Cultivation of Bartonella henselae in an Ixodes ricinus cell line to assess this tick as a potential reservoir of the bacterium.

Introduction: Bartonella spp. are gram-negative, facultative intracellular bacteria with zoonotic potential. These microorganisms are emerging vector-borne pathogens distributed worldwide and infecting humans, domestic mammals and wildlife. This study investigated the possibility of culturing Bartonella henselae in a tick cell line derived from Ixodes ricinus.

Material and methods: The Ixodes ricinus embryonic cell line (IRE/CTVM19) and the Houston-1 strain of B. henselae were used for culture studies. Replication of B. henselae was quantified with the use of a SYBR Green real-time PCR and transcribed complementary DNA (cDNA) in samples collected separately from the supernatant and monolayer of culture from 1 to 9 days post-infection (d.p.i.). Identification of B. henselae was based on the detection of a fragment of the ribC gene encoding riboflavin synthase. Quantification was performed indirectly by determining the threshold cycle.

Results: Microscopic observations confirmed that infection with B. henselae did not show any visible negative effect on tick cells. The quantity of B. henselae cDNA from the monolayer remained low, and a slight increase was observed at 4, 8 and 9 d.p.i. Significantly, the highest amount of B. henselae was observed at 2 d.p.i. in samples isolated from the supernatant.

Conclusion: The maintenance of live B. henselae in an I. ricinus-derived cell line was confirmed. The low level of multiplication in the tick cell line suggested a limited role of I. ricinus as a reservoir of B. henselae. The IRE/CTVM19 tick cell line is suitable for culture of B. henselae, and this model may be useful in further studies.