title: Subinhibitory concentrations of metronidazole increase biofilm formation in Clostridium difficile strains.
abstract: Resistance mechanism to metronidazole is still poorly understood, even if the number of reports on Clostridium difficile strains with reduced susceptibility to this antibiotic is increasing. In this study, we investigated the ability of the C. difficile strains 7032994, 7032985 and 7032989, showing different susceptibility profiles to metronidazole but all belonging to the PCR ribotype 010, to form biofilm in vitro in presence and absence of subinhibitory concentrations of metronidazole. The quantitative biofilm production assay performed in presence of metronidazole revealed a significant increase in biofilm formation in both the susceptible strain 7032994 and the strain 7032985 exhibiting a reduced susceptibility to this antibiotic, while antibiotic pressure did not affect the biofilm-forming ability of the stable-resistant strain 7032989. Moreover, confocal microscopy analysis showed an abundant biofilm matrix production by the strains 7032994 and 7032885, when grown in presence of metronidazole, but not in the stable-resistant one. These results seem to demonstrate that subinhibitory concentrations of metronidazole are able to enhance the in vitro biofilm production of the above-mentioned PCR ribotype 010 C. difficile strains, susceptible or with reduced susceptibility to this antibiotic, suggesting a possible role of biofilm formation in the multifactorial mechanism of metronidazole resistance developed by C. difficile.
authors.affiliation: Microbial Biofilm Laboratory, IRCCS Fondazione Santa Lucia, 00179 Rome, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Vuotto
authors.affiliation: Department of Infectious, Parasitic and Immune-mediated Diseases, Istituto Superiore di Sanità, 00161 Rome, Italy.
authors.forename: Ines
authors.initials: I
authors.lastname: Moura
authors.affiliation: Department of Infectious, Parasitic and Immune-mediated Diseases, Istituto Superiore di Sanità, 00161 Rome, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Barbanti
authors.affiliation: Microbial Biofilm Laboratory, IRCCS Fondazione Santa Lucia, 00179 Rome, Italy.
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Donelli
authors.affiliation: Department of Infectious, Parasitic and Immune-mediated Diseases, Istituto Superiore di Sanità, 00161 Rome, Italy patrizia.spigaglia@iss.it.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Spigaglia
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001422:Bacterial Adhesion / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects*; D016360:Clostridioides difficile / Q000145:classification / Q000187:drug effects* / Q000502:physiology* / Q000648:ultrastructure; D008795:Metronidazole / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D008795:Metronidazole
keywords: Clostridium difficile; antibiotic resistance; biofilm; metronidazole