Spread of carbapenemase-producing Serratia spp. in France from 2016 to 2024: a comparative genomic study

Carbapenemase-producing Serratia spp. are increasingly implicated in healthcare-associated infections. This study aimed to characterize the genetic diversity, resistance mechanisms, and susceptibility to last resort antimicrobials of carbapenem-resistant Serratia spp. in France. From 2016 to 2024, 193 carbapenemase-producing Serratia spp. from France were investigated. WGS enabled species identification, MLST typing, resistome characterization and phylogenetic analysis. Antimicrobial susceptibility was assessed by broth microdilution, focusing on last resort antimicrobials. Intrinsic resistance to polymyxins was explored by genomic analysis and lipid A mass spectrometry. S. sarumanii (54%) and S. nevei (41%) dominated the epidemiology while no S. marcescens was identified. The most prevalent carbapenemases were OXA-48-like (56%), NDM (25%), IMP (8%), and VIM (7%). MLST identified 67 sequence types (ST) with 42% of the isolates belonging to four high-risk clones: ST-601, ST-298, ST-477, ST-600 and ST-474. β-lactamse susceptibility was low, but aztreonam-avibactam remained highly active (98%). Intrinsic resistance to polymyxin did not result from lipid A modifications as reported for Proteae. In France, carbapenemase-producing Serratia spp. were dominated by S. sarumanii and S. nevei. The absence of S. marcescens, the genus leader, highlighted the need to update the MALDI-TOF database. This study highlights Serratia as an underestimated reservoir of multidrug resistance.