Evaluation of an rDNA Listeria probe for Listeria monocytogenes typing

A Listeria monocytogenes DNA fragment, identified as part of the 23S rRNA g ene and called B17, was used to type 266 L. monocytogenes strains and 43 st rains of other Listeria species. Results were compared with those obtained: i) with pBA2 (which consists of a 2.3 kb Bacillus subtilis DNA fragment en coding 16S rRNA, inserted into the HindIII site of pBR322), a probe previou sly used for Listeria and L. monocytogenes ribotyping, and ii) with DNA mac rorestriction profiles analysis. Twenty profiles were identified for L. mon ocytogenes using pB17, three of which accounted for 87% of strains. This ne w rDNA probe had greater discriminatory power for serogroups 1/2 or 3 strai ns than for serogroup 4 strains. The number of varieties and the discrimina tion index were higher with this new probe than with pBA2, but DNA macrores triction patterns analysis gave better discrimination between strains.