Molecular identification of four Salmonella serovars isolated from food in Tunisia based on the sequence of the ribosomal RNA genes

In this study, the 5′-end of the 16S-23S intergenic spacer regions and domains II and III of the 23S ribosomal DNA (rDNA) of six Salmonella strains were analyzed. These strains belong to four serovars: Agona, Amesterdam, Corvallis and Enteritidis, and were isolated from food samples. Polymerase chain reaction (PCR) products were then sequenced on both strands and the sequences obtained were aligned using the “Clustal W” program. The comparative sequence analysis revealed that the 5′-end of the 16S-23S spacer region rDNA is highly conserved among the four Salmonella serovars tested. All of these sequenced spacer regions contained a tRNA Ile gene. For the domains II and III of the 23S rDNA, the sequence analysis showed the presence of both conservative and variable regions. Some mutations, substitutions and deletions were also detected. This work supports the hypothesis that the 23S rRNA genes are useful for the definition of serovar-specific probes for the detection of Salmonella in food.