Inter- and intraspecies-specific adhesion of Lyme borreliae to human keratinocytes

Spirochetes have developed sophisticated means to successfully colonize host tissues and survive in unfavorable environments. Attachment to human cells is thought to be a key step for the establishment of an infection that causes multiple clinical symptoms. Infection of host tissues largely depends on the ability of spirochetes to attach to different cell types. In this study, we examine the ability of spirochetes belonging to seven distinct genospecies (Borrelia (B.) burgdorferi sensu stricto (s.s.), B. afzelii, B. garinii, B. spielmanii, B. bavariensis, B. lusitaniae, and B. valaisiana) to adhere to human keratinocytes. Among the genospecies analyzed, B. valaisiana and B. spielmanii showed the strongest adherence while B. bavariensis, B. garinii and B. afzelii displayed moderate binding activity. By contrast, only a few cells of B. burgdorferi s.s. and B. lusitaniae bound to keratinocytes. Furthermore, intra-species differences have also been observed among B. garinii, B. bavariensis, B. afzelii, and in particular B. valaisiana. To further assess the role of infection-associated borrelial outer surface proteins for mediating interaction to human cells, a non-adherent and non-infectious B. garinii strains producing distinct complement regulator-acquiring surface proteins (CRASP) were employed. Interestingly, binding capacity to human keratinocytes increased up to four-fold in B. garinii cells producing ErpC but not CspA, CspZ or ErpP compared to wild-type B. garinii cells lacking CRASPs. Taken together, these data provide evidence that distinct borrelial genospecies differ in their ability to bind to human keratinocytes and, in addition, support a role of ErpC as a potential adhesin of spirochetes.