الفهرس 
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Abstract
The aim of present study is to investigate the role of complement system in the killing of gram negative bacteria specially K. pneumoniae. This was done by studying relationship between factor H binding protein and serum resistance of K. pneumoniae to by its binding to outer membrane proteins of K. pneumoniae. A total of sixty clinical isolates of K. pneumoniae were collected from Mansoura University Hospitals, Egypt. Twenty isolates were collected from blood samples, twenty isolates from urine samples, and the last twenty from sputum samples. Pooled normal human serums were collected from different healthy people. The collected isolates were firstly tested for serum bactericidal assay. Most of K. pneumoniae exhibited resistance to NHS. 100% of blood samples, 75% of urine samples, and 60% of sputum samples are resistant to serum.The ability of K. pneumoniae to activate alternative pathway of the complement system was determined via detection of serum killing. We used low concentration of serum in BBS which supports the lectin and the classical pathways and high serum concentration in presence of Mg+2 in BBS buffer with EGTA which support the alternative pathway. To differentiate between serum sensitive and serum resistance isolates we used ELISA technique to detect Factor H binding and C3 deposition on surface of the bacteria by using several dilutions of normal human serum. This was done by relative quantification of factor H binding and cleavage product of C3 respectively that can attach to ELISA plate by adding an antibody directed against them. This assay was on 3 serum resistance isolates and 3 serum sensitive isolates. It was shown that low binding of factor H and high C3b deposition via the AP on serum sensitive isolates was observed while high binding of factor H and no C3b deposition was detected on the surface of serum resistant isolates It was shown also a significant high levels of complement C3b deposition via the LP/CP were observed on both serum resistant and serum sensitive isolates. The SDS-PAGE analysis and western blot showed strong bands with outer membrane proteins of serum resistant isolates of K. pneumoniae while it showed some faint bands with serum sensitive ones at 31, 29 kDa. Western blotting applied to the outer membrane proteins using anti-factor H monoclonal antibodies. The pathogenicity of serum resistant and serum sensitive K. pneumoniae was assessed in an in vivo mouse pneumonia model.by using two groups of BALB/c mice. Two groups were injected intranasally injected with either of the serum resistant isolate and the second group was injected with serum sensitive isolate. A significant increase in survival number of resistant bacteria in the lungs and blood of first group compared to the second group.