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Updated: Aug 14, 2025
Using a Bacterial Pathogen to Probe for Cellular and Organismic-level Host Responses
Published on: February 22, 2019
Specific preadaptations of Rhodococcus equi cooperate with its Virulence-associated protein A during macrophage
Thomas Haubenthal1, Philipp Hansen1, Ina Krämer1
1Institute for Cell Biology, University of Bonn, Bonn, Germany.
Abstract:
Gram-positive Rhodococcus equi (Prescotella equi) is a lung pathogen of foals and immunocompromised humans. Intra-macrophage multiplication requires production of the bacterial Virulence-associated protein A (VapA) which is released into the phagosome lumen. VapA pH-neutralizes intracellular compartments allowing R. equi to multiply in an atypical macrophage phagolysosome. Here, we show that VapA does not support intra-macrophage growth of several other bacterial species demonstrating that only few bacteria have the specific preadaptations needed to profit from VapA. We show that the closest relative of R. equi, environmental Rhodococcus defluvii (Prescotella defluvii), does not multiply in macrophages at 37°C even when VapA is present because of its thermosensitivity but it does so once the infection temperature is lowered providing rare experimental evidence for 'thermal restriction'. Using growth experiments with isolated macrophage lysosomes and modified infection schemes we provide evidence that R. equi resists the attack by phagolysosome contents at low pH for several hours. During this time, R. equi produces and secretes VapA which enables it to grow at the expense of lysosome constituents. We present arguments that, under natural infection conditions, R. equi is VapA-less during the initial encounter with the host. This has important implications for vaccine development.
Insights
Rhodococcus equi uses Virulence-associated protein A (VapA) to survive inside macrophages, but this protein is thermosensitive in related species. Understanding VapA
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Rhodococcus equi (Prescotella equi) is a Gram-positive lung pathogen affecting foals and immunocompromised humans.
- Intra-macrophage growth of R. equi depends on Virulence-associated protein A (VapA), which neutralizes phagosomal pH.
Purpose of the Study:
- To investigate the specificity of VapA's function in supporting intra-macrophage bacterial growth.
- To explore the role of temperature and host defenses in R. equi pathogenesis.
- To understand the implications of VapA's role in vaccine development.
Main Methods:
- In vitro growth experiments with various bacterial species and isolated macrophage lysosomes.
- Modified infection schemes to assess bacterial survival and multiplication under different conditions.
- Analysis of VapA production and secretion by R. equi during host-pathogen interaction.
Main Results:
- VapA specifically supports R. equi intra-macrophage growth; other bacteria do not benefit.
- Rhodococcus defluvii, a related species, fails to multiply at 37°C due to VapA thermosensitivity, but grows at lower temperatures, demonstrating 'thermal restriction'.
- R. equi survives low pH in lysosomes for hours, producing VapA to neutralize the environment and grow.
Conclusions:
- VapA is a key virulence factor for R. equi, enabling survival and multiplication within macrophages.
- Thermosensitivity of VapA in related species and 'thermal restriction' offer insights into host-pathogen specificity.
- R. equi may initially encounter the host without VapA, suggesting novel vaccine targets.
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