title: Deficiency of the ferrous iron transporter FeoAB is linked with metronidazole resistance in Bacteroides fragilis.
abstract: BACKGROUND
  Metronidazole is the most commonly used antimicrobial for Bacteroides fragilis infections and is recommended for prophylaxis of colorectal surgery. Metronidazole resistance is increasing and the mechanisms of resistance are not clear.
  
  
  METHODS
  A transposon mutant library was generated in B. fragilis 638R (BF638R) to identify the genetic loci associated with resistance to metronidazole.
  
  
  RESULTS
  Thirty-two independently isolated metronidazole-resistant mutants had a transposon insertion in BF638R_1421 that encodes the ferrous transport fusion protein (feoAB). Deletion of feoAB resulted in a 10-fold increased MIC of metronidazole for the strain. The metronidazole MIC for the feoAB mutant was similar to that for the parent strain when grown on media supplemented with excess iron, suggesting that the increase seen in the MIC of metronidazole was due to reduced cellular iron transport in the feoAB mutant. The furA gene repressed feoAB transcription in an iron-dependent manner and disruption of furA resulted in constitutive transcription of feoAB, regardless of whether or not iron was present. However, disruption of feoAB also diminished the capacity of BF638R to grow in a mouse intraperitoneal abscess model, suggesting that inorganic ferrous iron assimilation is essential for B. fragilis survival in vivo.
  
  
  CONCLUSIONS
  Selection for feoAB mutations as a result of metronidazole treatment will disable the pathogenic potential of B. fragilis and could contribute to the clinical efficacy of metronidazole. While mutations in feoAB are probably not a direct cause of clinical resistance, this study provides a key insight into intracellular metronidazole activity and the link with intracellular iron homeostasis.
authors.affiliation: GLAVAHCS, Los Angeles, CA, USA UCLA School of Medicine, Los Angeles, CA, USA.
authors.forename: Yaligara
authors.initials: Y
authors.lastname: Veeranagouda
authors.affiliation: GLAVAHCS, Los Angeles, CA, USA.
authors.forename: Fasahath
authors.initials: F
authors.lastname: Husain
authors.affiliation: GLAVAHCS, Los Angeles, CA, USA.
authors.forename: Renata
authors.initials: R
authors.lastname: Boente
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast, UK.
authors.forename: Jane
authors.initials: J
authors.lastname: Moore
authors.affiliation: East Carolina University Brody School of Medicine, Greenville, NC, USA.
authors.forename: C Jeffrey
authors.initials: CJ
authors.lastname: Smith
authors.affiliation: East Carolina University Brody School of Medicine, Greenville, NC, USA.
authors.forename: Edson R
authors.initials: ER
authors.lastname: Rocha
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast, UK.
authors.forename: Sheila
authors.initials: S
authors.lastname: Patrick
authors.affiliation: GLAVAHCS, Los Angeles, CA, USA UCLA School of Medicine, Los Angeles, CA, USA hwexler@ucla.edu.
authors.forename: Hannah M
authors.initials: HM
authors.lastname: Wexler
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001441:Bacteroides fragilis / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D027682:Cation Transport Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005296:Ferrous Compounds / Q000378:metabolism; D017353:Gene Deletion; D015870:Gene Expression; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D015723:Gene Library; D023061:Gene Order; D005838:Genotype; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000235:genetics; D009154:Mutation; D014158:Transcription, Genetic; D059467:Transcriptome
chemical_list: D000900:Anti-Bacterial Agents; D027682:Cation Transport Proteins; D004251:DNA Transposable Elements; D005296:Ferrous Compounds; D008795:Metronidazole
keywords: anaerobic bacteria; antimicrobial resistance; iron transport; transposon mutant