title: Antimicrobial effects of commensal oral species are regulated by environmental factors.
abstract: OBJECTIVE
  The objectives of this study are to identify oral commensal species which can inhibit the growth of the main periodontopathogens, to determine the antimicrobial substances involved in these inhibitory activities and to evaluate the influence of environmental factors on the magnitude of these inhibitions.
  
  
  METHODS
  The spotting technique was used to quantify the capacity of 13 commensal species to inhibit the growth of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Prevotella intermedia. By altering experimental conditions (distance between spots and size of spots and concentration of commensal and pathogen) as well as environmental factors (inoculation sequence, oxygen and nutrition availability) the influence of these factors was evaluated. Additionally, the mechanism of inhibition was elucidated by performing inhibition experiments in the presence of peroxidase, trypsin and pepsin and by evaluating acid production.
  
  
  RESULTS
  Streptococcus sanguinis, Streptococcus cristatus, Streptococcus gordonii, Streptococcus parasanguinis, Streptococcus mitis and Streptococcus oralis significantly inhibit the growth of all pathogens. The volume of the spots and concentration of the commensal have a significant positive correlation with the amount of inhibition whereas distance between the spots and concentration of the pathogen reduced the amount of inhibition. Inhibition is only observed when the commensal species are inoculated 24h before the pathogen and is more pronounced under aerobic conditions. Hydrogen peroxide production by the commensal is the main mechanism of inhibition.
  
  
  CONCLUSIONS
  Bacterial antagonism is species specific and depending on experimental as well as environmental conditions. Blocking hydrogen peroxide production neutralizes the inhibitory effect.
  
  
  CONCLUSIONS
  Identifying beneficial oral bacteria and understanding how they inhibit pathogens might help to unravel the mechanisms behind dysbiotic oral diseases. In this context, this study points towards an important role for hydrogen peroxide. The latter might lead in the future to novel preventive strategies for oral health based on improving the antimicrobial properties of commensal oral bacteria.
authors.affiliation: Department of Oral Health Sciences, KU Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium. Electronic address: esteban.rodriguezherrero@med.kuleuven.be.
authors.forename: Esteban Rodriguez
authors.initials: ER
authors.lastname: Herrero
authors.affiliation: Department of Oral Health Sciences, KU Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium.
authors.forename: Vera
authors.initials: V
authors.lastname: Slomka
authors.affiliation: Bio- and Chemical Systems Technology, Reactor Engineering and Safety, Department of Chemical Engineering, KU Leuven (University of Leuven), Leuven Chem&Tech, Celestijnenlaan 200F (bus 2424), 3001 Leuven, Belgium.
authors.forename: Kristel
authors.initials: K
authors.lastname: Bernaerts
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMet), Ghent University, Coupure links 653, 9000 Ghent, Belgium.
authors.forename: Nico
authors.initials: N
authors.lastname: Boon
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMet), Ghent University, Coupure links 653, 9000 Ghent, Belgium.
authors.forename: Emma
authors.initials: E
authors.lastname: Hernandez-Sanabria
authors.affiliation: Department of Oral Health Sciences, KU Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium.
authors.forename: Bernardo Born
authors.initials: BB
authors.lastname: Passoni
authors.affiliation: Department of Oral Health Sciences, KU Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium; Dentistry, University Hospitals Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Quirynen
authors.affiliation: Department of Oral Health Sciences, KU Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium; Dentistry, University Hospitals Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium. Electronic address: wim.teughels@med.kuleuven.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Teughels
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D000898:Antibiosis; D001430:Bacteriocins / Q000096:biosynthesis; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D009055:Mouth / Q000382:microbiology*; D010519:Periodontium / Q000382:microbiology; D016966:Porphyromonas gingivalis / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D018713:Prevotella intermedia / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D013291:Streptococcus / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D013559:Symbiosis / Q000502:physiology*
chemical_list: D001430:Bacteriocins; D006861:Hydrogen Peroxide
keywords: Bacteriocins; Beneficial bacteria; Commensal bacteria; Hydrogen peroxide; Periodontal pathogens; Streptococcus