Larva of greater wax moth Galleria mellonella is a suitable alternative host for the fish pathogen Francisella noatunensis subsp. orientalis

Abstract

Background: Francisella noatunensis subsp. orientalis (Fno) is the etiological agent of francisellosis in cultured warm water fish, such as tilapia. Antibiotics are administered to treat the disease but a better understanding of Fno infection biology will inform improved treatment and prevention measures. However, studies with native hosts are costly and considerable benefits would derive from access to a practical alternative host. Here, larvae of Galleria mellonella were assessed for suitability to study Fno virulence. Results: Larvae were killed by Fno in a dose-dependent manner but the insects could be rescued from lethal doses of bacteria by antibiotic therapy. Infection progression was assessed by histopathology (haematoxylin and eosin staining, Gram Twort and immunohistochemistry) and enumeration of bacteria recovered from the larval haemolymph on selective agar. Fno was phagocytosed and could survive intracellularly, which is consistent with observations in fish. Virulence of five Fno isolates showed strong agreement between G. mellonella and red Nile tilapia hosts.Conclusions: This study shows that an alternative host, G. mellonella, can be applied to understand Fno infections, which will assist efforts to identify solutions to piscine francisellosis thus securing the livelihoods of tilapia farmers worldwide and ensuring the production of this important food source.

Administration of dehydrated oxytetracycline effectively reduces francisellosis mortality in Nile tilapia

“…Recently, a study on the suitability of Galleria mellonella larva as an infection model for piscine francisellosis showed that early tetracycline treatment increases larval survival when infected with fish‐isolated F. orientalis (previously Francisella noatunensis subsp. orientalis ) (Djainal et al, 2020). However, the effectiveness of different OTC dosages at different stages of F. orientalis infection, and their effects on tilapia tissues, is poorly addressed in the literature.…”