Influence of Plasmid Type on the Replication of Rhodococcus equi in Host Macrophages.
Abstract: The soil-dwelling, saprophytic actinomycete is a multihost, facultative intracellular pathogen of macrophages. When inhaled by susceptible foals, it causes severe bronchopneumonia. It is also a pathogen of pigs, which may develop submaxillary lymphadenitis upon exposure. isolates obtained from foals and pigs possess conjugative plasmids housing a pathogenicity island (PAI) containing a novel family of genes of unknown function called the virulence-associated protein or family. The PAI regions of the equine and swine plasmids differ in gene composition, with equine isolates possessing six genes, including the major virulence determinant , while the PAIs of swine isolates house and five other unique genes. Possession of the pVAPA-type virulence plasmid by equine isolates bestows the capacity for intramacrophage replication essential for disease development . Swine isolates of are largely unstudied. Here, we show that isolates from pigs, carrying pVAPB-type plasmids, are able to replicate in a plasmid-dependent manner in macrophages obtained from a variety of species (murine, swine, and equine) and anatomical locations. Similarly, equine isolates carrying pVAPA-type plasmids are capable of replication in swine macrophages. Plasmid swapping between equine and swine strains through conjugation did not alter the intracellular replication capacity of the parental strain, indicating that coevolution of the plasmid and chromosome is not crucial for this attribute. These results demonstrate that while distinct plasmid types exist among isolates obtained from equine and swine sources, this tropism is not determined by host species-specific intramacrophage replication capabilities. This work greatly advances our understanding of the opportunistic pathogen , a disease agent of animals and immunocompromised people. Clinical isolates from diseased foals carry a conjugative virulence plasmid, pVAPA1037, that expresses Vap proteins, including VapA, essential for intramacrophage replication and virulence . The understudied isolates from pigs carry a related but different plasmid, pVAPB, expressing distinct Vap proteins, including VapB. In this work, we document for the first time that isolates carrying pVAPB-type plasmids are capable of intramacrophage replication. Moreover, we show that isolates carrying either plasmid type can replicate in both equine and swine macrophages, indicating that host species tropism is not due to species-specific intramacrophage replication capabilities defined by plasmid type. Furthermore, plasmid swapping between equine and swine strains did not alter intracellular replication capacity, indicating that coevolution of the plasmid and chromosome is not essential for intracellular growth.
Publication Date: 2016-10-12 PubMed ID: 27747295PubMed Central: PMC5061997DOI: 10.1128/mSphere.00186-16Google Scholar: Lookup
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Summary
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The research article demonstrates that the bacterium Rhodococcus equi, which can cause severe pneumonia in foals and lymphadenitis in pigs, is influenced by certain types of plasmids, which can affect its replication within its host’s macrophages. The study found that host-species tropism does not impact intracellular replication abilities, showing a novel insight into this pathogen.
Understanding Rhodococcus equi and Plasmid types
- The bacterium Rhodococcus equi is a pathogen found in the soil and can cause severe respiratory disease in foals and lymphadenitis in pigs.
- This bacterium possesses conjugative plasmids, which are DNA molecules that can replicate independently of chromosomal DNA.
- These plasmids contain a pathogenicity island (PAI) with a unique group of genes called the virulence-associated protein or Vap family.
- The study observes two types of plasmid – pVAPA-type in equine isolates and pVAPB-type in swine isolates. Each has its own characteristics and Vap genes composition.
Differences between Equine and Swine Isolates
- The PAI regions of equine and swine plasmids vary significantly in their Vap gene composition.
- Equine isolates contain the pVAPA-type plasmid, which has six Vap genes, including VapA, a major factor for virulence and intracellular replication.
- Swine isolates carry the pVAPB-type plasmid, which has VapB and five other specific Vap genes.
Key Findings and Implications
- The swine isolates can replicate in a plasmid-dependent way within macrophages obtained from different species (i.e., mouse, pig, and horse) and anatomical locations.
- Similarly, equine isolates carrying pVAPA-type plasmids can replicate in swine macrophages.
- The swapping of plasmids through conjugation between equine and swine isolates does not affect the parental strain’s intracellular replication ability, suggesting coevolution of the plasmid and chromosome is not a requirement for this capability.
- The study emphasizes that distinct plasmid types exist among Rhodococcus equi isolates obtained from horses and pigs, but host species does not dictate this diversity.
- This contributes to our understanding of Rhodococcus equi, an opportunistic pathogen affecting animals and immunocompromised people.
Cite This Article
APA
Willingham-Lane JM, Berghaus LJ, Giguère S, Hondalus MK.
(2016).
Influence of Plasmid Type on the Replication of Rhodococcus equi in Host Macrophages.
mSphere, 1(5), e00186-16.
https://doi.org/10.1128/mSphere.00186-16 Publication
Researcher Affiliations
- Department of Infectious Disease, University of Georgia, Athens, Georgia, USA.
- Department of Large Animal Medicine, University of Georgia, Athens, Georgia, USA.
- Department of Large Animal Medicine, University of Georgia, Athens, Georgia, USA.
- Department of Infectious Disease, University of Georgia, Athens, Georgia, USA.
Grant Funding
- R01 AI060469 / NIAID NIH HHS
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