Decoding the Virulence by sequencing analysis: Investigating Key Genes in Salmonella Typhi Isolates from Baghdad

Typhoid fever is one of the most important problem of global health in the developing countries, and the pathogenicity of Salmonella enterica serovar Typhi ( S . Typhi) depends on possession of different virulence factors, this study amid to investigate the spread of virulence genes among S. Typhi isolates from patients with typhoid fever in Baghdad, Iraq. Sixty S. Typhi isolates were collected from several hospitals in Baghdad. All isolates identified by vitek-II and then identification confirmed by PCR to detect 16S rRNA gene. The susceptibility test to different antimicrobials performed by method of disk diffusion, the results found the highest resistance rate (100%) to Ampicillin, Piperacillin, Cefotaxime and Ceftriaxone in contrast, the highest sensitivity rate (100%) found to Ertapenem, Imipenem, Meropenem and Sulfamethoxazole \Trimethoprim. The presence of genes encoding for virulence in S. Typhi isolates was tested by conventional PCR and the result found out of 60 S. Typhi isolates, 59 (98.3%), 59 (98.3%), 58 (96.7%) (Significant differences (< 0.01)), and 60 (100%) were positive for viaB, staA, cdtB and orfL genes, respectively. Sequencing of PCR products were carried out in the Macrogen Company (Seoul/ Korea), and the sequences compared to the nucleotide sequences in Gen-Bank database / BLAST. Also the phylogenetic analyses of 16S rRNA, viaB, staA and cdtB based on the sequences of these genes were done and results found highly similarity of local sequences to the closely related sequences of genes in GenBank by using MEGA11 software. According to this results, presence of viaB, staA, cdtB and orfL virulence genes in almost isolates under study play an important role in the pathogenicity of local isolates.