In order to identify immunoreactive Bartonella henselae
proteins, B. henselae antiserum from an experimentally infected cat was used to screen a B. henselae genomic
DNA expression library. One immunoreactive phage clone contained a gene (p26) with significant
nucleotide identity with orthologs in brucellae, bartonellae, and several plant-associated bacteria. p26 gene sequences from four B. henselae strains, one B. koehlerae strain, and one B. clarridgeiae strain were cloned. Comparative nucleotide sequence analysis showed that p26 is a potential marker for molecular diagnosis of
infection, as well as for identification to species level and genotyping of Bartonella sp. isolates. Alignment of the predicted amino acid sequences illustrated conserved putative
protein features including a hydrophobic transmembrane region, a
peptide cleavage site, and four dominant antigenic sites. Expression of p26 in Escherichia coli produced two
proteins (26 and 27.5 kDa), both of which were reactive with feline anti-B. henselae
antisera. Furthermore, murine hyperimmune serum raised against either
recombinant protein reacted with both
proteins. No reactivity to either
recombinant protein was detected in nonimmune serum, and reactivity persisted as long as 20 weeks for one cat. The p26
protein product is an immunodominant
antigen that is expressed during
infection in cats as a preprotein and is subsequently cleaved to form mature P26.