Activities of Fosfomycin and Rifampin on Planktonic and Adherent Enterococcus faecalis Strains in an Experimental Foreign-Body Infection Model

• DOI: 10.1128/aac.02583-12
• Publication Date: 2013-10-22T02:41:14Z
• Authors: Alessandra Oliva; Ulrika Furustrand...; Elena Maryka Maiolo; Safaa Jeddari; Bertrand Bétrisey; Andrej Trampuz
• Keywords: Male; 0301 basic medicine; Guinea Pigs; Microbial Sensitivity Tests; Calorimetry; Bacterial Adhesion; 03 medical and health sciences; Daptomycin; Fosfomycin; Acetamides; Enterococcus faecalis; Animals; Gram-Positive Bacterial Infections; Oxazolidinones; Linezolid; Foreign Bodies; acetamides; ampicillin; animals; anti-bacterial agents; bacterial adhesion; biofilms; calorimetry; daptomycin; disease models; animal; drug therapy; combination; enterococcus faecalis; foreign bodies; fosfomycin; gentamicins; gram-positive bacterial infections; guinea pigs; linezolid; male; microbial sensitivity tests; oxazolidinones; rifampin; vancomycin; Anti-Bacterial Agents; 3. Good health; Disease Models, Animal; Biofilms; Ampicillin; Drug Therapy, Combination; Gentamicins

ABSTRACT

Enterococcal implant-associated infections are difficult to treat because antibiotics generally lack activity against enterococcal biofilms. We investigated fosfomycin, rifampin, and their combinations against planktonic and adherent Enterococcus faecalis (ATCC 19433) in vitro and in a foreign-body infection model. The MIC/MBC log values were 32/>512 μg/ml for fosfomycin, 4/>64 μg/ml for rifampin, 1/2 μg/ml for ampicillin, 2/>256 μg/ml for linezolid, 16/32 μg/ml for gentamicin, 1/>64 μg/ml for vancomycin, and 1/5 μg/ml for daptomycin. In time-kill studies, fosfomycin was bactericidal at 8× and 16× MIC, but regrowth of resistant strains occurred after 24 h. With the exception of gentamicin, no complete inhibition of growth-related heat production was observed with other antimicrobials on early (3 h) or mature (24 h) biofilms. In the animal model, fosfomycin alone or in combination with daptomycin reduced planktonic counts by ≈4 log 10 CFU/ml below the levels before treatment. Fosfomycin cleared planktonic bacteria from 74% of cage fluids (i.e., no growth in aspirated fluid) and eradicated biofilm bacteria from 43% of cages (i.e., no growth from removed cages). In combination with gentamicin, fosfomycin cleared 77% and cured 58% of cages; in combination with vancomycin, fosfomycin cleared 33% and cured 18% of cages; in combination with daptomycin, fosfomycin cleared 75% and cured 17% of cages. Rifampin showed no activity on planktonic or adherent E. faecalis , whereas in combination with daptomycin it cured 17% and with fosfomycin it cured 25% of cages. Emergence of fosfomycin resistance was not observed in vivo . In conclusion, fosfomycin showed activity against planktonic and adherent E. faecalis . Its role against enterococcal biofilms should be further investigated, especially in combination with rifampin and/or daptomycin treatment.