Shigella Flexneri O Antigen Polysaccharides: Biosynthesis, Function In Virulence, And Interaction With IcsA/VirG
Funder
National Health and Medical Research Council
Funding Amount
$468,055.00
Summary
Shigella flexneri bacteria cause dysentery in millions of humans each year. The bacterium invades and replicates within the cells of the large intestine. Inside cells, S. flexneri is able to use the host cell's actin-based motility machinery to become motile within the cells, and this can be seen as F-actin comet tails extending from one end of the cell. Bacterial cell surface components residing in the outer membrane are important for the bacterium's ability to cause disease. Two of these compo ....Shigella flexneri bacteria cause dysentery in millions of humans each year. The bacterium invades and replicates within the cells of the large intestine. Inside cells, S. flexneri is able to use the host cell's actin-based motility machinery to become motile within the cells, and this can be seen as F-actin comet tails extending from one end of the cell. Bacterial cell surface components residing in the outer membrane are important for the bacterium's ability to cause disease. Two of these components (lipopolysaccharides (LPS) and their polysaccharide chains (O antigens), and IcsA-VirG protein)) are required for initiating actin polymerisation, and mutations affecting synthesis of these components reduce ability to cause disease. In previous studies we have found that O antigen and the synthesis and function of IcsA are interrelated. This project will study how the O antigens are synthesised and their chain length determined by the Wzz protein, and the Wzz structure in relation to its function will also be characterised. The role played by O antigen in intracellular motility will be studied to determine the mechanisms involved. Infection of cells and cell free extracts, antibodies, and an enzyme which specifically degrades the O antigen, will be used to study how O antigen affect the interaction between bacteria with human cell proteins. The relationship between O antigen and IcsA function will be studied using monoclonal antibodies raised to IcsA. The effect of LPS on the outer membrane protease IcsP will be investigated, as will the effect of LPS lipid A mutations on O antigen and virulence. These studies will contribute to a better understanding of the biosynthesis of an ubiquitous bacterial cell surface component (O antigen), its function as a virulence factor in bacterial interactions with host cells. This may lead to novel therapeutic strategies to prevent and control Shigellosis and other bacterial infections.Read moreRead less
Origins And Relationships Of Shigella And Enteroinvasive Escherichia Coli
Funder
National Health and Medical Research Council
Funding Amount
$377,310.00
Summary
Shigella is a well known highly infectious human pathogen with as few as 10 cells allowing effective spread by infected food or water, and also by person to person contact. Shigellosis is a particularly significant disease for children due to lack of pre-existing immunity and greater chance of transfer by fecal-oral route. One group of E. coli called Enteroinvasive E. coli (EIEC) resembles Shigella in many aspects from disease symptoms to biochemical properties. EIEC is a major cause of diarrhoe ....Shigella is a well known highly infectious human pathogen with as few as 10 cells allowing effective spread by infected food or water, and also by person to person contact. Shigellosis is a particularly significant disease for children due to lack of pre-existing immunity and greater chance of transfer by fecal-oral route. One group of E. coli called Enteroinvasive E. coli (EIEC) resembles Shigella in many aspects from disease symptoms to biochemical properties. EIEC is a major cause of diarrhoea in less developed countries and has also caused large outbreaks in developed countries. It is now clear that Shigella and E. coli are really one species. EIEC and Shigella strains are variants of E. coli with humans as the only host. However separation of the two in all records and most studies means that there is no integrated understanding of the forms. We aim to study the relationships of Shigella and EIEC and expect significant insights into the origins of Shigella-EIEC. This will facilitate diagnosis and understanding of the disease(s) and lead to a far better classification . EIEC-Shigella strains have arisen from other E. coli independently. This has happened seven times in the derivation of Shigella and we expect more such events with EIEC. An interesting phenomenon during this process is that strains tend to lose metabolic functions. In this study we will look at what, why and how functions are lost. O antigens are important in evading the host immune system. Shigella strains obtained many O antigens, the majority apparently from other species. This is quite likely the key to its success. We will look at how Shigella obtained new O antigens. This project will be significant in the understanding of Shigell-EIEC, a very significant human pathogen, and in general for understanding emergence of new pathogens.Read moreRead less
Dissemination And Virulence Properties Of The She Pathogenicity Island Of Shigella Flexneri.
