Effective immunosuppression with dexamethasone phosphate in the Galleria mellonella larva infection model resulting in enhanced virulence of Escherichia coli and Klebsiella pneumoniae

Abstract

The aim was to evaluate whether immunosuppression with dexamethasone 21-phosphate could be applied to the Galleria mellonella in vivo infection model. Characterised clinical isolates of Escherichia coli or Klebsiella pneumoniae were employed, and G. mellonella larvae were infected with increasing doses of each strain to investigate virulence in vivo. Virulence was then compared with larvae exposed to increasing doses of dexamethasone 21-phosphate. The effect of dexamethasone 21-phosphate on larval haemocyte phagocytosis in vitro was determined via fluorescence microscopy and a burden assay measured the growth of infecting bacteria inside the larvae. Finally, the effect of dexamethasone 21-phosphate treatment on the efficacy of ceftazidime after infection was also noted. The pathogenicity of K. pneumoniae or E. coli in G. mellonella larvae was dependent on high inoculum numbers such that virulence could not be attributed specifically to infection by live bacteria but also to factors associated with dead cells. Thus, for these strains, G. mellonella larvae do not constitute an ideal infection model. Treatment of larvae with dexamethasone 21-phosphate enhanced the lethality induced by infection with E. coli or K. pneumoniae in a dose- and inoculum size-dependent manner. This correlated with proliferation of bacteria in the larvae that could be attributed to dexamethasone inhibiting haemocyte phagocytosis and acting as an immunosuppressant. Notably, prior exposure to dexamethasone 21-phosphate reduced the efficacy of ceftazidime in vivo. In conclusion, demonstration of an effective immunosuppressant regimen can improve the specificity and broaden the applications of the G. mellonella model to address key questions regarding infection.

Dual β-lactam combination therapy for multi-drug resistant Pseudomonas aeruginosa infection: enhanced efficacy in vivo and comparison with monotherapies of penicillin-binding protein inhibition

“…Unmanipulated controls were also included. Three larvae were randomly selected and injected with 75 µL Galleria saline 29 at 5, 20.5 and 24 hours post-infection and haemolymph was bled into individual sterile reaction tubes and 10 µL was loaded onto an improved Neubauer haemocytometer and the haemocytes counted with duplicates for each sample. This experiment was performed in triplicate to give n = 9 for each experimental condition.…”

An Update on Candida tropicalis Based on Basic and Clinical Approaches

“…Galleria mellonella larvae (Lepidoptera: Pyralidae) have been used as another invertebrate model to investigate fungal and host interactions (Champion et al, 2016 ), in systemic studies of antimicrobial efficiency (Wei et al, 2016 ), evaluation of virulence in immunosuppressive models (Torres et al, 2016 ), immunomodulatory response (Fuchs et al, 2016 ), and antifungal resistance (Souza et al, 2015 ).…”

Galleria mellonella experimental model for bat fungal pathogen Pseudogymnoascus destructans and human fungal pathogen Pseudogymnoascus pannorum

“…Galleria mellonella models have become invaluable to study cellular and humoral immune responses against pathogens [31–33], epigenetic influences on the evolution of virulence [32,34,35], and for development and testing antimicrobials [36–39]. It is relevant to add that the complete genomes of P. destructans and G. mellonella have become available recently [40,41].…”