Proteomic analysis of Rickettsia akari proposes a 44 kDa-OMP as a potential biomarker for Rickettsialpox diagnosis

Background: Rickettsialpox is a febrile illness caused by the mite-borne pathogen Rickettsia akari . Several cases of this disease are reported worldwide. Nevertheless, the relationship between the immunogenicity of R. akari and the disease development remains poorly understood. Therefore, misdiagnosis is frequent. Our study is aimed to identify immunogenic proteins that may improve disease recognition and enhance subsequent treatment. To achieve this goal, two proteomics methodologies were applied, followed by immunoblot confirmation. Results: : Three hundred and sixteen unique proteins were identified in the whole-cell extract of R. akari . The most represented protein groups were found to be those involved in translation, post-translational modifications, energy production, and cell wall development. A significant number of proteins belonged to amino acid transport and intracellular trafficking. Also, some proteins affecting the virulence were detected. In silico analysis of membrane enriched proteins revealed 25 putative outer membrane proteins containing beta-barrel structure and 11 proteins having a secretion signal peptide sequence. Using rabbit and patient sera, various immunoreactive proteins were identified from which the 44 kDa uncharacterized protein (A8GP63) has demonstrated a unique detection capability. It positively distinguished the sera of patients with Rickettsialpox from other rickettsia positive patient sera. Conclusion: Our proteomic analysis certainly contributed to the knowledge of the pathogenesis of R. akari. The result obtained may also serve as a guideline for a more accurate diagnosis of rickettsial diseases. Identified R. akari antigenic protein can be design as a unique marker of rickettsialpox and used as a target for the development of more effective treatment.