Comparative Phenotypic and Genotypic Properties of Serratia marcescens Isolates from Clinical Cases from human in AL-Diwaniyah Province, Iraq

Serratia marcescens is a Gram-negative, rod-shaped bacterium. It is an opportunistic and facultative anaerobe. This study aims to determine the occurrence rates of Serratia marcescens in human clinical samples, investigate the pigM gene, sequence the isolates, and compare them with global isolates documented in the NCBI database. Fifty burn samples were collected from the specialized center for burns in AL-Diwaniyah province, along with 35 urine samples from individuals suffering from UTIs from Al-Diwaniyah Teaching Hospital and various private laboratories. These samples were transferred in a cooled container to the microbiology lab at the Veterinary Medicine College, University of Al-Qadisiyah, for bacteriological assay. The samples were then cultured using selective and differential media. Following the purification of the cultured bacteria, biochemical tests were conducted to confirm the isolates. Results showed that 10 out of 85 samples (11.76%) were positive for Serratia marcescens. Culture positivity was most frequent in urine samples (17.1%), followed by burn samples (8%). Molecular methods revealed that human isolates gave 100% positive results for 16S rRNA. The study found that ten isolates of Serratia marcescens possess the pigM gene, with the 16S rRNA gene sequenced using the BLASTN algorithm of NCBI. All isolates were recorded under accession numbers (OR835629, OR835630, OR835631, OR835632, OR835633, OR835634, OR835635, OR835636, OR835637 and OR835638, showing 97-99% identity with isolates detected in China, India, and Nigeria. It can be concluded that the isolation rates of Serratia marcescens from urine samples are higher than those from burn samples. The sequencing results showed a 97-99% similarity with global isolates from China, India, and Nigeria.