Molecular Characterization of Vancomycin-Resistant Enterococci Repopulating the Gastrointestinal Tract following Treatment with a Novel Glycolipodepsipeptide, Ramoplanin

Abstract

We characterized baseline and repopulating stool isolates recovered during a phase II trial of ramoplanin for the treatment of patients with stool carriage of vancomycin-resistant enterococci (VRE). Repopulation with a strain with a related genotype was found in 74, 60, and 53% of individuals in groups treated with placebo, 100 mg of ramoplanin, and 400 mg of ramoplanin, respectively. All ramoplanin-treated patients with a culture positive for VRE at day 7 had a relapse caused by a genotypically related isolate. In ramoplanin-treated patients, antibiotics with activities against anaerobic organisms were associated with positive cultures on day 7 (relative risk [RR] ‫؍‬ 8.8; P ‫؍‬ 0.004), and the avoidance of such antibiotics was significantly associated with culture negativity through day 21 (RR ‫؍‬ 0.16; P ‫؍‬ 0.02).Vancomycin-resistant enterococci (VRE) have dramatically increased in clinical importance over the past decade (10,16,17), with few therapeutic options remaining (5, 16). Strains of VRE causing bacteremia in severely ill patients often originate at sites of colonization in the gastrointestinal tract (2). One strategy for the prevention of infection with VRE in at-risk, colonized patients is suppression of intestinal VRE during the periods of greatest risk. No agent has been demonstrated to have efficacy for this purpose, despite the study of several candidates (novobiocin, doxycycline, bacitracin) (14,15,18,28). Ramoplanin, a glycolipodepsipeptide antimicrobial that is not systemically absorbed, has been demonstrated to have activity against VRE and has been studied as a locally active agent for the suppression of colonization (11,13,21).In a multicenter, randomized, double-blind, placebo-controlled phase II trial, ramoplanin was shown to be safe and effective at suppressing VRE to undetectable levels (at day 7) in 80 to 90% of treated patients (29). Patients colonized with VRE but without evidence of active infection were randomized to receive placebo or ramoplanin at 100 or 400 mg orally twice a day for 7 days. Stool or rectal swab specimens for culture were obtained at the baseline and then at days 7 (end of treatment), 14, 21, 45, and 90. Overall antimicrobial use and use of antimicrobials with activities against anaerobic organisms during the study period were not found to be different between the three treatment groups in relation to their VREfree status. The details of the clinical results from this phase II study have been published elsewhere (29). The purpose of the present study was to assess the molecular relatedness of paired isolates from patients whose colonization with VRE recurred after treatment with ramoplanin.(These data were presented in part at the 1st International American Society for Microbiology Conference of Enterococci, Banff, Alberta, Canada, 2000.) MATERIALS AND METHODSRectal swab specimens were obtained and directly inoculated into 1.0 ml of bile-esculin azide broth with 6 g of vancomycin (Hardy Diagnostics, Santa Maria, Calif.) per ml, as presented elsewhere (29). The ...

Efficacy of Oral Ramoplanin for Inhibition of Intestinal Colonization by Vancomycin-Resistant Enterococci in Mice

“…In our study, a higher dose of ramoplanin (500 g/ml of drinking water) was associated with recurrent colonization in only 50% of treated mice. This observation is consistent with the clinical data that suggest that ramoplanin treatment may result in eradication of VRE in some patients (1).…”

“…Minor disruption of the indigenous microflora by ramoplanin could therefore potentially facilitate reexpansion of VRE that are already present, while being insufficient to allow overgrowth of newly introduced strains. As noted previously, antianaerobic antibiotics that are used concurrently with ramoplanin may facilitate acquisition of new VRE strains after decolonization (1,5).…”

“…Such recurrences may be due to reexpansion of small numbers of VRE that persist in the intestinal tract during treatment or reacquisition of VRE after treatment has eliminated the original colonizing strain or strains. Baden et al (1) found that recurrences after ramoplanin treatment were often associated with isolation of VRE strains that were genotypically unrelated to pretreatment strains, suggesting that new VRE strains might have been acquired. The concurrent use of antianaerobic antibiotics by many of the study patients was a potential confounding variable because these agents have been shown to facilitate overgrowth of preexisting or newly acquired VRE strains (1,5).…”

“…Baden et al (1) found that recurrences after ramoplanin treatment were often associated with isolation of VRE strains that were genotypically unrelated to pretreatment strains, suggesting that new VRE strains might have been acquired. The concurrent use of antianaerobic antibiotics by many of the study patients was a potential confounding variable because these agents have been shown to facilitate overgrowth of preexisting or newly acquired VRE strains (1,5). Similarly, the 100% recurrence rate of VRE colonization observed in a previous mouse study could have been due in part to the fact that oral vancomycin or streptomycin treatment was continued during and after discontinuation of oral ramoplanin (18).…”

Emergence of Multi-Drug Resistance Gram-Positive Bacteria and New Active Antibiotics

“…Ramoplanin, a glycolipodepsipeptide antibiotic that inhibits peptidoglycan synthesis by interrupting late-stage membrane-associated glycosyltransferase reactions catalyzed by the transglycosylase and MurG enzymes [227], is currently being developed as an oral, non-absorbable agent for the prevention of vancomycin-resistant Enterococcus (VRE) infection in patients with VRE gastrointestinal colonization [228,229,230]. Ramoplanin had an excellent in vitro bactericidal activity against a broad range of Gram-positive bacteria including resistant strains [231].…”