A Bombyx mori Infection Model for Screening Antibiotics against Staphylococcus epidermidis

Abstract

The increasing number of microorganisms that are resistant to antibiotics is prompting the development of new antimicrobial compounds and strategies to fight bacterial infections. The use of insects to screen and test new drugs is increasingly considered a promising tool to accelerate the discovery phase and limit the use of mammalians. In this study, we used for the first time the silkworm, Bombyx mori, as an in vivo infection model to test the efficacy of three glycopeptide antibiotics (GPAs), against the nosocomial pathogen Staphylococcus epidermidis. To reproduce the human physiological temperature, the bacterial infection was performed at 37 °C and it was monitored over time by evaluating the survival rate of the larvae, as well the response of immunological markers (i.e., activity of hemocytes, activation of the prophenoloxidase system, and lysozyme activity). All the three GPAs tested (vancomycin, teicoplanin, and dalbavancin) were effective in curing infected larvae, significantly reducing their mortality and blocking the activation of the immune system. These results corroborate the use of this silkworm infection model for the in vivo studies of antimicrobial molecules active against staphylococci.

Keywords: Bombyx mori; Staphylococcus epidermidis; antimicrobial compounds; dalbavancin; glycopeptide antibiotics; infection model; insect immune response; teicoplanin; vancomycin.

Figure 1

Survival rate of B. mori larvae injected with increasing CFU (colony forming unit) of S. epidermidis.

Figure 2

Survival rate. Curative efficacy of vancomycin (a), teicoplanin (b), and dalbavancin (c) (8.75 µg/g larval body weight) on larvae infected with S. epidermidis (1.05 × 10³ CFU). Results are from the same experiment run in parallel, using the same control groups (uninjected larvae and healthy larvae injected once or twice with saline solution) and infected larvae.

Figure 2

Survival rate. Curative efficacy of vancomycin (a), teicoplanin (b), and dalbavancin (c) (8.75 µg/g larval body weight) on larvae infected with S. epidermidis (1.05 × 10³ CFU). Results are from the same experiment run in parallel, using the same control groups (uninjected larvae and healthy larvae injected once or twice with saline solution) and infected larvae.

Figure 3

Hemocytes activity detected using a luminescence assay. Values represent mean ± s.e.m. Different letters indicate statistically significant differences among treatments (p < 0.05).

Figure 4

Analysis of proPO system activation. Values represent mean ± s.e.m. Different letters indicate statistically significant differences among treatments (p < 0.05).

Figure 5

Lysozyme relative activity. Values represent mean ± s.e.m. Different letters indicate statistically significant differences among treatments (p < 0.05).