Multiplex PCR for the identification and serotyping of L. monocytogenes isolated from sheep’s cheese-processing plants

Commonly used strategies to identify and to characterize L. monocytogenes (Lm) strains are based on conventional and PCR methods (Graves et al., 1999; Gasanov et al., 2005). Molecular methods have been developed in order to reduce the analysis time and to increase its specificity. Epidemiology studies conveniently classify Lm isolates from food and listeriosis cases into serotypes, and use this as an indicator of potential strain pathogenicity. The majority (>95%) of isolates from sporadic and epidemic human listeriosis cases belong to the serotypes 1/2a, 1/2b, 1/2c and 4b (Bubert et al., 1999; CDC, 2004; Evans et al., 2004; Le Monnier, 2005). The arrangement of antigenic determinants is strictly connected with phylogenetic evolution and a correspondence has been found between serotypes and these divisions on a molecular basis (Doumith et al., 2004b). Many other molecular techniques contribute to Lm subtyping (Gravesen et al., 2000; Aarnisalo et al., 2003; Doumith et al., 2004b; Zhang et al., 2004). In this study a multiplex PCR assay for Lm identification and subtyping was developed that relied on specific marker gene detection. The multiplex PCR was also used for molecular characterization of strains isolated from the environment and from the products of sheep milk cheese processing plants.