Genomic Characterization of a Multidrug-Resistant Serratia marcescens Isolate Recovered from a Neonatal Meningitis Case in Iraq.

Serratia marcescens (S. marcescens) is an opportunistic pathogen associated with severe hospital-acquired infections, particularly in neonatal intensive care units. Here, we report the first whole-genome sequencing and characterization of a multidrug-resistant S. marcescens isolate (NOA1) recovered from the cerebrospinal fluid of a neonate with acute meningitis in Iraq. The isolate was identified using the VITEK® 2 system and confirmed by 16 S rRNA gene sequencing. Antimicrobial susceptibility testing demonstrated a multidrug-resistant phenotype, with resistance to β-lactams, aminoglycosides, carbapenems, nitrofurantoin, and trimethoprim/sulfamethoxazole, while susceptibility to ciprofloxacin, levofloxacin, and tigecycline was retained. Whole-genome sequencing produced a 5.29 Mb draft genome with 59.67% GC content, an N50 of 1.35 Mb, and an average sequencing coverage of 200x. Genome analysis identified 15 antimicrobial resistance genes, including 10 located on plasmid-associated contigs, suggesting a potential role of mobile genetic elements in resistance dissemination. Comparative genomic analysis revealed 13,971 sequence variants relative to the closest available reference genome, indicating substantial genetic divergence. Phylogenetic analysis placed NOA1 within a distinct lineage of clinical S. marcescens isolates. This study highlights the utility of whole-genome sequencing for comprehensive characterization of multidrug-resistant S. marcescens and underscores the importance of integrating phenotypic and genomic approaches for accurate antimicrobial resistance profiling.