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.

Identification and RNAi‐based functional analysis of chitinase family genes in Agrotis ipsilon

“…Based on RNAi phenotypes, the same section of ventral abdominal integument (the seventh body segment) was dissected from each sample. All samples were fixed in 4% paraformaldehyde at 4°C for at least 2 days to prepare paraffin sections, and stained with hematoxylin and eosin in accordance with the protocol described by Djainal et al 32 . The slides were observed under an OLYMPUS BX51 microscope (Olympus), and photographs were taken using an OLYMPUS digital camera.…”

The effect of a temperature‐sensitive prophage on the evolution of virulence in an opportunistic bacterial pathogen

“…We estimated the virulence of our S. marcescens strains by measuring the longevity of waxmoth larvae ( Galleria mellonella ) injected with 5 μl of bacterial culture. G. mellonella is a good model for bacterial virulence as it has been shown that virulence in this host is also a good proxy for virulence in vertebrate hosts such as mouse or fish (Djainal et al, 2020; Jander et al, 2000). We grew bacterial cultures of evolved strains overnight at 31°C in Bioscreen wells in 400 μl of SPL 1% inoculated with the strains frozen stocks using a cryoreplicator.…”

The effect of a temperature-sensitive prophage on the evolution of virulence in an opportunistic bacterial pathogen

“…We estimated the virulence of our S. marcescens strains by measuring the longevity of waxmoth larvae ( Galleria mellonella ) injected with 5 μl of bacterial culture. G. mellonella is an interesting model for bacterial virulence as it had been shown that virulence in this host is also a good proxy for virulence in vertebrate hosts such as mouse or fish (Jander et al, 2000; Djainal et al, 2020). We grew bacterial cultures of evolved strains overnight at 31 °C in Bioscreen wells in 400 μl of SPL 1 % inoculated with the strains frozen stocks using a cryoreplicator.…”