Quantitative Evaluation of the Therapeutic Effects of Antibiotics Using Silkworms Infected with Human Pathogenic Microorganisms

Abstract

The injection of bacteria (Staphylococcus aureus, Stenotrophomonas maltophilia) or true fungi (Candida albicans, Candida tropicalis) that are pathogenic to humans into the silkworm hemolymph leads to death of the larvae within 2 days. Antibiotics used for clinical purposes have therapeutic effects on silkworms infected with these pathogens. The 50% effective doses obtained by injection into the silkworm hemolymph are consistent with those reported for mice. Injection of vancomycin and kanamycin into the silkworm hemolymph was effective, but oral administration was not. Chloramphenicol, which is effective by oral administration, appeared in the silkworm hemolymph soon after injection into the midgut, whereas vancomycin did not. Isolated midgut membranes were impermeable to vancomycin. Thus, the ineffectiveness of oral administration of vancomycin to silkworms is due to a lack of intestinal absorption.

Nosokomycins, new antibiotics discovered in an in vivo-mimic infection model using silkworm larvae. I: Fermentation, isolation and biological properties

“…Fertilized silkworm eggs of Bombyx mori (HuÁYo TukubaÁNe) were purchased from Ehime Sansyu, Ehime, Japan. 4,5 Hatched larvae were raised by feeding them with an artificial diet (Silk Mate 2S, Nihon Nosan Kogyo, Kanagawa, Japan) in an incubator at 27 1C until they had developed into forth-molted larva. On the first day of fifth-instar larvae, the silkworms were fed for 1 day with an antibiotic-free artificial diet (Silk Mate, Katakura Industries, Saitama, Japan).…”

“…Furthermore, it is very difficult to use such in vivo models as a primary screening system for the discovery of new antibiotics. Recently, a number of researchers have focused on nonmammalian animals such as zebrafish, 1 Caenorhabditis elegans, 2 Drosophila melanogaster 3 and silkworms [4][5][6] as alternative in vivo models. Sekimizu et al 4,5 proposed an alternative method using silkworm larvae (silkworm assay) for evaluating the in vivo efficacy of antibiotics.…”

“…Recently, a number of researchers have focused on nonmammalian animals such as zebrafish, 1 Caenorhabditis elegans, 2 Drosophila melanogaster 3 and silkworms [4][5][6] as alternative in vivo models. Sekimizu et al 4,5 proposed an alternative method using silkworm larvae (silkworm assay) for evaluating the in vivo efficacy of antibiotics. In this silkworm assay, when silkworm larvae were infected with various human pathogenic microorganisms, including methicillin-resistant Staphylococcus aureus (MRSA), they died within several days of infection.…”

“…On the other hand, when clinically used antibiotics were injected into such infected larvae, they survived, indicating that the efficacy of various antibiotics can be evaluated by this method. 4,5 These findings prompted us to incorporate the silkworm assay as a tool for the screening of microbial culture broths for anti-MRSA antibiotics. We predicted that new antibiotics that are effective in in vivo systems would be more efficiently discovered by the silkworm assay than by the agar diffusion assay using paper disks.…”

Use of Galleria mellonella larvae to evaluate the in vivo anti-fungal activity of [Ag2(mal)(phen)3]

“…Insect models of microbial infections have been employed to investigate the anti-microbial properties of drugs (Mahajan-Miklos et al 1999;Bernall and Kimbrell 2000;Lionakis and Kontoyiannis 2005) and offer many advantages over the use of mammals (Kavanagh and Reeves 2004). G. mellonella has also been used to evaluate the anti-fungal activity of amphotericin B, flucytosine and fluconazole in an insect model of C. neoformans infection (Mylonakis et al 2005) while silkworms have also been used to investigate the activity of commonly used antibiotics including the antifungal fluconazole (Hamamoto et al 2004). …”