Temperature and Oxidative Stress as Triggers for Virulence Gene Expression in Pathogenic Leptospira spp.

Tricia Fraser,Paul D Brown

doi:10.3389/fmicb.2017.00783

Abstract

Leptospirosis is a zooanthroponosis aetiologically caused by pathogenic bacteria belonging to the genus, Leptospira. Environmental signals such as increases in temperatures or oxidative stress can trigger response regulatory modes of virulence genes during infection. This study sought to determine the effect of temperature and oxidative stress on virulence associated genes in highly passaged Leptospira borgpeterseneii Jules and L. interrogans Portlandvere. Bacteria were grown in EMJH at 30°C, 37°C, or at 30°C before being transferred to 37°C. A total of 14 virulence-associated genes (fliY, invA, lenA, ligB, lipL32, lipL36, lipL41, lipL45, loa22, lsa21, mce, ompL1, sph2, and tlyC) were assessed using endpoint PCR. Transcriptional analyses of lenA, lipL32, lipL41, loa22, sph2 were assessed by quantitative real-time RT-PCR at the temperature conditions. To assess oxidative stress, bacteria were exposed to H2O2 for 30 and 60 min with or without the temperature stress. All genes except ligB (for Portlandvere) and ligB and mce (for Jules) were detectable in the strains. Quantitatively, temperature stress resulted in significant changes in gene expression within species or between species. Temperature changes were more influential in gene expression for Jules, particularly at 30°C and upshift conditions; at 37°C, expression levels were higher for Portlandvere. However, compared to Jules, where temperature was influential in two of five genes, temperature was an essential element in four of five genes in Portlandvere exposed to oxidative stress. At both low and high oxidative stress levels, the interplay between genetic predisposition (larger genome size) and temperature was biased towards Portlandvere particularly at 30°C and upshift conditions. While it is clear that expression of many virulence genes in highly passaged strains of Leptospira are attenuated or lost, genetic predisposition, changes in growth temperature and/or oxidative intensity and/or duration were factors which acted in isolation or together with other regulatory cues to contribute to the variable gene expression observed in this study. Overall, differential gene expression in serovar Portlandvere was more responsive to temperature and oxidative stress.

Highlights

Leptospirosis is a zooanthroponosis, widely distributed throughout the world and aetiologically caused by pathogenic bacteria belonging to the genus, Leptospira (Bharti et al, 2003; Pappas et al, 2008)
Gene Expression of Virulence-Associated Genes in L. borgpetersenii Jules and L. interrogans Portlandvere Exposed to Temperature Stress Conditions
The transmission cycle of pathogenic Leptospira species necessitates the ability to respond to environmental changes and is supported by altered gene expression of leptospiral exoproteins predominantly involved in motility, signal transduction and energy-generating functions during infection (Matsui et al, 2012; Eshghi et al, 2015)

Summary

Introduction

Leptospirosis is a zooanthroponosis, widely distributed throughout the world and aetiologically caused by pathogenic bacteria belonging to the genus, Leptospira (Bharti et al, 2003; Pappas et al, 2008). Pathogenic Leptospira species are invasive and infection results from their ability to colonize and invade the renal tubes of incidental hosts. Pathogenicity is multifactorial, requiring integrated mechanisms and pathways to establish an infection. As diverse pathogenic bacteria share common strategies to cause disease and infection, the extent of damage to host tissue is determined by multiple gene or gene products involved in pathways of signal transduction, invasiveness and toxigenesis. The changing environment, often influenced by climate change, prompts adaptation, and regulatory responses to enhance the survival of the pathogen, and by extension, the ability to cause infection is largely due to the pathogen’s ability and adaptability (Reis et al, 2008; Lau et al, 2010; Batchelor et al, 2012)

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