Antimicrobial resistance among Gram-positive agents of bacteraemia in the UK and Ireland: trends from 2001 to 2019

Objectives. The BSAC Bacteraemia Resistance Surveillance collected isolates from UK and Irish hospitals for central testing. Concurrent UKHSA surveillance collated English hospitals’ own susceptibility data. Results were collated and compared.

Methods. BSAC Surveillance collected quotas of isolates per site annually from 2001-19. MIC testing was by BSAC agar dilution, with resistance mechanisms identified by synergy tests, interpretive reading and PCR. The UKHSA sought hospitals’ data on all bacteraemia isolates.

Results. Both surveillance systems recorded dramatic falls in MRSA, from c. 40% of bloodstream Staphylococcus aureus in 2001 to <10% by 2019. Both noted rises in the proportion of MRSA (especially) and MSSA resistant to fusidic acid, along with declines of ciprofloxacin and macrolide resistance amongst MRSA. Methicillin resistance also fell among coagulase-negative staphylococci, albeit only modestly; fusidic acid resistance rose. Shifts for pneumococci were complex reflecting vaccine-contingent serotype displacements; resistance rates remained low, with high-dose penicillin almost universally active. Enterococcus faecium became more prevalent relative to Enterococcus faecalis; vancomycin resistance averaged 29% among E. faecium versus 2% in E. faecalis, without trend. Erythromycin resistance rose among groups B, C and G (but not group A) streptococci. Oxazolidinones, tigecycline, daptomycin and anti-PBP2’ cephalosporins retained near-universal activity against target species, except that tigecycline has been compromised by breakpoint reductions for streptococci.

Conclusions. Gram-positive pathogens were the dominant historical agents of bacteraemia. The trends seen here – with many near-universally active antibiotics – indicate little hazard of this situation returning. Nevertheless, few treatments exist in some settings, notably multiresistant E. faecium endocarditis.