Virulence genes in Enterococcus faecium and Enterococcus faecalis isolated from blood culture in haematological patients

Abstract

Objective. To study virulence genes in E. faecium and E. faecalis isolated from the blood cultures of patients with hematological diseases. Materials and Methods. Virulence genes were studied in E. faecium and E. faecalis strains isolated from blood culture from hematological patients in four Russian hospitals (2002–2020). Susceptibility to vancomycin was determined by broth microdilution method (CLSI, 2022). Virulence genes (esp, hyl, asa1, cylA and gelE) in E. faecium and E. faecalis as well as vancomycin resistance genes (vanA, vanB and vanD) in Enterococcus spp. were detected by multiplex PCR. Results. A total of 551 Enterococcus spp. strains were studied, of them 440 (79.9%) were E. faecium and 111 (20.1%) E. faecalis. Resistance to vancomycin was detected in 86 (19.5%) E. faecium, of them 62 (72.1%) carried vanA and 24 (27.9%) vanB genes. One (1.1%) of 111 E. faecalis was vancomycinintermediate (MIC 16 μg/ml) with vanD gene. Virulence genes were detected in 86.2% of Enterococcus spp., significantly more often among E. faecalis (95.5%) compared to E. faecium (83.9%, p = 0.003). The predominant genes in E. faecium were esp (70.2%) and hyl (52.1%), the detection of the asa1, cylA and gelE genes was minimal. Other genes dominated in E. faecalis: gelE (66.7%), asa1 (65.8%), cylA (36.9%). Statistically significant differences between E. faecium and E. faecalis were determined for all studied virulence genes (p < 0.0001). A combination of three or more virulence genes was detected significantly more often among E. faecalis in comparison with E. faecium (45% vs. 2.5%, p < 0.0001), whereas the presence of one gene or their absence prevailed in E. faecium (40.2% vs. 17.1%, p < 0.0001; 16.1% vs. 4.5%, p = 0.003, respectively). When comparing the two study periods (2002–2010 and 2011–2020), E. faecalis showed a significant increase in the proportion of strains with a combination of three or more virulence genes from 33.3% to 55% (p = 0.03), in E. faecium – with one virulence gene (from 31.7% to 46.3%, p = 0.002) and no genes (from 6.6% to 23%, p < 0.0001). Conclusions. Differences in the frequency of detection of virulence genes and their spectrum have been identified between E. faecium and E. faecalis strains. Virulence genes are significantly more often detected in E. faecalis with a predominance of combinations of three or more genes.

Keywords

• enterococcus faecium
• enterococcus faecalis
• virulence