Population and functional genomic analysis of Lawsonia intracellularis
View/ Open
Date
29/06/2019Author
Bengtsson, Rebecca Ji
Metadata
Abstract
The Gram-negative, obligate intracellular bacterium Lawsonia intracellularis is the
aetiological agent of a non-zoonotic enteric disease known as proliferative
enteropathy (PE). PE has been detected in wide range of mammalian species,
including wild and domestic animals. The disease is most prevalent in pig herds where
it is endemic, with both subclinical and clinical infections. Porcine PE was first
described in 1931 and four different form of the disease are recognised, ranging from
mild to severe clinical manifestations. Over recent years rising outbreaks of equine
PE in foals have been reported and cross-species experimental infections have
demonstrated host-specificity for infection. Although the dynamics of L. intracellularis
infection have been examined, there is a lack of understanding population genetic
structure and the basis for pathogenesis due to difficulties with culturing obligate
intracellular organisms.
In this study, we developed a pipeline to obtain high quality whole genome sequences
of L. intracellularis through direct sequencing of clinical samples from field outbreaks
of porcine and equine PE, and cell passaged samples without the requirement of
cultivation, resulting in the generation of 25 draft genome assemblies. To explore the
genetic diversity of L. intracellularis, we performed comparative analysis which
revealed a clonal population structure among porcine derived isolates showing very
limited diversity, indicative of emergence from a recent clonal expansion. Our analysis
revealed that infections among different hosts are caused by genetically distinct
L. intracellularis sub-types. Finally, we focussed on a core gene encoding a putative
autotransporter, termed Lawsonia autotransporter B (latB), that exhibited genetic
variation in different strains, and immunofluorescent staining for LatB revealed the
putative autotransporter was expressed during infection and was associated with the
bacterial outer membrane.
Overall, these studies have provided insights into the genetic diversity and
evolutionary origin of L. intracellularis, enhancing our understanding of the population
biology of this important animal pathogen.