Genomic and phenotypic characterization of a clinical Serratia bockelmannii isolate from Ibarra, Ecuador

This study reports the genomic and phenotypic characterization of a clinical Serratia isolate recovered from a tracheal aspirate in an intensive care unit in Ecuador. Although initially identified as Serratia marcescens by MALDI-TOF, average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) reclassified the isolate as Serratia bockelmannii. Whole-genome sequencing revealed a 5,027,153 bp genome with 59.50% GC content. Kirby-Bauer disk diffusion showed resistance to several β-lactams, aminoglycosides, and tetracycline, while susceptibility was retained to carbapenems and fluoroquinolones. Genomic analysis identified a limited set of resistance determinants (blaSRT-4, aac(6')-Serra, and tet(41)), with no known plasmid replicons detected by PlasmidFinder. Virulence profiling identified genes associated with flagellar motility, chemotaxis, and stress response, but no distinctive high-virulence profile. Phylogenetic analysis of 43 genomes placed the isolate within a diverse Andean population, revealing that several regional isolates previously classified as S. marcescens belonged to other complex species. These findings emphasize the value of whole-genome sequencing for accurate species identification and genomic surveillance of the S. marcescens complex in resource-limited settings.