Bartonella henselae : growth, metabolism, and immunogenic outer membrane proteins
Chenoweth, Matthew Ryan
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Bartonella henselae is a recently discovered zoonotic pathogen whose natural reservoir is the domestic cat, but it also causes significant human illness. To treat and prevent disease due to B. henselae infection, the pathogenic mechanisms must be understood. A major obstacle in Bartonella research has been the lack of an appropriate growth medium. I have developed a liquid culture medium that supports high levels of B. henselae growth. Using this medium, the unusual growth and metabolic properties of the bacterium were investigated. Unlike typical blood-borne pathogens, B. henselae did not utilize glucose. Rather, it catabolized amino acids to tricarboxylic acid cycle intermediates, which can then be used to generate energy. After reaching maximum cell density, the number of viable cells present in the culture rapidly dropped to zero, despite the presence of sufficient nutrients for continued growth. This unusual growth phenotype, termed the "death phase", was found to correlate with phage induction, which may be tied to the organism’s growth rate. The medium also permitted the isolation of B. henselae from the blood of infected cats, and serial passage of B. henselae in the medium did not hinder the bacterium’s ability to establish chronic infections in cats. After developing the medium, we investigated the interaction of the feline immune system with components of B. henselae’s outer membrane (OM). Immune sera from naturally and experimentally infected cats were used to identify commonly recognized antigens in the OM. Interestingly, lipopolysaccharide and the majority of OM proteins did not stimulate an immune response. Several B. henselae OM proteins were recognized by all sera screened, but the most antigenic proteins were relatively minor components of the OM. These surface proteins likely play a key role in the infection process, and are also excellent candidates for a feline vaccine to eliminate the B. henselae reservoir.