In vitro activity of cadazolid against clinically relevant Clostridium difficile isolates and in an in vitro gut model of C. difficile infection

The promotion of colonization with vancomycin-resistant enterococci (VRE) is one potential side effect during treatment of Clostridium difficile-associated diarrhea (CDAD), resulting from disturbances in gut microbiota. Cadazolid (CDZ) is an investigational antibiotic with potent in vitro activity against C. difficile and against VRE and is currently in clinical development for the treatment of CDAD. We report that CDZ treatment did not lead to intestinal VRE overgrowth in mice.C urrent antibiotic treatment of Clostridium difficile-associated diarrhea (CDAD) is mostly done with oral metronidazole (MDZ) and vancomycin (VAN), while only VAN is approved by the FDA. Both drugs promote overgrowth of vancomycin-resistant enterococci (VRE) in the gut and long-term colonization on treatment (1). Recently, the antibiotic fidaxomicin (FDX) was approved by the FDA as a new treatment option for CDAD. Its clinical impact on VRE overgrowth is still unclear. Colonization with VRE represents a major source for VRE bloodstream infections, endocarditis, and urinary tract infections, a particular problem in intensive care units (ICUs) (2-5). Infections caused by VRE are more serious and are associated with a higher mortality rate than those caused by vancomycin-sensitive enterococci (6-9). VRE control appears to be highly challenging. Therefore, preventing VRE colonization represents an important health care goal, particularly in the ICU. FIG 1Mice were pretreated with cadazolid, vancomycin, fidaxomicin, or metronidazole once daily at the indicated doses per kilogram body weight per day (vehicle-treated group, 0 mg/kg) from day Ϫ2 to day ϩ2 and infected with VRE on day 0. Results are expressed as change in log CFU per cecum (versus vehicle group) at 3 days postinfection. Shown are 25% to 75% interquartile range (box), median (intersection), and minimum-maximum (t bar) values for each group. Data were pooled from two similar, independent experiments. API, active pharmacological ingredient. *, P Ͻ 0.05; ***, P Ͻ 0.001. (10), exhibited efficacy and potency in prevention of CDAD similar or superior to VAN, MDZ, and FDX in the mouse model for CDAD (10, 11). CDZ exhibited potent in vitro activity not only against C. difficile clinical isolates but also against VRE (MIC 90 , 2 g/ml) (12, 13), while having a limited impact on bacteria of the normal gut microflora in the in vitro human gut model (14). Recently, a phase 2 trial in CDAD showed clinical cure rates with CDZ treatment similar to those with VAN treatment, while having lower recurrence rates, resulting in higher sustained cure rates (15).In order to investigate the impact of CDZ on intestinal VRE expansion, a mouse model for VRE colonization was employed (1; see Supplementary Material and Methods in the supplemental material). All animal housing and experiments were conducted in agreement with the Swiss Federal Ordinance for animal protection, the animal welfare guidelines from the Cantonal Veterinary Office Basellandschaft, and the Actelion Pharmaceuticals, Ltd., internal anim...

supporting

confidence: 86%

mentioning

confidence: 99%

Cadazolid Does Not Promote Intestinal Colonization of Vancomycin-Resistant Enterococci in Mice

Seiler

Enderlin-Paput

Pfaff

et al. 2016

“…Linezolid is not used to treat C. difficile infection, although the new oxazolidinone cadazolid is being evaluated as a promising therapeutic option to treat C. difficile infection (23,24). Cadazolid has shown very good activity against C. difficile strains (including some linezolid-resistant strains) in an in vitro gut model (23); however, in the studies cited, the molecular mechanisms of resistance to linezolid were not reported.…”

Section: Resultsmentioning

confidence: 99%

Clostridium difficile Isolates with High Linezolid MICs Harbor the Multiresistance Gene cfr

