Abstract
Pathogen host shifts represent a major source of new infectious diseases. There are several examples of cross-genus host jumps that have caused catastrophic epidemics in animal and plant species worldwide. Cross-kingdom jumps are rare, and are often associated with nosocomial infections. Here we provide an example of human-mediated cross-kingdom jumping of Exserohilum rostratum isolated from a patient who had received a corticosteroid injection and died of fungal meningitis in a Florida hospital in 2012. The clinical isolate of E. rostratum was compared with two plant pathogenic isolates of E. rostratum and an isolate of the closely related genus Bipolaris in terms of morphology, phylogeny, and pathogenicity on one C3 grass, Gulf annual rye grass (Lolium multiflorum), and two C4 grasses, Japanese stilt grass (Microstegium vimineum) and bahia grass (Paspalum notatum). Colony growth and color, as well as conidia shape and size were the same for the clinical and plant isolates of E. rostratum, while these characteristics differed slightly for the Bipolaris sp. isolate. The plant pathogenic and clinical isolates of E. rostratum were indistinguishable based on morphology and ITS and 28S rDNA sequence analysis. The clinical isolate was as pathogenic to all grass species tested as the plant pathogenic strains that were originally isolated from plant hosts. The clinical isolate induced more severe symptoms on stilt grass than on rye grass, while this was the reverse for the plant isolates of E. rostratum. The phylogenetic similarity between the clinical and plant-associated E. rostratum isolates and the ability of the clinical isolate to infect plants suggests that a plant pathogenic strain of E. rostratum contaminated the corticosteroid injection fluid and was able to cause systemic disease in the affected patient. This is the first proof that a clinical isolate of E. rostratum is also an effective plant pathogen.
Highlights
Several pathogenic microbes are capable of infecting a variety of organisms, belonging to different species, genera, families or even kingdoms
Examples of cross-kingdom jumps are those of the plant pathogenic bacterium Burkholderia cepacia to humans, causing cystic fibrosis [8], the plant endophyte Cryptococcus gattii from forest trees to animals and humans [9], and fungal plant pathogens such as Alternaria alternata, Aspergillus flavus, Fusarium oxysporum, Microascus cinereus and Rhizopus arrhizus to humans, causing invasive fungal infections, frequently with lethal outcomes [10]
Pathogen host shifts represent a major source of new infectious diseases that are a threat to the health of humans, animals or plants in certain areas [7]
Summary
Several pathogenic microbes are capable of infecting a variety of organisms, belonging to different species, genera, families or even kingdoms. Host jumps occurring at a cross-kingdom level are very rare, but can occur when a microbe normally colonizing a species from one taxonomic kingdom has the capacity to colonize a species belonging to another kingdom under special circumstances [4,5,6]. Of all human emerging infectious diseases that are of major public health concern, 73% are caused by zoonotic pathogens [5] Some of these pathogens have been shown to cycle through ecosystems from animal- to plant hosts and back, and to multiply on and in plants [11]. The infection strategies and epidemiology of these pathogens, whether considered primarily as plant, animal or human pathogens, are of particular interest from the perspectives of both the biology and evolution of crosskingdom pathogenesis [14]
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