Comparison of two AFLP methods and PFGE using strains of Listeria monocytogenes isolated from environmental and food samples obtained from Piedmont, Italy.

Listeria monocytogenes ranks among the most frequent causes of death due to foodborne illness (20-30% case fatality rate). Discriminative subtyping methods are important to detect the relatedness of isolates and verify epidemiologic associations. AFLP analysis is a DNA fingerprinting technique based on the selective amplification of genomic restriction fragments. In this study, two AFLP methods and PFGE were compared in regard to discriminatory power, typeability and concordance. A total of 103 unrelated L. monocytogenes strains isolated from different environmental and food sources were analyzed. Strains were isolated from samples obtained from food-production plants, supermarkets and small food markets in Piedmont, Italy. All methods clustered L. monocytogenes strains into two genetic lineages, Lineage I and II. The three methods were compared using the 82 isolates which were typeable with all techniques. The calculated pair-wise Pearson's correlation coefficients (r) showed close agreement between all three methods. Our findings suggest that the AFLP II method can be successfully used to subtype L. monocytogenes strains isolated from foods and food processing facilities.