Structure and viability of atypical morphological forms of L yme disease spirochetes

Abstract

Spirochetes Borrelia burgdorferi sensu lato are the causative agents of Lyme disease transmitted by the hard ticks of the genus Ixodes. Spirochetes are motile bacteria with typical flat‐wave morphology. These features are crucial for efficient dissemination and evasion of immune responses. However, several reports described presence of non‐motile atypical morphologies, e.g. rod‐shaped forms, looped/ring shaped forms and spherical/cystic forms called round bodies (RBs). These forms were observed in the cerebral cortex of patient with chronic Lyme neuroborreliosis [1]. Recently, we proved long term survival of Borrelia in patients after extended antibiotic treatment by successful isolation of live spirochetes [2]. Now, we would like to answer questions, (i) whether RBs represent resistant forms of persisting Lyme disease spirochetes and (ii) whether the transformation of flat‐waved spirochetes into RBs forms influences the capability to withstand unfavourable environmental conditions. For this purpose, we studied morphology and three dimensional arrangements of spirochetes isolated from patients by transmission electron microscopy and electron tomography on serial resin sections and negatively stained spirochetes. Next, using a modification of our novel approach combining cryo‐fluorescence and cryo‐scanning electron microscopy, we interconnect viability assay with visualization of morphology at high resolution [3]. Viability of GFP expressing spirochetes in a response to host sera was assessed using propidium iodide exclusion method. Obtained results confirmed different susceptibility to different host sera, previously described by our colleagues [4]. We confirmed the formation/viability of RB forms under specific conditions.