title: Virulence mechanism of bacteria in mixed infection: attenuation of cytokine levels and evasion of polymorphonuclear leukocyte phagocytosis.
abstract: BACKGROUND
  The objective of the present study is to evaluate the effect of bacterial viability on the virulence of mixed infection.
  
  
  METHODS
  Expression of pro- and anti-inflammatory cytokines (interleukin [IL]-1β and IL-10, respectively) was tested in vivo, following live versus heat-killed infection (mono or mixed), using the mouse chamber model of infection. Ex vivo, phagocytosis of fluorescently labeled bacteria was tested in primary mouse polymorphonuclear leukocytes by flow cytometry.
  
  
  RESULTS
  In monoinfection, heat-killed Porphyromonas gingivalis led to augmented levels of IL-1β 2 hours postinfection, whereas IL-10 levels remained unaffected. Phagocytosis of heat-killed P. gingivalis was reduced compared with that of the live P. gingivalis, whereas phagocytosis of heat-killed Fusobacterium nucleatum was augmented compared with that of live F. nucleatum. In mixed infection, both IL-1β and IL-10 levels were augmented 24 hours postinfection when the bacteria were heat-killed. Although the phagocytosis pattern of F. nucleatum in the mixed infection remained similar to that upon monoinfection, phagocytosis of P. gingivalis was reduced following mixed infection.
  
  
  CONCLUSIONS
  The inflammatory response to live mixed infection is attenuated with reduced phagocytosis, compared with that of heat-killed mixed infection. The lower response to live mixed infection could stem from a mechanism enabling the bacteria to evade the host response, thereby increasing bacterial survival.
authors.affiliation: Department of Periodontology, Faculty of Dental Medicine, The Hebrew University-Hadassah Medical Center, Jerusalem, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Polak
authors.forename: Lior
authors.initials: L
authors.lastname: Shapira
authors.forename: Ervin I
authors.initials: EI
authors.lastname: Weiss
authors.forename: Yael
authors.initials: Y
authors.lastname: Houri-Haddad
mesh_terms: D000818:Animals; D001431:Bacteriological Techniques; D016866:Bacteroidaceae Infections / Q000276:immunology*; D060085:Coinfection / Q000276:immunology*; D015194:Diffusion Chambers, Culture; D005260:Female; D005434:Flow Cytometry; D005674:Fusobacterium Infections / Q000276:immunology*; D016967:Fusobacterium nucleatum / Q000276:immunology / Q000472:pathogenicity*; D057131:Immune Evasion / Q000276:immunology; D016753:Interleukin-10 / Q000032:analysis; D053583:Interleukin-1beta / Q000032:analysis; D007378:Interleukins / Q000032:analysis*; D051379:Mice; D050296:Microbial Viability / Q000276:immunology; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D016966:Porphyromonas gingivalis / Q000276:immunology / Q000472:pathogenicity*; D013997:Time Factors; D014774:Virulence
chemical_list: C556062:IL10 protein, mouse; D053583:Interleukin-1beta; D007378:Interleukins; D016753:Interleukin-10