and absent from nonpathogenicListeria spp. are presumably useful targets for pathogen identification, detection, and isolation using specific antibodies (Abs). To seek such surface proteins expressed in various strains ofL. monocytogenes for diagnostic applications, we focused on a set of surface proteins known to be involved or putatively involved inL. monocytogenes virulence and identifiedListeria adhesion protein B (LapB) as a candidate based on the bioinformatics analysis of whole-genome sequences showing that the gene coding for LapB was present inL. monocytogenes strains and absent from strains of otherListeria spp. Immunofluorescence microscopy (IFM), performed with rabbit polyclonal antibodies against the recombinant LapB protein (rLapB) ofL. monocytogenes serotype 4b strain L10521, confirmed expression of LapB on the surface. A panel of 48 mouse monoclonal antibodies (MAbs) to rLaB was generated, and 7 of them bound strongly to the surface ofL. monocytogenes cells as demonstrated using IFM. Further characterization of these 7 anti-LapB MAbs, using an enzyme-linked immunosorbent assay (ELISA), revealed that 6 anti-LapB MAbs (M3484, M3495, M3500, M3509, M3517, and M3519) reacted strongly with 46 (86.8%) of 53 strains representing 10 of the 12 serotypes tested (1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4ab, 4b, 4d, and 4e). These results indicate that LapB, together with companion anti-LapB MAbs, can be targeted as a biomarker for the detection and isolation of variousL. monocytogenes strains from contaminated foods.IMPORTANCE Strains ofL. monocytogenes are traditionally grouped into serotypes. Identification of a surface protein expressed in all or the majority of at least 12 serotypes would aid in the development of surface-binding monoclonal antibodies (MAbs) for detection and isolation ofL. monocytogenes from foods. Bioinformatics analysis revealed that the gene coding forListeria adhesion protein B (LapB), a surface protein involved inL. monocytogenes virulence, was present inL. monocytogenes strains and absent from otherListeria spp. Polyclonal antibodies against recombinant LapB (rLapB) detected the exposed epitopes on the surface ofL. monocytogenes . Production and extensive assessment of 48 MAbs to rLapB showed that 6 anti-LapB MAbs (M3484, M3495, M3500, M3509, M3517, and M3519) detected the expression of LapB in a wide range ofL. monocytogenes isolates representing 10 of 12 serotypes tested, suggesting that LapB, together with specific MAbs, can be targeted as a biomarker for pathogen detection and isolation.