The sequence heterogenicities among 16S rRNA genes of Salmonella serovars and the effects on the specificity of the primers designed.

Previously, we have reported a 16S rDNA targeted polymerase chain reaction (PCR) method for the specific detection of Salmonella serovars [J. Appl. Bacteriol. 80 (1996) 659]. The target sites of its primers, i.e. 16SFI and 16SIII, according to the data in GenBank, were found mismatched to the corresponding sequences of some Salmonella serovars, such as those of S. Houten, S. Chingola, S. Bareilly, and S. Weltevreden. Accordingly, a PCR method using a nonspecific primer MINf combined with a primer modified from our 16SFI primer, i.e. the primer MINr, was developed and displayed better detection specificity [Int. J. Food Microbiol. 80 (2003) 67]. In this study, we show the sequence heterogenicity at the primer 16SFI targeting sites for some Salmonella serovars. Thus, the sequence used for designing of PCR primers might be just one of the several possible sequences. Such a situation may lead to the misjudgment on evaluation of the specificity of the primers if this was only based on the data in GenBank. Strains of the above described Salmonella serovars with target sequences from GenBank mismatched to the primer 16SF1 were reidentified and their PCR results were confirmed. Meanwhile, their 16SFI/16SIII primer annealing sites were sequenced and the sequences obtained were found completely and highly homologous to those of 16SFI and complementary to those of 16SIII primer, respectively.