A Silkworm Infection Model for In Vivo Study of Glycopeptide Antibiotics

Abstract

Glycopeptide antibiotics (GPAs) are drugs of last resort for treating infections by Gram-positive bacteria. They inhibit bacterial cell wall assembly by binding to the d-Ala-d-Ala terminus of peptidoglycan precursors, leading to cell lysis. Vancomycin and teicoplanin are first generation GPAs, while dalbavancin is one of the few, recently approved, second generation GPAs. In this paper, we developed an in vivo insect model to compare, for the first time, the efficacy of these three GPAs in curing Staphylococcus aureus infection. Differently from previous reports, Bombyx mori larvae were reared at 37 °C, and the course of infection was monitored, following not only larval survival, but also bacterial load in the insect body, hemocyte activity, phenoloxidase activity, and antimicrobial peptide expression. We demonstrated that the injection of S. aureus into the hemolymph of B. mori larvae led to a marked reduction of their survival rate within 24–48 h. GPAs were not toxic to the larvae and cured S. aureus infection. Dalbavancin was more effective than first generation GPAs. Due to its great advantages (i.e., easy and safe handling, low rearing costs, low antibiotic amount needed for the tests, no restrictions imposed by ethical and regulatory issues), this silkworm infection model could be introduced in preclinical phases—prior to the use of mice—accelerating the discovery/development rate of novel GPAs.

Galleria mellonella: The Versatile Host for Drug Discovery, In Vivo Toxicity Testing and Characterising Host-Pathogen Interactions

“…Insects possess a highly successful immune system that rapidly identifies pathogens and parasites and either kills them directly or immobilises them thus ensuring the survival of the host [ 1 ]. A wide range of structural and functional similarities exist between the insect immune response and the innate immune response of mammals [ 2 , 3 ] and, as a result, a wide variety of insects ( Galleria mellonella , Drosophila melanogaster , Manduca sexta , Bombyx mori ) is now used as in vivo models for assessing microbial virulence or for evaluating the in vivo efficacy and toxicity of antimicrobial compounds [ 4 , 5 , 6 , 7 ]. Larvae of the greater wax moth ( Galleria mellonella ) are widely used in academia and industry and in many cases generate results comparable to those that can be obtained using mammals [ 8 , 9 , 10 ].…”

The Silkworm as a Source of Natural Antimicrobial Preparations: Efficacy on Various Bacterial Strains

“…This lepidopteran has also assumed great importance as a bioreactor capable of producing specific proteins such as silky biomaterials and molecules with biological activity [ 31 ]; the latter application is becoming particularly important in relation to the problem of the spread of different bacterial strains resistant to conventional antibiotics, and therefore, the lepidopteran is becoming important for the consequent search for natural compounds with antimicrobial activity [ 32 ]. Moreover, B. mori could be used as an alternative animal model for preclinical studies regarding infections by pathogens and the effectiveness of antibiotic therapies [ 32 , 33 , 34 ].…”

Antimicrobial Activity of Nanoconjugated Glycopeptide Antibiotics and Their Effect on Staphylococcus aureus Biofilm

“…This is the case of the recent work of Chen et al (2019) , who reported the effect of IONPs carrying vancomycin on C. difficile in mice infection model, demonstrating that nanoconjugated vancomycin exerted a therapeutic effect higher than free vancomycin, reducing intestinal inflammation, facilitating mucosal viability, and limiting the antibiotic side effects on intestinal microbiota. Our next goal is to test NP-TEICO and NP-VANCO in the invertebrate infection model that we have recently developed for comparing GPA efficacy in curing in vivo infections ( Montali et al, 2020 ). We employed easy-to-handle larvae of the silkworm Bombyx mori infected by S. aureus .…”