Antimicrobial susceptibility patterns of enterococci in intensive care units in Sweden evaluated by different MIC breakpoint systems

Three hundred and twenty-two (322) clinical isolates were collected from pa tients admitted to intensive care units (ICUs) at eight Swedish hospitals b etween December 1996 and December 1998. Of the isolates, 244 (76%) were Ent erococcus faecalis, 74 (23%) were Enterococcus faecium and four (1%) were o ther Enterococcus spp. MICs of ampicillin, imipenem, meropenem, piperacilli n/tazobactam, ciprofloxacin, trovafloxacin, clinafloxacin, gentamicin, stre ptomycin, vancomycin, teicoplanin, quinupristin/dalfopristin, linezolid and evernimicin were determined by Etest. Susceptible and resistant isolates w ere defined according to the species-related MIC breakpoints of the British Society for Antimicrobial Chemotherapy (BSAC), the National Committee for Clinical Laboratory Standards (NCCLS) and the Swedish Reference Group for A ntibiotics (SRGA). Tentative breakpoints were applied for new/experimental antibiotics. Multidrug resistance among enterococci in ICUs is not uncommon in Sweden, particularly among E. faecium, and includes ampicillin resistan ce and concomitant resistance to fluoroquinolones. Almost 20% of E. faecali s isolates showed high-level resistance to gentamicin and concomitant resis tance to fluoroquinolones. Vancomycin-resistant enterococci were only found sporadically. Among the new antimicrobial agents, linezolid and evernimici n showed the best activity against all enterococcal isolates. There was goo d concordance between the BSAC, NCCLS and SRGA breakpoints in detecting res istance. When applying the SRGA breakpoints for susceptibility, isolates we re more frequently interpreted as intermediate. This might indicate earlier detection of emerging resistance using the SRGA breakpoint when the native population is considered susceptible, but with the risk that isolates belo nging to the native susceptible population will be incorrectly interpreted as intermediate.