UMMS Affiliation

Department of Microbiology and Physiological Systems

Publication Date


Document Type



Bacterial Infections and Mycoses | Immunology and Infectious Disease | Microbiology


Salmonella invasion protein A (SipA) is a dual-function effector protein that plays roles in both actin polymerization and caspase-3 activation in intestinal epithelial cells. To date its function in other cell types has remained largely unknown despite its expression in multiple cell types and its extracellular secretion during infection. Here we show that in macrophages SipA induces increased caspase-3 activation early in infection. This activation required a threshold level of SipA linked to multiplicity of infection and may be a limiting factor controlling bacterial numbers in infected macrophages. In polymorphonuclear leukocytes, SipA or other Salmonella pathogenicity island 1 effectors had no effect on induction of caspase-3 activation either alone or in the presence of whole bacteria. Tagging of SipA with the small fluorescent phiLOV tag, which can pass through the type three secretion system, allowed visualization and quantification of caspase-3 activation by SipA-phiLOV in macrophages. Additionally, SipA-phiLOV activation of caspase-3 could be tracked in the intestine through multiphoton laser scanning microscopy in an ex vivo intestinal model. This allowed visualization of areas where the intestinal epithelium had been compromised and demonstrated the potential use of this fluorescent tag for in vivo tracking of individual effectors.


Salmonella, SipA, caspase-3, caspases, host-pathogen interactions, imaging, immune cells, microscopy

Rights and Permissions

Copyright © 2017 McIntosh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

DOI of Published Version



Infect Immun. 2017 Sep; 85(9): e00393-17. Published online 2017 Aug 18. Prepublished online 2017 Jun 19. doii:10.1128/IAI.00393-17. Link to article on publisher's site

Journal/Book/Conference Title

Infection and immunity

Related Resources

Link to Article in PubMed

PubMed ID


Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.



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