title: Influence of Plasmid Type on the Replication ofRhodococcus equiin Host Macrophages.
abstract: The soil-dwelling, saprophytic actinomyceteRhodococcus equiis 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.R. equiisolates 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 orvapfamily. The PAI regions of the equine and swine plasmids differ invapgene composition, with equine isolates possessing sixvapgenes, including the major virulence determinantvapA, while the PAIs of swine isolates housevapBand five other uniquevapgenes. Possession of the pVAPA-type virulence plasmid by equine isolates bestows the capacity for intramacrophage replication essential for disease developmentin vivo. Swine isolates ofR. equiare largely unstudied. Here, we show thatR. equiisolates 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 amongR. equiisolates obtained from equine and swine sources, this tropism is not determined by host species-specific intramacrophage replication capabilities.IMPORTANCEThis work greatly advances our understanding of the opportunistic pathogenRhodococcus equi, 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 virulencein vivo. The understudiedR. equiisolates from pigs carry a related but different plasmid, pVAPB, expressing distinct Vap proteins, including VapB. In this work, we document for the first time thatR. equiisolates carrying pVAPB-type plasmids are capable of intramacrophage replication. Moreover, we show thatR. equiisolates 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.
authors.affiliation: Department of Infectious Disease, University of Georgia, Athens, Georgia, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Willingham-Lane
authors.affiliation: Department of Large Animal Medicine, University of Georgia, Athens, Georgia, USA.
authors.forename: Londa J
authors.initials: LJ
authors.lastname: Berghaus
authors.affiliation: Department of Large Animal Medicine, University of Georgia, Athens, Georgia, USA.
authors.forename: Steeve
authors.initials: S
authors.lastname: Giguère
authors.affiliation: Department of Infectious Disease, University of Georgia, Athens, Georgia, USA.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Hondalus
keywords: Rhodococcus equi; macrophage; species tropism; vap