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A silkworm model of pathogenic bacterial infection
1Laboratory of Microbiology, Graduate School of Parmaceutical Sciences, The University of Tokyo, Tokyo, Japan.
Abstract:
Silkworms are invertebrate animals that are killed by bacteria pathogenic against humans, such as Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, and Vibrio cholerae. Injection into the hemolymph of antibiotics that are clinically used for human patients abolishes the killing effects. There are several advantages to using silkworms as an infection model, such as low cost, the absence of ethical problems that are associated with the use of mammals, and a body size large enough to handle while injecting sample solution into the hemolymph. We screened S. aureus mutants with attenuated virulence against silkworms and found three novel virulence regulatory genes, cvfA, cvfB, and cvfC. These genes contribute to virulence against mice and are required for exotoxin production. The cvfA gene is required for expression of the agr locus, which regulates most exotoxin genes, and a novel DNA binding protein SarZ. Silkworms are susceptible to S. aureus beta toxin, P. aeruginosa exotoxin A, and diphtheria toxin. Therefore, silkworms are a promising infection model animal for the identification and evaluation of virulenceassociated genes.
Insights
Silkworms offer a cost-effective, ethical infection model. Researchers identified three novel Staphylococcus aureus virulence genes (cvfA, cvfB, cvfC) crucial for exotoxin production and host defense.
Area of Science:
- Microbiology and Infectious Diseases
- Invertebrate Pathology
- Bacterial Virulence Mechanisms
Background:
- Silkworms are susceptible to human bacterial pathogens like Staphylococcus aureus.
- Antibiotic treatment in silkworms demonstrates their utility as a model for studying infection.
- Silkworms present advantages over mammalian models, including lower cost and ethical considerations.
Purpose of the Study:
- To identify novel virulence regulatory genes in Staphylococcus aureus using a silkworm infection model.
- To evaluate the role of identified genes in bacterial pathogenesis and exotoxin production.
- To establish silkworms as a viable model for assessing bacterial virulence factors.
Main Methods:
- Screening of Staphylococcus aureus mutants for attenuated virulence in silkworms.
- Infection assays involving injection of bacterial mutants into silkworm hemolymph.
- Analysis of gene expression and exotoxin production in identified mutants.
- Cross-validation of virulence gene function in a murine infection model.
Main Results:
- Three novel virulence regulatory genes (cvfA, cvfB, cvfC) were identified.
- These genes are essential for Staphylococcus aureus exotoxin production.
- cvfA regulates the agr locus, a key virulence gene cluster, and the novel DNA-binding protein SarZ.
- Silkworms demonstrated susceptibility to specific bacterial toxins, including beta toxin and exotoxin A.
Conclusions:
- Silkworms serve as a valuable and ethical model for studying bacterial infections and identifying virulence factors.
- The identified genes (cvfA, cvfB, cvfC) play a significant role in Staphylococcus aureus pathogenesis.
- This model facilitates the discovery and evaluation of virulence-associated genes and potential therapeutic targets.
