In Vitro Activity of Ramoplanin against Clostridium difficile , Including Strains with Reduced Susceptibility to Vancomycin or with Resistance to Metronidazole

Abstract

We evaluated the in vitro activity of ramoplanin, an antimicrobial compound that inhibits cell wall synthesis by acting at the level of lipid intermediate formation, against Clostridium difficile. We included strains with reduced susceptibilities to vancomycin (vancomycin-intermediate [Van i ] strains) or with resistance to metronidazole (Mtz r ), in order to assess the potential utility of ramoplanin for the treatment of C. difficile-associated diarrhea. We tested the activity of ramoplanin against a total of 105 nonduplicate clinical isolates of toxigenic C. difficile, including 8 Van i isolates and 6 Mtz r isolates, obtained from our laboratory. Ramoplanin was active against all strains tested at concentrations ranging from 0.03 to 0.5 g/ml (MICs at which 50 and 90% of isolates were inhibited, 0.25 g/ml; geometric mean MIC, 0.22 g/ml). All isolates, independently of their levels of susceptibility to vancomycin or metronidazole, were considered susceptible to ramoplanin (MICs, <0.5 g/ml).Rates of Clostridium difficile-associated diarrhea (CDAD) are increasing in hospitals worldwide as a consequence of the widespread use of broad-spectrum antibiotics, and the organism may also be an important cause of community-acquired diarrhea (1,9,14,17). The drugs of choice for the treatment of CDAD are metronidazole (MTZ) and oral vancomycin (VAN).Our group recently reported on the isolation of MTZ-resistant (Mtz r ) and VAN-intermediate (Van i ) C. difficile strains (19). The roles of these nonsusceptible strains in clinical failures and relapses remain unknown, but therapeutic alternatives must be sought.Ramoplanin, a lipoglycodepsipeptide antibiotic obtained from the fermentation of an Actinoplanes strain (ATCC 33076), is being developed as an oral, nonabsorbable agent for the gastrointestinal decontamination of patients infected or colonized with 15,24). No cross-resistance between ramoplanin and VAN has been so far described, due to differences in their structures and mechanisms of action (6, 21).Our objective was to evaluate the in vitro activity of ramoplanin against C. difficile, with a special interest in those strains that have reduced susceptibilities to VAN MATERIALS AND METHODSThe activity of ramoplanin was tested against a total of 105 nonduplicate clinical isolates of toxigenic C. difficile obtained in our laboratory over a 9-year period (1994 to 2002). Eight of the strains had reduced susceptibility to VAN, and six strains were MTZ resistant. The MICs of VAN for the C. difficile Van i isolates were 4 g/ml (six strains) and 8 g/ml (two strains); and the MTZ MICs for the Mtz r isolates were 16 g/ml (three strains), 32 g/ml (two strains), and 64 g/ml (one strain).C. difficile isolates were presumptively identified by their colony morphology, yellow color, ground-glass texture, and characteristic horse dung smell and by Gram staining (16). Additional biochemical tests (Rapid ID 32A system; bio Mérieux, Marcy l'Etoile, France) were also used. All the strains with reduced susceptibilities to VAN and resist...

Ambush of Clostridium difficile Spores by Ramoplanin: Activity in an In Vitro Model

“…Ramoplanin has known bactericidal activities against wild-type C. difficile and strains with reduced susceptibilities to vancomycin and has been studied in an open-label phase 2 clinical trial evaluating early clinical efficacy (12,13). Ramoplanin was also previously reported to have activity against C. difficile spores in an in vitro gut model and an in vivo hamster model (14).…”

Antimicrobial Susceptibility Pattern of Clostridium difficile and Its Relation to PCR Ribotypes in a Swedish University Hospital

“…However, resistance to metronidazole in up to 9% of isolates (1,4,6,18), intermediate resistance to vancomycin in 3% of isolates (1), and "relatively poor" outcome of metronidazole therapy in CDAD (15,19,28) was recently reported. This emphasizes the need for periodic monitoring of any emergence of drug resistance in C. difficile.…”

Clinical update for the diagnosis and treatment ofClostridium difficileinfection

“…In the same study mentioned above, all isolates of C. difficile were sensitive to ramoplanin with an MIC 90 of 0.5 μg/mL [204] . In another study, which included C. difficile isolates with reduced susceptibility to vancomycin and resistance to metronidazole, no resistance was found to ramoplanin [205] . In a hamster model of CDI, both ramoplanin and vancomycin were uniformly effective in resolution of symptoms [96] .…”