Marı́n

Martín

Alcalá

et al. 2015

We studied the molecular mechanisms of linezolid resistance in 9 isolates of toxigenic Clostridium difficile with high linezolid MICs. The activity of linezolid was determined against 891 clinical isolates of toxigenic C. difficile. The MIC 50 and MIC 90 of linezolid were 0.75 g/ml and 1.5 g/ml, respectively. Nine strains (1%) showed high linezolid MICs (6 g/ml to 16 g/ml) and also were resistant to clindamycin, erythromycin, and chloramphenicol. These strains were selected for molecular studies: sequencing of domain V of the 23 rRNA gene, detection of the cfr methyltransferase gene, and sequencing of the ribosomal protein genes rplC and rplD. Molecular relatedness between strains was assessed using PCR ribotyping and MLVA (multilocus variablenumber tandem-repeat analysis) typing. The strains belonged to ribotypes 001 (2/9), 017 (6/9), and 078 (1/9). MLVA showed that strains of ribotype 001 and 017 belonged to the same clonal complex in each ribotype. We did not detect mutations in the 23S rRNA gene. The cfr gene was detected in 7 of 9 strains. Sequencing of cfr amplicons revealed a similarity of 100% to a fragment of transposon Tn6218 of C. difficile, which was annotated as a putative chloramphenicol/florfenicol resistance protein. We were unable to detect mechanisms of resistance to linezolid in the 2 strains belonging to ribotype 001. While the relevance of our results lies in the detection of the cfr gene as a possible mechanism of resistance to linezolid in C. difficile, our findings should be assessed by further investigations to characterize these possible cfr genes and their contribution to linezolid resistance. Linezolid is the first antibiotic in the oxazolidinone group and has been used for more than 10 years to treat Gram-positive infections (1). Resistance to linezolid in Gram-positive bacteria is very uncommon and has been reported mainly in clinical isolates of coagulase-negative staphylococcus, Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium, as well as in nonhuman isolates of other Gram-positive bacteria and Gram-negative bacteria (2). Resistance is due to the presence of 1 or more of 3 mechanisms: point mutations in the 23S rRNA gene (central loop of domain V, mainly G2576T), mutations/deletions in ribosomal proteins L3 (rplC gene) and L4 (rplD gene), and methylation of position A2503 of the 23S rRNA gene mediated by an rRNA methyltransferase encoded by the multiresistance gene cfr (chloramphenicol-florfenicol resistance), which is harbored mainly in transferable plasmids (3). This last mechanism also has been associated with resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A antibiotics (4).Clostridium difficile is the main cause of antibiotic-associated diarrhea. Although linezolid is not used for the treatment of C. difficile infection (5, 6), some observations suggest that patients treated with linezolid for ventilator-associated pneumonia could be protected against this infection (7).Resistance to linezolid occasionally has bee...

“…It is believed that a narrow-spectrum antibiotic with no or limited effect on members of the normal gut flora, notably the Bacteroides group, is an important factor for sustained treatment success against CDAD with less recurrence, as exemplified clinically for fidaxomicin (28). In an in vitro human gut model using therapeutic doses of cadazolid, the drug had very limited impact on the normal gut microflora, notably sparing the Bacteroides group (17). However, in the end clinical data will be needed to demonstrate the impact of cadazolid on the gut microbiota.…”

Section: Discussionmentioning

confidence: 99%

“…1) currently in clinical development for CDAD. Cadazolid showed potent in vitro activity against C. difficile clinical isolates (15,16) and in a human gut model of CDAD, while having only a very limited impact on bacteria of the normal gut microflora (17). In phase 1 studies, this compound was well tolerated, with a very low systemic exposure resulting in a high concentration in the colon (18).…”

mentioning

confidence: 99%

In VitroandIn VivoAntibacterial Evaluation of Cadazolid, a New Antibiotic for Treatment of Clostridium difficile Infections

Locher

Seiler

Chen

et al. 2014

bClostridium difficile is a leading cause of health care-associated diarrhea with significant morbidity and mortality, and new options for the treatment of C. difficile-associated diarrhea (CDAD) are needed. Cadazolid is a new oxazolidinone-type antibiotic that is currently in clinical development for treatment of CDAD. Here, we report the in vitro and in vivo antibacterial evaluation of cadazolid against C. difficile. Cadazolid showed potent in vitro activity against C. difficile with a MIC range of 0.125 to 0.5 g/ml, including strains resistant to linezolid and fluoroquinolones. In time-kill kinetics experiments, cadazolid showed a bactericidal effect against C. difficile isolates, with >99.9% killing in 24 h, and was more bactericidal than vancomycin. In contrast to metronidazole and vancomycin, cadazolid strongly inhibited de novo toxin A and B formation in stationary-phase cultures of toxigenic C. difficile. Cadazolid also inhibited C. difficile spore formation substantially at growth-inhibitory concentrations. In the hamster and mouse models for CDAD, cadazolid was active, conferring full protection from diarrhea and death with a potency similar to that of vancomycin. These findings support further investigations of cadazolid for the treatment of CDAD.C lostridium difficile infection (CDI), or CDAD for C. difficileassociated diarrhea, is a major health care problem and a leading cause of morbidity and mortality in elderly hospitalized patients (1, 2). During the past decade, there has been a renewed interest in CDAD triggered by an increase in both frequency and severity of the disease in the Western world and the discovery of new hypervirulent strains (3-6), as well as an increased incidence of CDAD in the community (7). CDAD results from overgrowth of toxin-producing strains in the colon, typically following disturbances of the normal protective enteric flora. Clinical symptoms range from asymptomatic colonization to diarrhea, severe pseudomembranous colitis, sepsis, and death. The main virulence factors of C. difficile are two high-molecular-weight toxins, the enterotoxin toxin A (TcdA) and the cytotoxin toxin B (TcdB), while the contribution of the binary toxin remains unclear (8). Toxin A and toxin B cause damage to the intestinal epithelial barrier and promote mucosal inflammation. In fact, the main clinical symptoms of CDAD (secretory diarrhea and inflammation of the colonic mucosa) can be explained by the action of toxins A and B (8). Moreover, C. difficile produces endospores that are resistant to antibiotic treatment and routine disinfection (9). Spores surviving in the gut of patients and in the hospital environment may play a major role in reinfection and relapse of CDAD. Current antibiotic therapy for CDAD includes vancomycin and metronidazole, which have limited treatment success in severe disease, and high recurrence rates of up to 30% have been observed with these treatments (10). Only one new antibiotic, fidaxomicin (11, 12), has been approved in the last 30 years for this indication. In c...