Dalbavancin And Selected Comparison Agents Tested Against Indicated Gram-Positive Isolates In European Medical Centers (Italy): Results From The Decide Program

Background: Dalbavancin activity was tested against isolates from three medical centers in Italy between October – December, 2007. Only reference quality and standardized CLSI methods were used. Methods: Susceptibility methods for agar diffusion were applied by each investigator: Etest (ET; AB BIODISK) and CLSI disk diffusion (DD) tests performed with concurrent QC with repeated testing of strains showing unusual resistance patterns such as linezolid, teicoplanin or dalbavancin-non-susceptibility (MIC, >0.25 mg/L). 225 strains were tested against dalbavancin and teicoplanin by ET and linezolid, cefoxitin, levofloxacin, gentamicin, tetracycline, erythromycin, clindamycin (plus D-test), penicillin and ceftriaxone by DD. Dalbavancin susceptibility was defined at ≤0.25 mg/L. Results: Dalbavancin showed high activity against the 151 S. aureus (SA; MIC range, ≤0.016–0.25 mg/L), CoNS (≤0.016–0.25 mg/L) and β-haemolytic streptococci (BHS; ≤0.016–0.094 mg/L). This activity was 4-, 16- and ≥4-fold greater than teicoplanin when comparing MIC90 values, respectively. Susceptibility rates among SA were: linezolid (97%), levofloxacin (61%), erythromycin (43%), clindamycin (51%), tetracycline (86%) and gentamicin (70%). Six linezolid-non-susceptible strains were noted among SA and BHS but all had zone diameters (19–20 mm) near the breakpoint (≥21 mm). Teicoplanin-resistant CoNS and levofloxacin-resistant BHS were detected. A distinct trend toward higher dalbavancin ET MIC results was observed, a probable technical reading error also noted for false-resistant DD linezolid results for SA and BHS (six occurrences). D-test inducible-resistant rates for clindamycin varied from 38 (BHS) to 78% (SA). Conclusions: Dalbavancin, a new long-acting glycolipopeptide (once weekly dosing), demonstrated high activity (MIC50 ranges, ≤0.016–0.19 mg/L) against staphylococci and BHS from Italy. The recorded MIC90 was 0.125 mg/L, a confirmed finding suggesting a high MIC reading bias for ET. The most elevated MIC results were at 0.25 mg/L (breakpoint; 33 occurrences among SA). The exhibited dalbavancin potency (4-fold greater than teicoplanin; only tested in Italy DECIDE sample) covered all contemporary Gram-positive pathogens.