High-frequency endonuclease (REA) typing: results from the WHO collaborative study group on subtyping of Listeria monocytogenes

Eighty isolates of Listeria monocytogenes were typed by high-frequency restriction endonuclease analysis. Two laboratories participated in the study with two restriction enzymes each. The enzymes used were EcoRI, Hae1II, HhaI, and its isoschizomer CfoI. EcoRI was less discriminatory than the other enzymes. The profiles generated by Hha1 and Cfo1 were not fully stable for some closely related isolates. The size and the number of restriction bands generated by Hha1 in one laboratory and its isoschizomer Cfo1 in another laboratory were directly comparable. This indicates that REA-typing may be used as a definitive typing method for Listeria monocytogenes if the typing procedure is standardized. The stability of the REA-types needs further elucidation in order to establish firm differentiation criteria for comparison of isolates.