Susceptibility of gram-positive cocci from 25 UK hospitals to antimicrobial agents including linezolid. The Linezolid Study Group.
Henwood CJ., Livermore DM., Johnson AP., James D., Warner M., Gardiner A.
The prevalence of antibiotic resistance amongst Gram-positive cocci from 25 UK hospitals was studied over an 8 month period in 1999. A total of 3770 isolates were tested by the sentinel laboratories using the Etest; these bacteria comprised 1000 pneumococci, 1005 Staphylococcus aureus, 769 coagulase-negative staphylococci (CNS) and 996 enterococci. To ensure quality, 10% of the isolates were retested centrally, as were any found to express unusual resistance patterns. The prevalence of penicillin-resistant Streptococcus pneumoniae, vancomycin-resistant enterococci and methicillin-resistant S. aureus (MRSA) varied widely amongst the sentinel laboratories. The resistance rates to methicillin among S. aureus and CNS were 19.2 and 38.9%, respectively, with MRSA rates in individual sentinel sites ranging from 0 to 43%. No glycopeptide resistance was seen in S. aureus, but 6.5% of CNS isolates were teicoplanin resistant and 0.5% were vancomycin resistant. Vancomycin resistance was much more frequent among Enterococcus faecium (24.1%) than E. faecalis (0.5%) (P<0.05), with most resistant isolates carrying vanA. The rate of penicillin resistance in pneumococci was 8.9%, and this resistance was predominantly intermediate (7.9%), with only six hospitals reporting isolates with high level resistance. The prevalence of erythromycin resistance among pneumococci was 12.3%, with the majority of resistant isolates having the macrolide efflux mechanism mediated by mefE. All the organisms tested were susceptible to linezolid with MICs in the range 0.12-4 mg/L. The modal MICs of linezolid were 1 mg/L for CNS and pneumococci, and 2 mg/L for S. aureus and enterococci. Linezolid was the most potent agent tested against Gram-positive cocci, including multiresistant strains, and as such may prove a valuable therapeutic option for the management of Gram-positive infections in hospitals.