In Vitro Activity of Daptomycin against Enterococcus faecalis under Various Conditions of Growth-Phases, Inoculum and pH. e64218

• Published in: PloS one Vol. 8; no. 5
• Main Authors: Argemi, Xavier, Hansmann, Yves, Christmann, Daniel, Lefebvre, Sophie, Jaulhac, Benoit, Jehl, Francois
• Format: Journal Article
• Language: English
• Published: 01.05.2013
• Subjects: Amoxicillin; Enterococcus faecalis
• DOI: 10.1371/journal.pone.0064218

Enterococcus faecalis (E. faecalis) has become a major leading cause of nosocomial endocarditis. Treatment of such infections remains problematic and new therapeutic options are needed. Nine E. faecalis strains were tested: six obtained from patients presenting endocarditis, one with isolated bacteremia, and two reference strains. Antibiotics included daptomycin, alone or in combination, linezolid, tigecycline, rifampicin, gentamicin, teicoplanin, ceftriaxone and amoxicillin. Time-kill studies included colony counts at 1, 4 and 24 h of incubation. Significant bactericidal activity was defined as a decrease of greater than or equal to 3log10CFU/ml after 24 h of incubation. Antibiotics were tested at a low (106 CFU/ml) and high (109 CFU/ml) inoculum, against exponential- and stationary-phase bacteria. We also performed time kill studies of chemically growth arrested E. faecalis. Various pH conditions were used during the tests. In exponential growth phase and with a low inoculum, daptomycin alone at 60 mu g/ml and the combination amoxicillin-gentamicin both achieved a 4-log10 reduction in one hour on all strains. In exponential growth phase with a high inoculum, daptomycin alone was bactericidal at a concentration of 120 mu g/ml. All the combinations tested with this drug were indifferent. In stationary phase with a high inoculum daptomycin remained bactericidal but exhibited a pH dependent activity and slower kill rates. All combinations that did not include daptomycin were not bactericidal in conditions of high inoculum, whatever the growth phase. The results indicate that daptomycin is the only antibiotic that may be able of overcoming the effects of growth phase and high inoculum.