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Nieto V, Kroken AR, Grosser MR, Smith BE, Metruccio MME, Hagan P, Hallsten ME, Evans DJ, Fleiszig SMJ. Type IV Pili Can Mediate Bacterial Motility within Epithelial Cells. mBio 2019; 10:e02880-18. [PMID: 31431558 PMCID: PMC6703432 DOI: 10.1128/mbio.02880-18] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 07/31/2019] [Indexed: 02/07/2023] Open
Abstract
Pseudomonas aeruginosa is among bacterial pathogens capable of twitching motility, a form of surface-associated movement dependent on type IV pili (T4P). Previously, we showed that T4P and twitching were required for P. aeruginosa to cause disease in a murine model of corneal infection, to traverse human corneal epithelial multilayers, and to efficiently exit invaded epithelial cells. Here, we used live wide-field fluorescent imaging combined with quantitative image analysis to explore how twitching contributes to epithelial cell egress. Results using time-lapse imaging of cells infected with wild-type PAO1 showed that cytoplasmic bacteria slowly disseminated throughout the cytosol at a median speed of >0.05 μm s-1 while dividing intracellularly. Similar results were obtained with flagellin (fliC) and flagellum assembly (flhA) mutants, thereby excluding swimming, swarming, and sliding as mechanisms. In contrast, pilA mutants (lacking T4P) and pilT mutants (twitching motility defective) appeared stationary and accumulated in expanding aggregates during intracellular division. Transmission electron microscopy confirmed that these mutants were not trapped within membrane-bound cytosolic compartments. For the wild type, dissemination in the cytosol was not prevented by the depolymerization of actin filaments using latrunculin A and/or the disruption of microtubules using nocodazole. Together, these findings illustrate a novel form of intracellular bacterial motility differing from previously described mechanisms in being directly driven by bacterial motility appendages (T4P) and not depending on polymerized host actin or microtubules.IMPORTANCE Host cell invasion can contribute to disease pathogenesis by the opportunistic pathogen Pseudomonas aeruginosa Previously, we showed that the type III secretion system (T3SS) of invasive P. aeruginosa strains modulates cell entry and subsequent escape from vacuolar trafficking to host lysosomes. However, we also showed that mutants lacking either type IV pili (T4P) or T4P-dependent twitching motility (i) were defective in traversing cell multilayers, (ii) caused less pathology in vivo, and (iii) had a reduced capacity to exit invaded cells. Here, we report that after vacuolar escape, intracellular P. aeruginosa can use T4P-dependent twitching motility to disseminate throughout the host cell cytoplasm. We further show that this strategy for intracellular dissemination does not depend on flagellin and resists both host actin and host microtubule disruption. This differs from mechanisms used by previously studied pathogens that utilize either host actin or microtubules for intracellular dissemination independently of microbe motility appendages.
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Affiliation(s)
- Vincent Nieto
- School of Optometry, University of California, Berkeley, California, USA
| | - Abby R Kroken
- School of Optometry, University of California, Berkeley, California, USA
| | - Melinda R Grosser
- School of Optometry, University of California, Berkeley, California, USA
| | - Benjamin E Smith
- Vision Science Program, University of California, Berkeley, California, USA
| | | | - Patrick Hagan
- Undergraduate Research Apprentice Program, University of California, Berkeley, California, USA
| | - Mary E Hallsten
- Undergraduate Research Apprentice Program, University of California, Berkeley, California, USA
| | - David J Evans
- School of Optometry, University of California, Berkeley, California, USA
- College of Pharmacy, Touro University California, Vallejo, California, USA
| | - Suzanne M J Fleiszig
- School of Optometry, University of California, Berkeley, California, USA
- Vision Science Program, University of California, Berkeley, California, USA
- Graduate Group in Microbiology, University of California, Berkeley, California, USA
- Graduate Group in Infectious Diseases and Immunity, University of California, Berkeley, California, USA
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