Analysis of Shigella flexneri-mediated infections in model organism Caenorhabditis elegans

Abstract

Background: Shigella flexneri is the causative agent of bacillary dysentery and generates a significant global disease burden. The aim of this study was to analyze the pathogenesis and host immune response, at both the physiological and molecular level, using the model organism Caenorhabditis elegans, in response to S. flexneri. C. elegans is a nematode that responds to infection with a simple innate immune system, key aspects of which have been shown to be conserved. Methods: S. flexneri-mediated infection of C. elegans was performed in both solid and liquid assays. The expression and subsequent regulation of host candidate antimicrobial genes such as lysozymes, C-type lectins and pathogen virulence genes were kinetically analyzed in the S. flexneri-exposed nematode. Results: In solid assays, worms fed with S. flexneri showed complete killing at 153 ± 9 h. The kinetic studies showed that S. flexneri killed the worms upon continuous exposure at 41 ± 1.7 h. However, short-time exposure of the host to S. flexneri indicated that 14 h of exposure resulted in a loss of progeny, and death occurred after 46 h. Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that mRNA levels of host candidate antimicrobial genes and pathogen virulence genes varied significantly at the time of early infection. Conclusions: The killing of C. elegans requires live bacteria, and a minimal exposure time is sufficient for S. flexneri to have a lethal effect. The candidate antimicrobial genes and virulence genes are kinetically regulated within C. elegans during S. flexneri-mediated infections, thereby exhibiting their role and contribution in the host innate immune system.

Keywords::

• Caenorhabditis elegans
• Shigella
• pathogenesis
• innate immunity
• gene expression

Acknowledgements

We thank the Caenorhabditis Genetics Center, which is funded by the National Institutes of Health, National Center for Research Resources, for providing C. elegans N2 wild-type strain and E. coli OP50. This work was supported in part by grants from the Department of Biotechnology (DBT), Ministry of Science and Technology and the University Grants Commission (UGC), India. Authors also gratefully acknowledge the use of the Bioinformatics Infrastructure Facility, Alagappa University, funded by DBT, Ministry of Science and Technology, Government of India (No. BT/BI/04/055/2001).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.