Restriction fragment length polymorphism analysis of Listeria monocytogenes and its application to epidemiological investigations.

The restriction fragment length polymorphisms (RFLPs) of 64 random and potentially related strains of Listeria monocytogenes were analysed and compared using a probe comprised of two L. monocytogenes chromosome fragments cloned into a lambda vector. Twelve RFLP types were defined using 14 isolates of clinical origin, 42 food isolates and eight food associated environmental strains. Of the RFLP types, some were common to a particular serovar and source, whereas others were widespread amongst all serovars and sources. One of the two most common RFLP patterns was associated with serovar 1/2 isolates from food or the environment, whereas another dominant pattern was associated most commonly with serovar four isolates from all sources. The potential relationships between epidemiologically related strains were examined, with the analysis of types from a suspected listeriosis outbreak, from clinical maternal-foetal cases, and from an ice-cream factory environmental study. Serotyping alone was not a sufficient marker for the comparison of these strains whereas further discrimination of strains was possible with RFLP analysis.