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Bombyx mori as a model for Niallia circulans pathogenicity
M Ismail Hossain1, Nusrat U A Saleh1, Al Numan1
1Department of Biochemistry and Microbiology, School of Health and Life Sciences, North South University, Dhaka, Bangladesh.
Abstract:
Increasing incidences of resistance to antibiotics by pathogenic bacteria is a worldwide concern and isolation of antibiotic-resistant strains of Niallia circulans (formerly known as Bacillus circulans), an opportunistic human pathogen, has been reported. Due to their lack of ethical constraints as well as their cost-effective rearing, invertebrates have been commonly used to study infection by bacteria pathogenic to humans. In this study, we demonstrate that a foodborne strain of N. circulans kills larvae of the silkworm, Bombyx mori within 48 h after hemolymph injection. The infected larvae turned black with an increase in the phenoloxidase (PO) activity in the hemolymph. Midgut injection of N. circulans resulted in the killing of larvae within 96 h. A significant increase in bacterial load was observed in the hemolymph 12 h after infection. The viable hemocyte number decreased to 48% within 12 h of injection. RT-qPCR analysis revealed that upon hemolymph infection with N. circulans the expression of the antimicrobial peptide (AMP) genes, Bmdefensin-B and Bmgloverin-3, were upregulated 2.5- and 1.8-fold, respectively, whereas 1.6-fold upregulation was observed for BmToll-2 in the larval fat body. Therapeutic effects of antibiotics like tetracycline, imipenem, ceftriaxone, ampicillin, and clindamycin were observed against N. circulans in the Bombyx larvae with varying efficacies. Results from this study suggest that larvae of B. mori can be used as infection models for screening therapeutics that are effective against N. circulans.
Insights
Niallia circulans, an opportunistic pathogen, kills Bombyx mori silkworm larvae. This study shows silkworms can model N. circulans infections and screen antibiotic effectiveness against this growing threat.
Area of Science:
- Microbiology
- Infectious Diseases
- Immunology
Background:
- Antibiotic resistance in pathogenic bacteria is a global health concern.
- Niallia circulans (formerly Bacillus circulans) is an opportunistic human pathogen with emerging antibiotic resistance.
- Invertebrates offer a cost-effective and ethically viable model for studying human bacterial infections.
Purpose of the Study:
- To investigate the pathogenicity of N. circulans in a Bombyx mori silkworm model.
- To assess the efficacy of various antibiotics against N. circulans infections in vivo.
- To evaluate the potential of B. mori larvae as a model for screening anti-N. circulans therapeutics.
Main Methods:
- Larval infection via hemolymph and midgut injection of N. circulans.
- Monitoring of larval mortality, melanization, and phenoloxidase (PO) activity.
- Quantification of bacterial load and hemocyte counts in hemolymph.
- Gene expression analysis (RT-qPCR) of antimicrobial peptide (AMP) and Toll pathway genes.
- In vivo antibiotic efficacy testing.
Main Results:
- N. circulans infection led to rapid mortality in B. mori larvae (within 48-96 hours).
- Infection caused melanization and increased hemolymph PO activity, with increased bacterial load and decreased hemocyte counts.
- Upregulation of AMP genes (Bmdefensin-B, Bmgloverin-3) and BmToll-2 observed in response to infection.
- Tested antibiotics (tetracycline, imipenem, ceftriaxone, ampicillin, clindamycin) showed varying therapeutic effects.
Conclusions:
- Bombyx mori larvae serve as a suitable and effective infection model for N. circulans.
- The silkworm model can be utilized for screening potential therapeutic agents against N. circulans.
- This research contributes to understanding host-pathogen interactions and developing strategies against antibiotic-resistant bacteria.
