The isolates were collected mainly from bloodstream infection (55.1%), skin and skin structure infections (22.3%) and pneumonia (8.1%). France (940 strains; 20.3% of all isolates), Germany (848 strains; 18.3%) and Italy (519 strains; 11.2%) contributed with the highest number of strains; while Greece (78 strains; 1.7%), Israel (187 strains; 4.0%) and Switzerland (217 strains; 4.7%) supplied the lowest number of samples (Table ). The frequencies of oxacillin resistance among staphylococci and vancomycin resistance among enterococci by country are listed in Table , and showed that oxacillin resistance rates varied from 2.1% in Sweden (187 strains) to 42.5% in the United Kingdom (UK; 153 strains) and 54.7% in Ireland (203 strains) among S. aureus (29.1% overall). Oxacillin resistance rates were most elevated among CoNS strains, varying from 53.3% in the UK (30 strains) to 83.3% in Greece (24 strains). Vancomycin-resistant E. faecalis strains were detected only in Italy (one strain; 1.6%) and UK (five strains; 17.9%), while among E. faecium, the vancomycin resistance rates varied from 0.0% in France, Sweden and Switzerland to 66.7% in the UK (18 strains) and 71.4% in Ireland (14 strains), with an all Europe rate of 17.9% (Table ).
Number of strains tested from European nations in the 2005 surveillance sample.
Frequency of important resistance phenotypes by European nation.
Daptomycin was generally very potent against the Gram-positive organisms collected in European medical centers in 2005 (Table ). All S. aureus strains were inhibited at a daptomycin MIC of ≤1 mg/L (100.0% susceptible) with a MIC50 of 0.25 mg/L and a MIC90 of only 0.5 mg/L. A slight trend toward higher daptomycin MIC values was observed for MRSA (52.8% at 0.25 mg/L and 43.8% at 0.5 mg/L) compared to oxacillin (methicillin)-susceptible S. aureus (MSSA; 70.7% at 0.25 mg/L and 24.9% at 0.5 mg/L). This very modest skewing was less apparent for CoNS where the frequency of strains inhibited at 0.25 mg/L were 48.1 and 47.3%, and at 0.5 mg/L were 33.6 and 43.2% for oxacillin (methicillin)-susceptible (MS-CoNS) and oxacillin (methicillin)-resistant (MR-CoNS) strains, respectively. Only one CoNS strain (0.1%) exhibited an elevated daptomycin MIC value for an oxacillin-susceptible strain isolated from a medical center located in Rome, Italy (reproducible MIC value of 4 mg/L). All other CoNS strains were inhibited at daptomycin MIC ≤1 mg/L (Table ).
Frequency of occurrence of daptomycin MIC values for key Gram-positive pathogens.
Daptomycin was also highly active against enterococci (Table ). Among 646 tested E. faecalis (MIC50, 0.5 mg/L; MIC90, 1 mg/L; 100% susceptible) the highest daptomycin MIC value was only 2 mg/L (2.2% of strains tested); while among E. faecium (MIC50, 2 mg/L; MIC90, 4 mg/L; 100% susceptible) the highest MIC value was 4 mg/L.
MSSA strains showed high rates of susceptibility (>95%) to most comparison antimicrobial agents tested except erythromycin (85.9% susceptibility), ciprofloxacin (93.0%) and levofloxacin (93.9%). In contrast, resistance rates to many agents were high among MRSA strains (Table ). The most active compounds tested against this pathogen (100.0% susceptible) were daptomycin (MIC90, 0.5 mg/L), linezolid (MIC90, 2 mg/L), teicoplanin (MIC90, ≤2 mg/L) and vancomycin (MIC90, 1 mg/L; Table ). CoNS showed higher rates of resistance compared to S. aureus. The fluoroquinolones, ciprofloxacin and levofloxacin, were active against only 86.9 and 87.3% of MS-CoNS, respectively. In contrast, daptomycin, linezolid and vancomycin were the only compounds active against 100.0% of MR-CoNS at the susceptible breakpoint (Table ). It is important to note the emergence of quinupristin/dalfopristin resistance among both MRSA (98.6% susceptible) and MR-CoNS (99.3% susceptible).
Antimicrobial activity of daptomycin and selected comparators tested against European S. aureus and enterococcal isolates (2005).
Daptomycin (MIC90, 0.5 mg/L; 100.0% susceptible), ampicillin (MIC90, 2 mg/L; 99.4% susceptible) and linezolid (MIC90, 2 mg/L; 100.0% susceptible) were very active against E. faecalis, and only six vancomycin-resistant E. faecalis strains (0.9%) were detected in Europe in 2005 (Table ). These strains were from Italy (one strains) and the UK (five strains), and all six strains showed low daptomycin MIC values (0.25 – 1 mg/L). On the other hand, E. faecium exhibited high rates of resistance to most antimicrobials tested. Resistance to vancomycin was observed in 17.9% of E. faecium strains (Table ) and only daptomycin (MIC50, 2 mg/L and MIC90, 4 mg/L) and linezolid (MIC50, 1 mg/L and MIC90, 2 mg/L) were active against all vancomycin-resistant E. faecium strains tested. Furthermore, only 72.7% of vancomycin-resistant and 70.2% of vancomycin-susceptible E. faecium strains were susceptible to quinupristin/dalfopristin (Table ).