Distribution of virulence genes in vancomycin-resistant Enterococcus faecium (VREfm) from bloodstream infections in North Rhine-Westphalia

Question

Vancomycin-resistant Enterococcus faecium (VREfm) is a multidrug-resistant pathogen that can cause severe nosocomial infections including bloodstream infections. In recent years, there has been a significant increase in the incidence of multilocus sequence type (MLST ST) 117 in Germany. As the genomic content with accessory genes is highly variable, we hypothesize that the comprehensive equipment with virulence genes might be responsible for the successful spread of ST117. The aim of this study was to analyze the distribution of 32 known virulence genes in VREfm from bloodstream infections.

Methods

From October 2015 to May 2023, 187 VREfm isolates from bloodstream infections isolated in microbiology laboratories in the German federal state of North Rhine-Westphalia were included into the study. After whole genome sequencing (WGS), the MLST ST and core genome MLST (cgMLST) cluster types (CT) were extracted. In total, the sequences were examined for the presence of 32 virulence genes coding for known virulence factors of VREfm.

Results

The isolates in the study cohort had the MLST ST117 (n=50), ST80 (n=50), ST17 (n=8), ST192 (n=25), ST612 (n=7), ST1299 (n=6) and ST203 (n=41). The distribution of virulence genes in the investigated MLST sequence types were found to be distinctly variable for several virulence genes that code for adhesion factors, biofilm formation, survival and capsule formation, i.e. scm, esp, hyl, ecbA, pilA, lwpC, swpC, fms15, tirE1/tirE2 and capD. Interestingly, the presence of these virulence genes was relatively stable for isolates with certain MLST STs and cgMLST CTs. Isolates with the same cgMLST CT therefore usually had the same set of virulence genes. ST117 exhibited the broadest spectrum of virulence genes and particularly higher prevalence of ecbA, hyl, capD and tirE1/tirE2 compared to the other MLST STs.

Conclusions

The distribution of virulence genes in VREfm is variable, but relatively stable for certain MLST ST and particularly cgMLST CT as surrogates for the genomic background. ST117 had the most extensive set of virulence genes, which might be a key factor for the successful distribution of ST117 in Germany.