Genotyping of Listeria monocytogenes: comparison of RAPD, ITS, and PFGE

Forty-eight strains of Listeria monocytogenes were genotyped by two rapid methods: random amplification of polymorphic DNA (RAPD) and 16S to 23S rRNA internal transcribed spacer fragment length polymorphism (ITS), and compared to the more time-consuming pulsed-field gel electrophoresis (PFGE). The strains originated primarily from either pigs, pork products, or pork product processing environments. With strict standardisation of procedures in two separate laboratories, we were able to obtain excellent inter- as well as intralaboratory RAPD typing reproducibility. RAPD typing employing two different PCR primers divided the strains into 10 RAPD types (index of discrimination of 0.793). ITS typing employing primers designed for conserved eubacterial rRNA sequences gave only two ITS types, and was therefore not suited for genotyping of L. monocytogenes. PFGE typing by ApaI-restriction of chromosomal DNA gave 15 PFGE types (index of discrimination of 0.910). Combination of RAPD and ITS typing gave an index of discrimination of 0.844. There was generally good agreement between the relatedness of strains and subgroups indicated by the three methods.