Use of homoduplex ribosomal DNA spacer amplification products and heteroduplex cross-hybridization products in the identification of Salmonella serovars.

When the hypervariable 16S-23S intergenic spacer regions found in prokaryotic ribosomal DNA (rDNA) are amplified from conserved adjacent sequences, homoduplex double-stranded DNA structures and heteroduplex structures containing substantial regions of single-stranded DNA are generated. The electrophoretic separation of these structures results in product profile patterns, which may be organized into highly correlated pattern groups of ribosomal spacer and heteroduplex polymorphism (RS/HP) types. In a test panel of 380 Salmonella strains that were analyzed by this procedure, 36 unique RS/HP types were observed. Of the 28 serovars in the test group, 21 showed single characteristic RS/HP types. The remaining seven serovars each contained multiple RS/HP types, which were also unique to individual serovars. Formation of heteroduplex structures with a substantially reduced electrophoretic mobility was observed in 29 of the 36 RS/HP pattern types. Because the mobility of these heteroduplex structures is sensitive to intergenic spacer sequence composition, the presence of these structures adds an additional diagnostic feature that is extremely useful in the differentiation of Salmonella serovars. The RS/HP types show sufficient diversity to be useful in the identification of many commonly observed Salmonella serovars. This analytical procedure is simple to perform and is well suited to rapid and inexpensive screening of large numbers of Salmonella strains.