Phylogenetic relationship of Salmonella enterica strains in Tehran, Iran, using 16S rRNA and gyrB gene sequences

Abstract

Introduction: We assessed whether 16S rDNA and gyrB gene sequences, alone or combined, were suitable for determining the phylogenetic relationship among Salmonella enterica strains isolated from Tehran, Iran.  Patients over five years of age enrolled in an acute diarrheal surveillance project in Tehran province between May 2004 and October 2006 were selected as our study group.  Methodology: 16S ribosomal DNA (rDNA) and gyrB genes from 40 Salmonella isolates obtained from patients with acute diarrhea were sequenced and the data was used to generate phylogenetic trees that facilitated isolate comparison. Results: Salmonella strains clustered into five to seven phylogenetic groups, dependent on analysis of 16S rDNA (1546 bp), gyrB (1256 bp) or a combination of the two genes.  By 16S rDNA sequence analysis, only strains of Salmonella enterica  serovar Typhi ( S. Typhi)  clustered exclusively together.  gyrB sequences permitted clustering of all the S. Typhi and S. Paratyphi A isolates, and clustering of S. Enteritidis into two separate but exclusive groups.  Concatenation of the two data sets did not significantly improve the resolution of the strains compared to the gyrB gene.  None of the analyses completely resolved S. enterica Paratyphi B and C into mutually exclusive groups.   Conclusion: Sequencing of gyrB represents a potentially useful tool for determining the phylogenetic relationship of S. enterica strains in Tehran, Iran. Genetic analysis of the 16S rRNA gene alone or in combination with gyrB did not increase the resolution between serotypes of S. enterica.  We speculate that inclusion of additional genetic markers would improve the sensitivity of the analysis.