The global population structure and beta-lactamase repertoire of the opportunistic pathogen Serratia marcescens

Serratia marcescens is a global spread nosocomial pathogen. This rod-shaped bacterium displays a broad host range and worldwide geographical distribution. Here we analyze an international collection of this multidrugresistant, opportunistic pathogen from 35 countries to infer its population structure. We show that S. marcescens comprises 12 lineages; Sm1, Sm4, and Sm10 harbor 78.3% of the known environmental strains. Sm5, Sm6, and Sm7 comprise only human-associated strains which harbor smallest pangenomes, genomic fluidity and lowest levels of core recombination, indicating niche specialization. Sm7 and Sm9 lineages exhibit the most concerning resistome; blaKPC-2 plasmid is widespread in Sm7, whereas Sm9, also an anthropogenicexclusive lineage, presents highest plasmid/lineage size ratio and plasmid-diversity encoding metallo-betalactamases comprising blaNDM-1. The heterogeneity of resistance patterns of S. marcescens lineages elucidated herein highlights the relevance of surveillance programs, using whole-genome sequencing, to provide insights into the molecular epidemiology of carbapenemase producing strains of this species.

Automated summary

Research has revealed that Serratia marcescens can be classified into 12 lineages, with some containing a large number of environmental strains while others exclusively harbor human-associated strains with specific ecological niches. The diversity of resistant genomes in different lineages underscores the importance of surveillance programs, with whole-genome sequencing providing insights into carbapenemase-producing strains of this species.