In vitro Activity of Rifaximin, Metronidazole and Vancomycin against Clostridium difficile and the Rate of Selection of Spontaneously Resistant Mutants against Representative Anaerobic and Aerobic Bacteria, Including Ammonia-Producing Species

• Published in: Chemotherapy (Basel) Vol. 46; no. 4; pp. 253 - 266
• Main Authors: Marchese, Anna, Salerno, Angelo, Pesce, Adelaide, Debbia, Eugenio A., Schito, Gian Carlo
• Format: Journal Article
• Language: English
• Published: Basel, Switzerland Karger 01.07.2000; S. Karger AG
• Subjects: Ammonia - metabolism; Anti-Bacterial Agents - pharmacology; Antibacterial agents; Antibiotics. Antiinfectious agents. Antiparasitic agents; Bacteria, Aerobic - drug effects; Bacteria, Anaerobic - drug effects; Bacteroides; Biological and medical sciences; Citrobacter freundii; Clostridium; Clostridium difficile; Clostridium difficile - drug effects; Clostridium difficile - metabolism; Drug Resistance, Microbial - genetics; Escherichia coli; Fusobacterium nucleatum; Gastrointestinal Agents - pharmacology; Humans; Medical sciences; Metronidazole - pharmacology; Microbial Sensitivity Tests; Microbiology; Pharmacology. Drug treatments; Proteus; Providencia rettgeri; Rifamycins - pharmacology; Salmonella enteritidis; Selection, Genetic; Vancomycin - pharmacology; Rifaximin; Spontaneous resistance; Clostridium difficile; Nitro compound; Imidazole derivatives; Peptides; Clostridiales; Vancomycin; In vitro; Antibiotic; Sensitivity resistance; Glycopeptide; Clostridiaceae; Bacteria; Metronidazole; Antibacterial agent; Clinical isolate; Comparative study
• ISSN: 0009-3157; 1421-9794
• DOI: 10.1159/000007297

Background: Rifaximin is a rifamycin derivative characterized by a wide antibacterial activity. This drug is neither absorbed by the gastrointestinal tract nor inactivated by gastric juices, and exerts its action entirely within the intestinal lumen. Methods: In this study, the activity of this antibiotic was compared with that of metronidazole and vancomycin against 93 Clostridium difficile isolates. The rate of emergence of bacteria spontaneously resistant to the new compound was also evaluated in relation to representative gram-positive and gram-negative strains. In terms of MIC 50 values, rifaximin showed an intrinsic activity superior to that of the other agents. The emergence of spontaneously resistant strains was assessed with 46 aerobic (staphylococci, enterococci, Proteus spp., Citrobacter freundii, Providencia rettgeri, enteropathogenic, enteroinvasive, enterotoxigenic and entero- hemorrhagic Escherichia coli, and Salmonella enteritidis) and anaerobic (Clostridium spp., Bacteroides spp., Fusobacterium nucleatum and Peptococcus spp.) pathogens, most of them also ammonium producers. Two different methods, broth and agar dilution, were employed. Results: When liquid medium was employed, bacteria capable of sustained growth in 100 μg/ml of rifaximin were obtained after 2–5 transfers with gram-positive aerobic cocci, 2–3 transfers with gram-negative aerobic strains and 2–5 transfers with anaerobic species. At the highest dose used with the agar dilution method (8 × MIC), the frequency of emergence of spontaneously resistant mutants ranged from <1 × 10 –9 to 1.6 × 10 –8 with gram-positive aerobic and anaerobic cocci, while with aerobic and anaerobic gram-negative bacteria, this value ranged from <1 × 10 –9 to 1.7 × 10 –7 . C. difficile showed a particularly low incidence of spontaneously resistant mutants (<1 × 10 –9 ). The low incidence of resistant subpopulations selected by levels of 8 × MIC of rifaximin suggests that the high levels of the drug which were reached in the gastrointestinal lumen may further prevent the selection of mutants. Conclusion: The low toxicity, broad antibacterial activity and very poor absorption from the gastrointestinal tract of rifaximin suggest a potential therapeutic use for this drug in gastrointestinal diseases, as well as in the management of patients with cirrhosis and chronic portal-systemic encephalopathy.