Molecular characterization of quinolones resistant Salmonella typhi isolates from patients infected with Typhoid fever in Al-Najaf province, Iraq

Background: The global spread of typhoid fever is still a major public health concern. Typhoid fever is a potentially fatal infection often treated with quinolones, especially fluoroquinolones. Resistance to quinolones antibiotics in Salmonella typhi has made it harder to treat and has led to more mortalities. In this study, we detected of the qnr genes (plasmid-mediated quinolone resistance PMQR) in S.typhi isolated from patients in two main hospitals in AL-Najaf province, Iraq and determined the clonal relatedness between S.typhi isolates carried qnr genes. Materials and Methods: Antimicrobial susceptibility tests were performed using the disc diffusion method to investigate the ability of S. typhi to the resistance of 10 antibiotics. Qnr genes (qnrA,qnrB,qnrS) were detected by PCR amplification, and clonal relatedness between S.typhi isolates harbor qnr genes was analyzed following multilocus sequence typing (MLST). Results: Out of 246 blood samples collected from patients with suspected typhoid fever, 32 (13%) cases of S. typhi were identified using culture methods and confirmed using an automated Vitek-2 system. The highest antibiotic resistance rates were for ampicillin (24/32; 75%) and levofloxacin (19/32; 59.3%). All isolated (100%) were susceptible to ceftriaxone, cefixime, imipenem, meropenem, and azithromycin. Among PMQR genes determinants, qnrA, qnrB, and qnrS were positive in (1/32; 3%), (4/32; 12.5%) and (3/32; 9.3%) of the isolates, respectively. ST19, ST34, and ST36 were identified in (5/8; 62.5%), (2/8; 25%), and 1 (1/8; 12.5%) in S. typhi isolates positive for qnr genes, respectively. Conclusion: The first study from Iraq demonstrated the presence of qnr genes in S. typhi clinical isolates. In comparison to qnrS and qnrA, the qnrB gene was more common. The first study used multilocus sequence typing (MLST) to identify the sequence types of S. typhi isolates from hospitals in Al-Najaf. The Majority of ST19 sequence type of S. typhi was found.