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Identification and methods for prevention of Enterococcus mundtii infection in silkworm larvae, Bombyx mori, reared
Don Daniel Nwibo1, Yasuhiko Matsumoto, Kazuhisa Sekimizu
1Laboratory of Microbiology, Graduate School of Pharmaceutical Sciences, The University of Tokyo.
Abstract:
Previously, it was reported that Enterococcus mundtii (E. mundtii) was associated with flacherie disease of silkworm larvae reared on artificial diet. In this study, we report that E. mundtii was isolated from diseased silkworm larvae, and validated as a pathogenic bacterium of the animal. When silkworm larva was infected with 1.04 × 10⁶ colony-forming units of E. mundtii via oral administration of diet, half population died within six days, indicating that the bacterium is pathogenic to silkworm. Less severe infection was found to cause anorexia and hamper the development of larvae. This pathogen was found to proliferate in both time- and dose-dependent manner in the gastrointestinal tract of the animal. The bacterium was isolated from powder of artificial diet made from mulberry leaves, and from mulberry leaves growing at a field. Minimum inhibitory concentration determination revealed that this bacterium was susceptible to tested antibiotics. Vancomycin treatment of diet significantly decreased the number of E. mundtii in intestine of silkworm larvae infected with the bacteria, compared to control. Furthermore, autoclaving or gamma ray irradiation of diet was also effective for exclusion of E. mundtii from the diet without the loss of its nutrient capacities. These results suggest that mulberry leaves used in making artificial diet for silkworm larvae is one of the sources of E. mundtii infection; and that antibiotic treatment, autoclaving or gamma ray irradiation of artificial diet can exclude the bacteria.
Insights
Enterococcus mundtii causes flacherie disease in silkworms. Mulberry leaves in artificial diets are a source, but antibiotic treatment and diet sterilization methods like autoclaving can prevent infection.
Area of Science:
- Sericulture
- Animal Pathology
- Microbiology
Background:
- Enterococcus mundtii (E. mundtii) has been previously linked to flacherie disease in silkworms fed artificial diets.
- This study aimed to confirm the pathogenicity of E. mundtii in silkworms.
Purpose of the Study:
- To validate Enterococcus mundtii as a silkworm pathogen.
- To identify sources of E. mundtii infection in silkworm rearing.
- To evaluate methods for controlling E. mundtii in artificial diets.
Main Methods:
- Oral inoculation of silkworm larvae with E. mundtii.
- Isolation and quantification of bacteria in the silkworm gastrointestinal tract.
- Minimum inhibitory concentration (MIC) testing for antibiotics.
- Assessment of diet treatment methods (antibiotics, autoclaving, gamma irradiation).
Main Results:
- E. mundtii infection led to significant mortality (50% within six days) and developmental issues in silkworms.
- Bacterial proliferation occurred in a time- and dose-dependent manner within the silkworm gut.
- E. mundtii was isolated from artificial diet components (mulberry leaves) and field-grown mulberry leaves.
- Vancomycin treatment, autoclaving, and gamma irradiation effectively reduced E. mundtii in the diet and silkworm intestines.
Conclusions:
- Mulberry leaves used in artificial diets are a potential source of E. mundtii.
- Antibiotic treatment and sterilization of artificial diets are effective strategies to control E. mundtii infections in silkworms.
- E. mundtii is confirmed as a pathogenic bacterium affecting silkworm health and development.
