Genomic loss in environmental and isogenic morphotype isolates of Burkholderia pseudomallei is associated with intracellular survival and plaque-forming efficiency.

Natnaree Saiprom,T Eoin West,Uriwan Surin,Wasun Chantratita,Sineenart Sengyee,Anucha Preechanukul,Narisara Chantratita,Sarunporn Tandhavanant,Ganjana Lertmemongkolchai,Tanes Sangsri,Rungnapa Phunpang,Apichai Tuanyok,Alfredo G Torres

doi:10.1371/journal.pntd.0008590

Abstract

BackgroundBurkholderia pseudomallei is an environmental bacterium that causes melioidosis. A facultative intracellular pathogen, B. pseudomallei can induce multinucleated giant cells (MNGCs) leading to plaque formation in vitro. B. pseudomallei can switch colony morphotypes under stress conditions. In addition, different isolates have been reported to have varying virulence in vivo, but genomic evolution and the relationship with plaque formation is poorly understood.Methodology/Principle findingsTo gain insights into genetic underpinnings of virulence of B. pseudomallei, we screened plaque formation of 52 clinical isolates and 11 environmental isolates as well as 4 isogenic morphotype isolates of B. pseudomallei strains K96243 (types II and III) and 153 (types II and III) from Thailand in A549 and HeLa cells. All isolates except one environmental strain (A4) and K96243 morphotype II were able to induce plaque formation in both cell lines. Intracellular growth assay and confocal microscopy analyses demonstrated that the two plaque-forming-defective isolates were also impaired in intracellular replication, actin polymerization and MNGC formation in infected cells. Whole genome sequencing analysis and PCR revealed that both isolates had a large genomic loss on the same region in chromosome 2, which included Bim cluster, T3SS-3 and T6SS-5 genes.Conclusions/SignificanceOur plaque screening and genomic studies revealed evidence of impairment in plaque formation in environmental isolates of B. pseudomallei that is associated with large genomic loss of genes important for intracellular multiplication and MNGC formation. These findings suggest that the genomic and phenotypic differences of environmental isolates may be associated with clinical infection.

Highlights

Burkholderia pseudomallei is a Gram-negative intracellular bacterium and the causative agent of melioidosis, a severe infectious disease in humans and animals
The fifty clinical isolates were obtained from 49 patients who were admitted with melioidosis at Nakhon Phanom Hospital
It is known that Bim cluster has a key function in actin polymerization which is required for intracellular movement of B. pseudomallei [24, 25] and T6SS-5 plays a major role for cell-to-cell fusion and intracellular spread [27, 29, 30]

Summary

Introduction

Burkholderia pseudomallei is a Gram-negative intracellular bacterium and the causative agent of melioidosis, a severe infectious disease in humans and animals. It is a biothreat Tier 1 select agent but widely spread in the environment in Southeast Asia, Thailand, and Northern Australia [1, 2]. Clinical isolates of B. pseudomallei appear to be genetically distinct from environmental strains, the bacterium in the environment is considered the major source of clinical infection [3,4,5]. The clinical features of melioidosis vary considerably, ranging from acute fulminant septicemia to chronic localized infection. Burkholderia pseudomallei is an environmental bacterium that causes melioidosis. Different isolates have been reported to have varying virulence in vivo, but genomic evolution and the relationship with plaque formation is poorly understood

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Conclusion