title: Is hydrogen peroxide responsible for the inhibitory activity of alpha-haemolytic streptococci sampled from the nasopharynx?
abstract: OBJECTIVE
  The inhibitory effect of alpha-haemolytic Streptococci (AHS) in vitro on the three commonest otitis media pathogens, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, was previously investigated. The aim of this study was to determine the mechanism of this inhibitory activity.
  
  
  RESULTS
  When fractions of AHS filtrate were assayed to determine their inhibitory activity after size-exclusion chromatography, the inhibitory activity was found in the fractions with a low molecular weight. The inhibitory effect was completely reversed when catalase was added to the cell-free filtrate of AHS. A quantitative method also revealed high production (approximately 3 mmol/l) of hydrogen peroxide in the AHS filtrate with the best inhibitory activity. Electron microscopy of bacteria exposed to AHS filtrate with an inhibitory effect showed changes similar to bacteria exposed to hydrogen peroxide.
  
  
  CONCLUSIONS
  We conclude that the inhibitory effect of AHS is most likely due to the production of hydrogen peroxide. The significance of hydrogen peroxide production of AHS is discussed in relation to the non-specific and specific mucosal defence systems.
authors.affiliation: Department of Clinical Sciences, Otorhinolaryngology, Umeå University, Umeå, Sweden. krister.tano@nll.se
authors.forename: Krister
authors.initials: K
authors.lastname: Tano
authors.forename: Eva
authors.initials: E
authors.lastname: Grahn Håkansson
authors.forename: Pia
authors.initials: P
authors.lastname: Wallbrandt
authors.forename: Daniel
authors.initials: D
authors.lastname: Rönnqvist
authors.forename: Stig E
authors.initials: SE
authors.lastname: Holm
authors.forename: Sten
authors.initials: S
authors.lastname: Hellström
mesh_terms: D018407:Bacterial Physiological Phenomena; D006193:Haemophilus influenzae / Q000254:growth & development; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D001936:Moraxella catarrhalis / Q000254:growth & development; D009305:Nasopharynx / Q000382:microbiology*; D010033:Otitis Media / Q000382:microbiology*; D013296:Streptococcus pneumoniae / Q000254:growth & development; D034363:Viridans Streptococci / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D006861:Hydrogen Peroxide