Development of the microsporidian parasite, Loma salmonae, in a rainbow trout gill epithelial cell line (RTG-1): evidence of xenoma development in vitro

Abstract

Growth and propagation of fish-infecting microsporidians within cell culture has been more difficult to achieve than for insect- and human-infecting microsporidians. Fish microsporidia tend to elicit xenoma development rather than diffuse growth in vivo, and this process likely increases host specificity. We present evidence that the fish microsporidian, Loma salmonae, has the capacity to develop xenomas within a rainbow trout gill epithelial cell line (RTG-1). Spore numbers increased over a 4 weeks period within cell culture flasks. Xenoma-like structures were observed using phase contrast microscopy, and then confirmed using transmission electron microscopy. Optimization of the L. salmonae-RTG-1 cell model has important implications in elucidating the process of xenoma development induced by microsporidian parasites.

Development of a continuous cell line from larval Atlantic cod (Gadus morhua) and its use in the study of the microsporidian, Loma morhua

“…The consistent visual observation of large mounds of spore laden aggregates after 2 weeks of L. morhua exposure in GML‐5 cells, indicate the possibility of xenoma‐like formation occurring in vitro, similar to the observations reported by McConnachie et al. () of xenoma formation in a trout gill cell line infected with Loma salmonae . Future investigations could focus on the process of xenoma development, mechanisms of cellular fusion and effects of antimicrosporidial agents, among many other areas of investigation that the availability of this new cell line opens up.…”

“…Furthermore, given that McConnachie et al. () cultured L. salmonae , microsporidians that normally affect gills of salmonids, in a rainbow trout gill cell line, it appears that host and tissue specificity may also be preserved in vitro, and the observations reported by Lores et al. (); Kumar et al.…”

“…Given the market value of live fish and the relative complexity of in vivo studies, additional research tools are required for timely and efficient means of improving livestock management and production methods. Cell culture and other in vitro methodologies have proven invaluable tools for studies into fish physiology and parasitology, advancing our understanding of piscine pathogens, facilitating the production of vaccines and preliminary evaluations of therapeutic treatments (Bols, ; Bols, Pham, Dayeh, & Lee, ; Hightower & Renfro, ; Lee, Dayeh, Schirmer, & Bols, ; McConnachie, Sheppard, Wright, & Speare, ; Monaghan et al., ; Pinheiro & Bols, ; Villena, ; Woo & Li, ).…”

“…Much of the work to date, however, has focused principally on arthropod and mammal‐infecting microsporidians, with very few fish‐infecting species represented as in vitro infection models (reviewed in Monaghan et al., ). Nonetheless, promising recent reports with fish cell lines are proving useful for studying fish‐infecting microsporidians (McConnachie et al., ; Saleh, Kumar, Abdel‐Baki, El‐Matbouli, & Al‐Quraishy, ) or other microsporidians (Monaghan, Rumney, Vo, Bols, & Lee, ).…”

“…physiology and parasitology, advancing our understanding of piscine pathogens, facilitating the production of vaccines and preliminary evaluations of therapeutic treatments (Bols, 1991;Bols, Pham, Dayeh, & Lee, 2017;Hightower & Renfro, 1988;Lee, Dayeh, Schirmer, & Bols, 2009;McConnachie, Sheppard, Wright, & Speare, 2015;Monaghan et al, 2009;Pinheiro & Bols, 2013;Villena, 2003;Woo & Li, 1990).…”