Similarities in murine infection and immune response to Borrelia bissettii and Borrelia burgdorferi sensu stricto

In 1982, Borrelia burgdorferi sensu stricto (ss) was identified as the aetiological agent of Lyme disease. Since then an increasing number of Borrelia burgdorferi sensu lato (sl) species have been isolated in the United States. To date, many of these species remain understudied despite mounting evidence associating them with human illness. Borrelia bissettii is a spirochaete closely related to B. burgdorferi that has been loosely associated with human illness. Using an experimental murine infection model, we compared the infectivity and humoral immune response with a North American isolate of B. bissettii and B. burgdorferi using culture, molecular and serological methods. The original B. bissettii cultures were unable to infect immunocompetent mice, but were confirmed to be infectious after adaptation in immunodeficient animals. B. bissettii infection resulted in spirochaete burdens similar to B. burgdorferi in skin, heart and bladder whereas significantly lower burdens were observed in the joint tissues. B. bissettii induced an antibody response similar to B. burgdorferi as measured by both immunoblotting and the C6 ELISA. Additionally, this isolate of B. bissettii was sequenced on the Ion Torrent PGM, which successfully identified many genes orthologous to mammalian virulence factors described in B. burgdorferi. Similarities seen between both infections in this well-characterized murine model contribute to our understanding of the potential pathogenic nature of B. bissettii. Infection dynamics of B. bissettii, and especially the induced humoral response, are similar to B. burgdorferi, suggesting this species may contribute to the epidemiology of human borreliosis.