Experimental infection of domestic cats with passaged genotype I Bartonella henselae

The influence of in vitro passage on Bartonella henselae pathogenesis in cats has not been thoroughly evaluated. Our objective was to examine the bacterial kinetics and humoral immune responses in cats experimentally infected with three different in vitro passages of B. henselae F1, a genotype I strain of feline origin. The F1 strain was in vitro passaged 20 and 40 times, and each was inoculated into a group of 5 cats. The kinetics of bacteremia and the feline humoral immune response to bacterial antigens were compared to a previous study involving a group of six cats inoculated with the original F1 strain. Among the three groups of cats, the kinetics of bacteremia profiles and the humoral immune responses to B. henselae lysates were similar. The influence of passage on bacterial membrane proteins was examined. In vitro passage altered the expression of 4/17 (23.5%) bacterial membrane proteins and 6/15 (40%) bacterial membrane antigens. An association between poor seroreactivity to three lysate antigens (15-, 18- and 45kDa), prolonged bacteremia and decreased serum bactericidal activity was noted. Our data show that in vitro passage of B. henselae did not alter the kinetics of bacteremia, including the occurrence of relapsing bacteremia, in experimentally infected cats. This suggests that highly passaged strains may not be suitable for future vaccination studies. Furthermore, in vitro passage results in phenotypic and antigenic changes in the bacterial membrane protein profile, which warrants caution in the interpretation of studies involving passaged B. henselae strains.