Defective phagocyte association during infection of Galleria mellonella with Yersinia pseudotuberculosis is detrimental to both insect host and microbe

Abstract

Adhesins facilitate bacterial colonization and invasion of host tissues and are considered virulence factors, but their impact on immune-mediated damage as a driver of pathogenesis remains unclear. Yersinia pseudotuberculosis encodes for a m ultivalent a dhesion m olecule (MAM), a mammalian cell entry (MCE) family protein and adhesin. MAMs are widespread in Gram-negative bacteria and enable enteric bacteria to colonize epithelial tissues. Their role in bacterial interactions with the host innate immune system and contribution to pathogenicity remains unclear. Here, we investigated how Y. pseudotuberculosis MAM contributes to pathogenesis during infection of the Galleria mellonella insect model. We show that Y. pseudotuberculosis MAM is required for efficient bacterial binding and uptake by hemocytes, the host phagocytes. Y. pseudotuberculosis interactions with insect and mammalian phagocytes are determined by bacterial and host factors. Loss of MAM, and deficient microbe–phagocyte interaction, increased pathogenesis in G. mellonella . Diminished phagocyte association also led to increased bacterial clearance. Furthermore, Y. pseudotuberculosis that failed to engage phagocytes hyperactivated humoral immune responses, most notably melanin production. Despite clearing the pathogen, excessive melanization also increased phagocyte death and host mortality. Our findings provide a basis for further studies investigating how microbe- and host-factors integrate to drive pathogenesis in a tractable experimental system.

Establishing an invertebrate Galleria mellonella greater wax moth larval model of Neisseria gonorrhoeae infection

“…It is also possible that the priming event engages the innate response of the resident larval population of hemocytes, which are then unavailable to potentially control subsequent infection. Many studies have demonstrated the binding of bacterial pathogens to larval hemocytes and their subsequent uptake, for example recent studies with Yersinia pseudotuberculosis [69], Salmonella Enteritidis [70] and Coxiella burnetti [71]. In preliminary confocal experiments we did see an association of gonococci with hemocytes in extracted hemolymph (data not shown), but more detailed studies are necessary to examine these bacterial-larval innate cell interactions, and are outside the scope of the current manuscript.…”

Immune-modulatory effects of low dose γ-radiation on wax moth (Galleria mellonella) larvae

“…This corroborates a previous study where G. mellonella larvae exposed to 100 – 400 Gy γ-radiation had altered haemocyte morphology, with cytoplasmic vacuolisation and distended mitochondria, as observed in transmission electron micrographs (El-Kholy et al, 2010). In insects, in an open body cavity, overproduction of melanin in response to a microbial infection can become highly toxic, and therefore there are trade-offs between front-loading with melanin and the clearance of pathogens (Lim et al, 2018; Krachler et al, 2021; Smith et al, 2021). Furthermore, any chemical or stressor that reduces melanin allows pathogens to proliferate and cause infection.…”

“…The cellular component comprises a heterogenous population of circulating haemocytes that are highly similar to human and mouse neutrophil/macrophage counterparts (Browne et al 2013). They play a critical role in pathogen phagocytosis, encapsulation, nodulation, degranulation, etosis, and hemostatic events (Kay et al 2019; Krachler et al, 2021). The humoral defences are comprised of the soluble immune factors of the haemolymph, which includes activation of the pro-phenoloxidase cascade, production of the antimicrobial pigment melanin and the darkening of the larval integument (Tsai et al 2016; Whitten and Coates, 2017).…”

Effect of acute ultraviolet radiation onGalleria mellonellahealth and immunity

“…The copyright holder for this preprint this version posted December 2, 2022. ; https://doi.org/10.1101/2022.12.02.517514 doi: bioRxiv preprint Kay et al 2019;Krachler et al, 2021;Lim et al, 2022). Therefore, while more haemocytes remain in larvae exposed to UVA, they were functionally compromised, whereas UVBradiated larvae had fewer haemocytes which was also compromised -which UVB is more potent an antagonist -as reflected in larval health, and expedited mortality when infected, in addition to compromised haemocyte functionality.…”