Replacement of Enterococcus faecalis by Enterococcus faecium as the predominant enterococcus in UK bacteraemias

Abstract

Objectives: To review temporal changes in the proportions of different Enterococcus species recorded in two UK bacteraemia surveillance systems. Antibiotic resistance trends were also considered.

Methods: We reviewed data for enterococci from 2001 to 2019 in: (a) the BSAC Resistance Surveillance Programme, which collected up to 7-10 bloodstream enterococci every year from each of 23-39 hospitals in the UK and Ireland and tested these centrally; and (b) PHE bacteraemia surveillance, using routine results from NHS microbiology laboratories in England.

Results: BSAC surveillance, based upon 206-255 enterococci each year (4486 in total), indicated that the proportion of Enterococcus faecium rose from 31% (212/692) in the period 2001-3 to 51% (354/696) in the period 2017-19, balanced by corresponding falls in the proportion of Enterococcus faecalis. PHE surveillance provided a larger dataset, with >5000 enterococcus reports per year; although its identifications are less precise, it too indicated a rise in the proportion of E. faecium. BSAC surveillance for E. faecium indicated no consistent trends in resistance to ampicillin (≥86% in all years), vancomycin (annual rates 19%-40%) or high-level resistance to gentamicin (31%-59%). Resistance to vancomycin remained <4% in E. faecalis in all years, whilst high-level resistance to gentamicin fell, perhaps partly reflecting the decline of two initially prevalent gentamicin- and ciprofloxacin-resistant clones.

Conclusions: Both surveillance systems indicate a growing proportion of E. faecium in enterococcal bloodstream infections. This is important because fewer therapeutic options remain against this frequently multiresistant species than against E. faecalis.

Figure 1.

(a) Distribution of enterococci causing bloodstream infection in the UK and Ireland, 2001–19 (BSAC data). (b) Distribution of enterococci causing bloodstream infection, 2001–19, based on reported identification or proxy identification using ampicillin/amoxicillin resistance (PHE data). Key: Other enterococcus, isolates identified as an enterococcal species other than E. faecalis or E. faecium; Enterococcus genus ID only, isolates identified to Enterococcus genus level only; Ampicillin resistant, enterococci identified as resistant to ampicillin; Ampicillin/amoxicillin resistant, enterococci identified as resistant to ampicillin and/or amoxicillin among those enterococci that were tested against either of these agents.

Figure 2.

Ampicillin, vancomycin, and high-level (HL) gentamicin resistance in Enterococcus faecium (a) and Enterococcus faecalis (b) from bloodstream infection, 2001–19 (BSAC data): 3 year weighted average. Averages are shown at the middle of each 3 year period, so are not available for the first and last years of the data series. High-level resistance to gentamicin is defined as MIC >128 mg/L.

Figure 3.

High-level resistance to gentamicin and ciprofloxacin in Enterococcus faecium (a) and Enterococcus faecalis (b) from bloodstream infection, 2001–19 (BSAC data): 3 year weighted averages. Ciprofloxacin was last tested in 2015. Averages are shown at the middle of each 3 year period, so are not available for the first and last years of the data series. High-level resistance to gentamicin is defined as MIC >128 mg/L; high-level resistance to ciprofloxacin is defined as MIC >16 mg/L.