WOLBACHIA INFECTION IN AN IXODES SCAPULARIS-DERIVED TICK CELL LINE

Abstract

Wolbachia, an obligate intracellular bacterial endosymbiont, is gaining recognition for its ability to reduce the transmission of arboviruses by Aedes aegypti mosquitoes, leading to its use in dengue virus control programs. Some Wolbachia strains can be propagated in vitro in insect or tick cell lines, facilitating the study of host-bacteria interactions. Here, we present findings from a microscopic study of a Wolbachia endosymbiont (wCfe) that was isolated from Malaysian Ctenocephalides felis fleas, in an Ixodes scapularis-derived tick cell line (ISE6). The presence of Wolbachia in cultures was visualized using Giemsa staining at 0, 1-, 7-, 14-, and 21 days post-infection. The cytocentrifuge smears were examined under a compound microscope at 1000× magnification, and images were captured using XCamView software. Comparison of Giemsa-stained uninfected and wCfe-infected ISE6 cultures revealed that the proportion of infected cells increased over the 21-day examination period. Bacteria were visible in the cell cytoplasm, often clustering near the nucleus. Heavily infected cells became more fragile and burst, and the total number of cells in the culture reduced following a severe infection. Despite extensive cytopathic effects seen by 29 days post-infection, not all cells died; two months later, the surviving cells appeared to have become persistently infected with wCfe. In conclusion, based on the successful observation of wCfe infection dynamics within the ISE6 cells, the study confirms that this tick cell line is suitable for propagating different strains of Wolbachia. Our results also show that light microscopy plays a useful role in monitoring the course of Wolbachia infection in arthropod cell lines and could be used to complement electron microscopy and molecular quantification studies.