Tracing the possible evolutionary trends of Morganella morganii : insights from molecular epidemiology and phylogenetic analysis.

Morganella morganii , encompassing two subspecies, subsp. morganii and subsp. sibonii , is a common opportunistic pathogen, notable for intrinsic resistance to multiple antimicrobial agents. Despite its clinical significance, research into the potential evolutionary dynamics of M. morganii remains limited. This study involved the analysis of genome sequences from 431 M . morganii isolates, comprising 206 isolates that cause host infections, obtained from this study and 225 from the NCBI genome data sets. A diverse array of antimicrobial resistance genes (ARGs) was identified in M. morganii isolates, including mcr-1 , tet (X4), tmexCD-toprJ , and various carbapenemase genes. In addition, a novel bla KPC-2 -bearing plasmid with demonstrated conjugative capability was discovered in M. morganii . The majority of virulence-related genes (VRGs), except for the hlyCABD gene cluster, were found in almost all M. morganii . Three novel genospecies of M. morganii were identified, designated as M. chanii , M. variant1 , and M. variant2 . Compared to M. sibonii , M. chanii genospecies possessed a greater number of flagellar-related genes, typically located within mobile genetic elements (MGEs), suggesting potential for better environmental adaptability. Phylogenetic analysis further disclosed that M. morganii was divided into 12 sequence clusters (SCs). Particularly, SC9 harbored an elevated abundance of ARGs and VRGs, mainly toxin-related genes, and was associated with a higher presence of MGEs compared to non-SC9 strains. The collective findings suggest that M. morganii undergoes evolution driven by the influence of MGEs, thereby significantly enhancing its adaptability to selective pressures of environmental changes and clinical antimicrobial agents.IMPORTANCEThe growing clinical significance of Morganella morganii arises from its abundant virulence factors and antimicrobial resistance genes, resulting in elevated infection rates and increased clinical scrutiny. However, research on the molecular epidemiology and evolutionary trends of M. morganii has been scarce. Our study established a list of virulence-related genes (VRGs) for M. morganii and conducted a large-scale epidemiological investigation into these VRGs. Based on genomic classification, three novel genotypes of M. morganii were identified, representing evolutionary adaptations and responses to environmental challenges. Furthermore, we discovered the emergence of a sequence cluster enriched with antimicrobial resistance genes, VRGs, and mobile genetic elements, attributed to the selective pressure of antimicrobial agents. In addition, we identified a novel conjugative plasmid harboring the bla KPC-2 gene. These findings hold significance in monitoring and comprehending the epidemiology of M. morganii .