title: Serum resistance of Acinetobacter baumannii through the binding of factor H to outer membrane proteins.
abstract: Bacteremia is a common systemic disease caused by Acinetobacter baumannii, an important hospital-acquired pathogen among critically ill patients. The complement system is central to innate immune defense against invading bacteria in the blood. The present study investigated the susceptibility of clinical A. baumannii isolates to normal human sera (NHS), and determined the resistance mechanism of A. baumannii against complement-mediated lysis. The survival of A. baumannii isolates from bacteremic patients was significantly decreased in undiluted NHS, but they were resistant to 40% NHS. The alternative complement pathway was responsible for the direct killing of bacteria. The main regulator of the alternative complement pathway, factor H, bound to the surface of live A. baumannii treated with NHS. Factor H interacted with the outer membrane proteins with molecular sizes of 38 (AbOmpA), 32, and 24 kDa. The isogenic AbOmpA(-) mutant was highly susceptible to NHS in comparison with the wild-type A. baumannii strain, suggesting that AbOmpA was an important complement regulator-acquiring surface protein. These results indicate that A. baumannii evades complement attack through the acquisition of factor H to their surface.
authors.affiliation: Department of Microbiology, Kyungpook National University School of Medicine, Daegu, Korea.
authors.forename: Sang Woo
authors.initials: SW
authors.lastname: Kim
authors.forename: Chul Hee
authors.initials: CH
authors.lastname: Choi
authors.forename: Dong Chan
authors.initials: DC
authors.lastname: Moon
authors.forename: Jong Sook
authors.initials: JS
authors.lastname: Jin
authors.forename: Jung Hwa
authors.initials: JH
authors.lastname: Lee
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Shin
authors.forename: Jung Min
authors.initials: JM
authors.lastname: Kim
authors.forename: Yoo Chul
authors.initials: YC
authors.lastname: Lee
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Seol
authors.forename: Dong Taek
authors.initials: DT
authors.lastname: Cho
authors.forename: Je Chul
authors.initials: JC
authors.lastname: Lee
mesh_terms: D000151:Acinetobacter Infections / Q000276:immunology / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000276:immunology* / Q000302:isolation & purification; D016470:Bacteremia / Q000276:immunology / Q000382:microbiology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001770:Blood Bactericidal Activity; D017242:Complement Factor H / Q000378:metabolism*; D016638:Critical Illness; D055786:Gene Knockout Techniques; D006801:Humans; D050296:Microbial Viability; D008970:Molecular Weight; D011485:Protein Binding
chemical_list: D001425:Bacterial Outer Membrane Proteins; C078167:OMPA outer membrane proteins; D017242:Complement Factor H