Serum resistance of Acinetobacter baumannii through the binding of factor H to outer membrane proteins.
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.
Kim
Sang Woo
SW
Department of Microbiology, Kyungpook National University School of Medicine, Daegu, Korea.
Choi
Chul Hee
CH
Moon
Dong Chan
DC
Jin
Jong Sook
JS
Lee
Jung Hwa
JH
Shin
Ji-Hyun
JH
Kim
Jung Min
JM
Lee
Yoo Chul
YC
Seol
Sung Yong
SY
Cho
Dong Taek
DT
Lee
Je Chul
JC
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
D001425:Bacterial Outer Membrane Proteins; C078167:OMPA outer membrane proteins; D017242:Complement Factor H