Funder
National Health and Medical Research Council
Funding Amount
$110,625.00
Summary
Bacterial species belonging to the genus Shigella are responsible for intestinal diseases ranging from mild diarrhoea to life threatening bacillary dysentery. Such diseases kill over a million people, mainly infants in developing countries, every year and lead to serious morbidity and mortality even in industrialised countries with well developed health care systems. In many cases the virulence of Shigella species is augmented by large fragments of DNA, called pathogenicity islands, that carry g ....Bacterial species belonging to the genus Shigella are responsible for intestinal diseases ranging from mild diarrhoea to life threatening bacillary dysentery. Such diseases kill over a million people, mainly infants in developing countries, every year and lead to serious morbidity and mortality even in industrialised countries with well developed health care systems. In many cases the virulence of Shigella species is augmented by large fragments of DNA, called pathogenicity islands, that carry genes which contribute to the development of disease (pathogenesis) in humans. Pathogenicity islands are important genetic elements which appear to spread independantly throughout bacterial populations and therefore contribute to the emergence of new virulence traits in bacteria. Recently, we identified two related pathogenicity islands carried by both Shigella flexneri and other species of the genus Shigella. The two pathogenicity islands belong to a unique class of genetic elements found in Shigella species and virulent strains of the intestinal bacterium E. coli. Our current study is aimed at (1) understanding the mechanisms by which one of these islands, the she pathogenicity island, spreads from one bacterial strain to another to introduce disease-producing or virulence genes to new bacteria and (2) to study how the sigA virulence gene, carried on the she pathogenicity island, contributes to disease development in humans. We know that sigA encodes a protein toxin which contributes to the loss of fluid from the intestines of rabbits that have been experimentally infected with Shigella flexneri. We propose to study the structure and function of the SigA protein to determine how it interacts with tissues to produce a pathological state. Such studies will enhance our understanding of the process of disease development and contribute to the investigation and assessment of new strategies for therapeutic intervention.Read moreRead less
The Roles Of Lipoprotein Multigene Families In Pathogenesis Of Mycoplasma Pneumoniae
Funder
National Health and Medical Research Council
Funding Amount
$257,036.00
Summary
Mycoplasma pneumoniae is one of the most common causes of community acquired pneumonia. Although it can usually be successfully treated with antibiotics, it can result in more severe diseases and can be difficult to diagnose accurately. It has been identified as a target for vaccine development, but this has been hampered by the limited understanding we have of how it causes disease. The attempts at vaccination that have been made have resulted in vaccines which induced more severe, rather than ....Mycoplasma pneumoniae is one of the most common causes of community acquired pneumonia. Although it can usually be successfully treated with antibiotics, it can result in more severe diseases and can be difficult to diagnose accurately. It has been identified as a target for vaccine development, but this has been hampered by the limited understanding we have of how it causes disease. The attempts at vaccination that have been made have resulted in vaccines which induced more severe, rather than less severe, disease. Investigations of several other related bacteria have shown that they are able to vary their surface proteins and thus may evade the immune system, permitting them to cause more prolonged disease. Better understanding how this occurs, and what this enables the bacteria to do, may assist in developing improved vaccine strategies. This project aims to investigate the six gene families in Mycoplasma pneumoniae which are known to encode surface proteins and establish how and why the bacteria switch from one gene to another during infection. In addition the capacity of bacteria expressing different versions of the six surface proteins to adhere to different tissues will be investigated. Once this is known, these mechanisms may be able to be specifically disrupted to prevent a strain of Mycoplasma pneumoniae from being able to establish prolonged infections. Such a strain might be a useful basis for an effective vaccine.Read moreRead less