Comparative genomics of Rhodococcus equi virulence plasmids indicates host-driven evolution of the vap pathogenicity island

The conjugative virulence plasmid is a key component of the Rhodococcus equi accessory genome essential for pathogenesis. Three host-associated virulence plasmid types have been identified: the equine pVAPA and porcine pVAPB circular variants, and the linear pVAPN found in bovine (ruminant) isolates. We recently characterized the R. equi pangenome (Anastasi E, et al. 2016. Pangenome and phylogenomic analysis of the pathogenic actinobacterium Rhodococcus equi. Genome Biol Evol. 8:3140–3148.) and we report here the comparative analysis of the virulence plasmid genomes. Plasmids within each host-associated type were highly similar despite their diverse origins. Variation was accounted for by scattered single nucleotide polymorphisms and short nucleotide indels, while larger indels—mostly in the plasticity region near the vap pathogencity island (PAI)—defined plasmid genomic subtypes. Only one of the plasmids analyzed, of pVAPN type, was exceptionally divergent due to accumulation of indels in the housekeeping backbone. Each host-associated plasmid type carried a unique PAI differing in vap gene complement, suggesting animal host-specific evolution of the vap multigene family. Complete conservation of the vap PAI was observed within each host-associated plasmid type. Both diversity of host-associated plasmid types and clonality of specific chromosomal-plasmid genomic type combinations were observed within the same R. equi phylogenomic subclade. Our data indicate that the overall strong conservation of the R. equi host-associated virulence plasmids is the combined result of host-driven selection, lateral transfer between strains, and geographical spread due to international livestock exchanges

Listeria placental infection

The Gram-positive facultative intracellular bacterium Listeria monocytogenes is the causative agent of listeriosis, a severe food-borne infection. Pregnant women are at risk of contracting listeriosis, which can potentially lead to miscarriage, stillbirth, preterm birth, and congenital neonatal infections. While other systemic bacterial infections may result in adverse pregnancy outcomes at comparable frequencies, L. monocytogenes has particular notoriety because fetal complications largely occur in the absence of overt illness in the mother, delaying medical intervention. Here, we briefly review the pathophysiology and mechanisms of maternofetal listeriosis, discussed in light of a recent mBio report on Listeria transplacental infection in a nonhuman primate model

Comparative genomic analyses reveal a lack of a substantial signature of host adaptation in Rhodococcus equi (‘Prescottella equi’)

Rhodococcus equi (‘Prescottella equi’) is a pathogenic actinomycete primarily infecting horses but has emerged as an opportunistic human pathogen. We have sequenced the genome of the type strain of this species, R. equi strain C7T, and compared the genome with that of another foal isolate 103S and of a human isolate ATCC 33707. The R. equi strains are closely related to each other and yet distantly related to other rhodococci and Nocardia brasiliensis. The comparison of gene contents among R. equi strains revealed minor differences that could be associated with host adaptation from foals to humans, including the presence of a paa operon in the human isolate, which is potentially involved in pathogenesis

International spread of multidrug-resistant Rhodococcus equi

A multidrug-resistant clone of the animal and human pathogen Rhodococcus equi, MDR-RE 2287, has been circulating among equine farms in the United States since the 2000s. We report the detection of MDR-RE 2287 outside the United States. Our finding highlights the risk for MDR-RE spreading internationally with horse movements