Molecular Characterization of Virulence Genes in <i>Serratia marcescens</i> Isolates from Clinical Cases in Al-Diwaniyah, Iraq: A Cross-Sectional Study

Background and Aim: Serratia marcescens (S. marcescens) is a Gram-negative, facultative anaerobic bacterium belonging to the Serratia genus of clinical importance.It is an opportunistic pathogen associated with various human infections, including pneumonia, meningitis, wound and burn infections, respiratory tract infections, urinary tract infections, bacteremia, and eye infections.The purpose of this study was to assess the frequency of S. marcescens in different clinical infections and evaluate the major virulence genes responsible for its pathogenicity.Materials and Methods: Clinical specimens (n=200) were collected from urinary, wound, burn, and eye infections from patients referred to Al-Diwaniyah Teaching Hospital and private clinics of Al-Diwaniyah Governorate from March 11 to August 20, 2024.Bacterial isolates were initially identified by cultural, microscopic, and biochemical examinations and confirmed by the VITEK system.Molecular characterization was done by PCR amplification of PhlA, ShlA, and FlhD virulence genes.The 16S rRNA gene was identified as control.The validated isolates were deposited in NCBI GenBank.Results: Twenty S. marcescens isolates were obtained from 200 samples: 15 (75%) from urinary tract infections, 3 (15%) from wounds and burns, and 2 (10%) from eye infections.The FlhD, PhlA and ShlA genes were found in 100%, 80%, and 35% of the isolates. Conclusion:The study emphasized that identification of major virulence determinants such as FlhD, PhlA, and ShlA enhances our understanding of S. marcescens pathogenicity in the studied region and provides a molecular basis for future epidemiological and clinical research.