Dermacentor marginatus and Ixodes ricinus ticks versus L929 and Vero cell lines in Rickettsia slovaca life cycle evaluated by quantitative real time PCR

Abstract

Ticks transmit many different pathogens to animals, humans and their pets. Rickettsia slovaca, as a member of the spotted-fever-group rickettsiae is an agent of the human disease Tick-borne lymphadenopathy (TIBOLA), also called Dermacentor-borne necrosis erythema and lymphadenopathy (DEBONEL), which occurs from the Mediterranean to central Europe, transmitted by Dermacentor reticulatus and Dermacentor marginatus (Acari: Ixodidae). In this study, quantitative real time PCR was used to characterize the growth of R. slovaca, strain B in static (mammalian L929 and Vero cells without replacement of growth medium) and dynamic (D. marginatus and Ixodes ricinus ticks) cultivation systems. Curves of bacterial growth in static cultivations were modeled with exponential, stationary and death phases, whereas in dynamic systems the stationary phase was absent. The highest point of multiplication of R. slovaca was recorded on the 4th day post infection in both cell lines and the rickettsial DNA copy number in L929 and Vero cells at this point was 21 and 27 times greater than rickettsial DNA copy number of inoculum, respectively. In the dynamic system, the highest point of multiplication was on the 21th and 12th day after feeding of ticks and rickettsial DNA copy numbers were 7,482 and 865 times greater than the inoculum in D. marginatus and I. ricinus, respectively. Life cycle of R. slovaca in mammalian cell lines was shorter; supposedly, bacteria destroyed these cells and ticks, especially D. marginatus, were considered a more appropriate environment.