title: Lactate dehydrogenase activity in Bacteroides fragilis group strains with induced resistance to metronidazole.
abstract: The aims of this study were to induce in vitro metronidazole resistance in nim-negative Bacteroides fragilis group strains and to determine the lactate dehydrogenase (LDH) activity of the induced strains. A collection of B. fragilis group strains were identified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). Minimum inhibitory concentrations (MICs) for metronidazole were determined by the agar dilution technique. The presence of nim genes was screened by PCR. A sample of 52 nim-negative metronidazole-susceptible strains were selected at random and were exposed to metronidazole in the resistance induction experiment. LDH activity was measured by spectrophotometry. Of the 52 selected strains, 12 (23.1%) acquired resistance to metronidazole. MICs ranged from 8mg/L to 96mg/L. Eight of the twelve induced strains displayed decreased LDH activity, whilst only one expressed a significant increase in LDH activity with LDH values of 49.1U/mg and 222.0U/mg, respectively. In conclusion, in vitro induction of metronidazole resistance could be selected in nim-negative B. fragilis group strains. A statistically significant decrease in LDH activity was in contrast to previous findings in which, underlying higher metronidazole MICs, an increase in LDH activity compensated for the decreased activity of pyruvate-ferredoxin oxidoreductase (PFOR). These findings could be explained if the induction caused only physiological and not genetic changes. We believe that genetic mutations in the B. fragilis strain that demonstrated an emergent increase in LDH activity were responsible for the increased activity.
authors.affiliation: Department of Clinical and Molecular Microbiology, University Clinical Hospital Centre Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia. Electronic address: aleksandra.stanko@yahoo.com.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Presečki Stanko
authors.affiliation: Institute of Clinical Microbiology, University of Szeged, Semmelweis u. 6, H-6725 Szeged, Hungary.
authors.forename: Jozsef
authors.initials: J
authors.lastname: Sóki
authors.affiliation: Department of Clinical and Molecular Microbiology, University Clinical Hospital Centre Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia.
authors.forename: Dijana
authors.initials: D
authors.lastname: Varda Brkić
authors.affiliation: Department of Clinical and Molecular Microbiology, University Clinical Hospital Centre Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia.
authors.forename: Vanda
authors.initials: V
authors.lastname: Plečko
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001441:Bacteroides fragilis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D024881:Drug Resistance, Bacterial; D045022:Lactate Dehydrogenases / Q000378:metabolism*; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests
chemical_list: D000900:Anti-Bacterial Agents; D008795:Metronidazole; D045022:Lactate Dehydrogenases
keywords: Bacteroides fragilis; Lactate dehydrogenase; Metronidazole resistance; nim gene