Genomic typing of Listeria monocytogenes strains by automated laser fluorescence analysis of amplified fragment length polymorphism fingerprint patterns

Abstract

The genetic relationship between isolates of Listeria monocytogenes belonging to different serotypes was determined and the suitability of automated laser fluorescent analysis (ALFA) of amplified fragment length polymorphism (AFLP) fingerprints was assessed by genomic typing of 106 L. monocytogenes isolates belonging to serotypes 1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4a, 4ab, 4b, 4c, 4d, 4e, 1, and 7. Digitised AFLP fingerprints were obtained that showed approximately 50 clearly distinguishable selectively amplified EcoRI/MseI bands for each strain. The coefficient of similarity between the profiles was determined by simple matching (Ssm). Based on these coefficients of similarity the investigated strains clustered in two genomic groups. The first group consisted of strains belonging to serotype 1/2a, 1/2c, 3a and 4a, while the second group was comprised of strains belonging to serotypes 1/2b, 3b, 4ab, 4b, 4e and 1. The average simple matching coefficient of similarity between strains of the second group was 92%, which was 4% higher than within group 1. Hence, the serotypes which are responsible for the majority of the listeriosis cases, 1/2a, 1/2b and 4b, fall into two distinct genetic groups, in concordance with their flagellar antigen type. The discriminatory power of AFLP in combination with automation of the analysis of the fingerprint profiles by ALFA makes AFLP-ALFA highly suitable for typing L. monocytogenes.