Outer Membrane Lipoprotein Lip40 Modulates Adherence, Colonization, and Virulence of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae FliY and YdjN are involved in cysteine/cystine utilization, oxidative resistance, and biofilm formation but are not determinants of virulence

Introduction

Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is a member of Actinobacillus in family Pasteurellaceae. It is the causative agent of porcine pleuropneumonia, which has caused huge economic losses to pig industry over the world. Cysteine is a precursor of many important biomolecules and defense compounds in the cell. However, molecular mechanisms of cysteine transport in A. pleuropneumoniae are unclear.

Methods

In this study, gene-deleted mutants were generated and investigated, to reveal the roles of potential cysteine/cystine transport proteins FliY and YdjN of A. pleuropneumoniae.

Results

Our results indicated that the growth of A. pleuropneumoniae was not affected after fliY or ydjN single gene deletion, but absence of both FliY and YdjN decreased the growth ability significantly, when cultured in the chemically defined medium (CDM) supplemented with cysteine or cystine as the only sulfur source. A. pleuropneumoniae double deletion mutant ΔfliYΔydjN showed increased sensitivity to oxidative stress. Besides, trans-complementation of YdjN into ΔfliYΔydjN and wild type leads to increased biofilm formation in CDM. However, the virulence of ΔfliYΔydjN was not attenuated in mice or pigs.

Discussion

These findings suggest that A. pleuropneumoniae FliY and YdjN are involved in the cysteine/cystine acquisition, oxidative tolerance, and biofilm formation, but not contribute to the pathogenicity of A. pleuropneumoniae.

The Metabolic Adaptation in Response to Nitrate Is Critical for Actinobacillus pleuropneumoniae Growth and Pathogenicity under the Regulation of NarQ/P

Nitrate metabolism is an adaptation mechanism used by many bacteria for survival in anaerobic environments. As a by-product of inflammation, nitrate is used by the intestinal bacterial pathogens to enable gut infection. However, the responses of bacterial respiratory pathogens to nitrate are less well understood. Actinobacillus pleuropneumoniae is an important bacterial respiratory pathogen of swine. Previous studies have suggested that adaptation of A. pleuropneumoniae to anaerobiosis is important for infection. In this work, A. pleuropneumoniae growth and pathogenesis in response to the nitrate were investigated. Nitrate significantly promoted A. pleuropneumoniae growth under anaerobic conditions in vitro and lethality in mice. By using narQ and narP deletion mutants and single-residue-mutated complementary strains of ΔnarQ, the two-component system NarQ/P was confirmed to be critical for nitrate-induced growth, with Arg50 in NarQ as an essential functional residue. Transcriptome analysis showed that nitrate upregulated multiple energy-generating pathways, including nitrate metabolism, mannose and pentose metabolism, and glycerolipid metabolism via the regulation of NarQ/P. Furthermore, narQ, narP, and its target gene encoding the nitrate reductase Nap contributed to the pathogenicity of A. pleuropneumoniae. The Nap inhibitor tungstate significantly reduced the survival of A. pleuropneumoniae in vivo, suggesting that Nap is a potential drug target. These results give new insights into how the respiratory pathogen A. pleuropneumoniae utilizes the alternative electron acceptor nitrate to overcome the hypoxia microenvironment, which can occur in the inflammatory or necrotic infected tissues.

HtrA of Actinobacillus pleuropneumoniae is a virulence factor that confers resistance to heat shock and oxidative stress

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, which is a severe and often fatal disease that results in significant economic loss. The means by which A. pleuropneumoniae survives within the host are not clear. High temperature requirement A (HtrA) proteases have been shown to affect cell viability during stressful conditions and are virulence factors in many bacterial species. In this study, we examined the biological role of HtrA during A. pleuropneumoniae infection by analyzing the impact of htrA mutation on virulence-associated phenotypes. We found that htrA mutation had a dramatic impact on stress tolerance. The htrA mutant (ΔhtrA) displayed a lethal phenotype at elevated temperature (42°C). Further, ΔhtrA exhibited increased susceptibility to H₂O₂-induced oxidative stress when compared to the parental strain (SLW01) and a complementation strain (ΔhtrA-Compl). Animal infection assays demonstrated that absence of HtrA led to decreased in vivo colonization ability, and ΔhtrA is less virulent in pigs relative to SLW01. Furthermore, pig competitive infection assays demonstrated fewer blood associated CFUs with ΔhtrA infection than with SLW01. These results demonstrate HtrA plays a significant role in the survival and growth of A. pleuropneumoniae during stressful conditions, and that immune escape and invasiveness are important to the process of A. pleuropneumoniae infection.

Involvement of the Actinobacillus pleuropneumoniae ompW Gene in Confrontation of Environmental Pressure

Actinobacillus pleuropneumoniae causes porcine pleuropneumonia. The function of the outer membrane protein W gene (ompW) of A. pleuropneumoniae has not been evaluated. Thus a deletion mutant of ompW, ΔompW, was constructed to explore the effect of ompW gene deletion on bacterial growth, biofilm formation, bacterial morphology, oxidative tolerance, susceptibility to antibiotics, and the expression of ribosome synthesis and ABC transporter related genes. Results showed that the ompW gene deletion did not affect biofilm formation and the growth of A. pleuropneumoniae but did affect bacterial morphology during steady growth, oxidative tolerance, and bacterial susceptibility to polymyxin B, kanamycin, and penicillin. The ompW gene deletion also affected the expression of ribosome synthesis and ABC transporter related genes. These results suggested that ompW may regulate the biological phenotype of A. pleuropneumoniae.

Actinobacillus pleuropneumoniae: The molecular determinants of virulence and pathogenesis

Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is responsible for high economic losses in swine herds across the globe. Pleuropneumonia is characterized by severe respiratory distress and high mortality. The knowledge about the interaction between bacterium and host within the porcine respiratory tract has improved significantly in recent years. A. pleuropneumoniae expresses multiple virulence factors, which are required for colonization, immune clearance, and tissue damage. Although vaccines are used to protect swine herds against A. pleuropneumoniae infection, they do not offer complete coverage, and often only protect against the serovar, or serovars, used to prepare the vaccine. This review will summarize the role of individual A. pleuropneumoniae virulence factors that are required during key stages of pathogenesis and disease progression, and highlight progress made toward developing effective and broadly protective vaccines against an organism of great importance to global agriculture and food production.