#FEMSmicroBlog: Using silkworms to study pathogenic bacteria

29-07-2022

The National Moth Week celebrates the beauty, life cycles and habitats of moths. Bombyx mori, the domesticated silkworm, is a major insect model used for research as a more ethical option compared to mammal models. Nusrat Uddin Abu Saleh explains for the #FEMSmicroBlog why many pathogen infection trials involving mammals could be substituted with insects – and especially with lower animals such as silkworms. #MicrobiologyEvents

 

Insects as an ethical alternative to mammals

Animal models are commonly utilized in life sciences and other fields to gain a complete understanding of specific scientific questions. For these experiments, many researchers rely on higher organisms, such as mice.

However, using mammals may create challenges that involve animal rights, bioethical issues, etc. As a result, selecting a suitable model animal to avoid using mammals has become an issue in current life science research. This is why researchers acknowledge and suggest insects as suitable alternatives to mammals.

One order of insects that is commonly used in research contains the lepidopteran including butterflies and moths. Here, research relies on the worms or larvae of adult moths as they are generally easier to handle and can be injected with microbes or agents of interest.

Insect larvae are easy to handle and can be injected with agents of interest making them useful for research studies.

 

Studying human diseases in silkworms

Bombyx mori, the domestic silk moth, was the first lepidopteran for which draft genome sequences became available in 2004. Genomic studies showed that some silkworm genes are highly homologous to certain genes related to human hereditary diseases. Therefore, the silkworm could provide a candidate model for studying human diseases.

For example, the adenylate protein kinase signaling pathway plays an important role in the regulation of human blood glucose. Interestingly, this signaling pathway also regulates the glucose concentration in the hemolymph – the blood – of the silkworm while the gene for the insulin-like peptide of the silkworm has about 40% similarity to the gene for human insulin.

Based on this, researchers established a silkworm diabetes model by expressing the human insulin receptor in transgenic silkworms. Administering human insulin to these transgenic silkworms reduced the hemolymph glucose levels and activated adenylate protein kinase signaling in the fat body. This study used “humanized” silkworms as a potential novel strategy for in vivo drug evaluation in animal models.

 

Silkworms as infection models

Bombyx larvae have also many advantageous features for their use as infection models. For example, ethical constraints are missing; reproduction procedures are cost-effective; larger volumes can be accurately injected into the hemolymph or midgut and isolated organs are useful for pharmacological studies.

Immunological studies showed that insects apparently lack an adaptive immunity. Yet, the immune responses of insects and mammals are remarkably similar. Hemocytes in the hemolymph of insects function as immune cells and recognize and phagocytose pathogens. They even kill the ingested microbes with superoxide similarly to how neutrophils attack pathogens in the human body.

Additionally, lots of research relies on silkworms to study fungal pathogenicity and to identify bacterial exotoxins. At the same time, many microbiologists investigate the therapeutic effects of antibiotics in silkworms.

Silkworm larvae after infections with the pathogen Klebsiella pneumoniae.
K. pneumoniae-infected B. mori larvae. From Tuba et al. (2021).

For example, administering well-known antibiotics into the hemolymph of silkworm larvae resulted in the protection against the enterohemorrhagic Escherichia coli O157:H7. Another study even identified effective antibiotics against multidrug-resistant strains of K. pneumoniae based on rapid screening.

In conclusion, animal welfare concerns have compelled scientists to restrict the number of vertebrates – especially mammals such as mice – to be used in experimentation in recent years. Silkworms have been important players in the silk industry for ages without any special approval. Hence, using them as experimental animal models may be the way to set the ultimate example for ethical experimentation.

 

About the author of this blog

Nusrat Uddin Abu Saleh graduated from North South University (Dhaka, Bangladesh) with a Bachelor of Science in Biochemistry and Biotechnology in August 2019. She has recently completed a Masters in Biotechnology from the same organization and plans to pursue PhD abroad this year. In addition to her interest in microbiology, Nusrat is also interested in cancer biology and wants to research how gut microbiota influences cancer progression.

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The section #MicrobiologyEvents for the #FEMSmicroBlog reports about events and meetings relevant to our network. These include world awareness days, FEMS-sponsored meetings or meetings of Member Societies and many more.

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