title: Rapid killing of Capnocytophaga canimorsus and Capnocytophaga cynodegmi by human whole blood and serum is mediated via the complement system.
abstract: OBJECTIVE
  Capnocytophaga canimorsus (Cani) and Capnocytophaga cynodegmi (Cyno) are found in the oral cavities of dogs and cats. They can be transmitted to humans via licks or bites and cause wound infections as well as severe systemic infections. Cani is considered to be more pathogenic than Cyno, but the pathophysiological mechanisms are not elucidated. Cani has been suggested to be resistant to serum bactericidal effects. Thus, we hypothesized that the more invasive Cani would exhibit a higher degree of serum-resistance than the less pathogenic Cyno.
  
  
  METHODS
  Whole blood and serum bactericidal assays were performed against Cani- (n = 8) and Cyno-strains (n = 15) isolated from blood and wound-specimens, respectively. Analysis of complement-function was performed by heat-inactivation, EGTA-treatment and by using C1q-depleted serum. Serum and whole blood were collected from healthy individuals and from patients (n = 3) with a history of sepsis caused by Cani.
  
  
  RESULTS
  Both Cani and Cyno were equally susceptible to human whole blood and serum. Cani was preferentially killed by the classical pathway of the complement-system whereas Cyno was killed by a partly different mechanism. Serum from 2/3 Cani-infected patients were deficient in MBL-activity but still exhibited the same killing effect as control sera.
  
  
  CONCLUSIONS
  Both Cani and Cyno were readily killed by human whole blood and serum in a complement-dependent way. Thus, it is not likely that serum bactericidal capacity is the key determinant for the clinical outcome in Cani or Cyno-infections.
authors.affiliation: Div of Clinical Microbiology, F68, Department of Laboratory Medicine, Karolinska Institutet and Karolinska University Hospital, Huddinge, Stockholm, Sweden ; Department of Medicine, Center for Infectious Medicine (CIM), Karolinska Institutet and Karolinska University Hospital, Huddinge, Stockholm, Sweden.
authors.forename: Salah
authors.initials: S
authors.lastname: Zangenah
authors.affiliation: Div of Clinical Microbiology, F68, Department of Laboratory Medicine, Karolinska Institutet and Karolinska University Hospital, Huddinge, Stockholm, Sweden ; Department of Medicine, Center for Infectious Medicine (CIM), Karolinska Institutet and Karolinska University Hospital, Huddinge, Stockholm, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Bergman
keywords: Alternative pathway; Capnocytophaga canimorsus; Capnocytophaga cynodegmi; Classical pathway; Complement system; Mannose binding lectin deficiency; Serum killing assay; Whole blood killing assay