School of Pathology and Laboratory Medicine

Bacterial Pathogenesis

Collaborators

Dr John Davies (Monash University)
Assoc/Prof Kathy Heel (UWA)
Dr Begona Heras (LaTrobe University)
Assoc/Prof Charlene Kahler (UWA)
Prof Russell Carlson (Complex Carbohydrate Research Centre, Athens, USA)
Dr Azadi Parastoo (Complex Carbohydrate Research Center, Athens, USA)
Mr Shakeel Mowlaboccus (PhD candidate)
Assoc/Prof Christopher Peacock (UWA)
Dr Paul Rigby (UWA)
Dr Martin Scanlon (Monash University)
Dr David Stephens (Emory University, UWA)
Dr Keith Stubbs (UWA)
Dr Yih-ling Tzeng (Emory University, USA)
Dr Alice Vrielink (UWA)

 

Dr Charlene Kahler's work has involved the molecular analysis of the pathogenesis of Neisseria meningitidis and Neisseria gonorrhoeaeN. meningitidis and N. gonorrhoeae are two closely related obligate human pathogens.

Projects on N. meningitidis 

Background

N. meningitidis is the causative agent of epidemic meningococcal meningitis and septic shock. It colonises mucosal surfaces of the nasopharynx and in susceptible individuals, particularly children under the age of two years, the bacterium becomes systemic resulting in fatal bacteremia. Despite the continued sensitivity of the meningococcus to multiple widely available antibiotics, including penicillin, the case-fatality ratio for meningococcal disease remains around 10%–14%. Vaccines have been developed based on the polysaccharide capsules to prevent community spread and therefore have become an effective means of reducing meningococcal disease. With the recent release of the serogroup B subunit vaccine there is considerable interest in understanding the antigenic diversity of this pathogen and how this may change when the vaccine is introduced into the community.

Pathogenesis of N. meningitidis 

The ecology of N. meningitidis is very complex with some strains very rarely, if ever, causing disease, while other strains are more associated with disease. Meningococcal pathogenesis has been predicated upon the ability to phase vary and regulate virulence factors such as capsule, lipooligosaccharide and pilin for effective invasion into host cells. We are currently comparing the ability of different isolates to regulate their virulence determinants and how this affects their ability to cause disease.

 The Endotoxin Biosynthesis Pathway in Neisseria DrCharleneKahler1

Endotoxin is synthesised by a series of enzymes on the cytoplasmic face of the inner membrane. It is then transported across the inner membrane to the outer membrane by an ABC transporter complex. To find out more please refer to Piek and Kahler (Front Cell Infect Microbiol. 2012 Dec 20;2:162). 

NeuNAc= sialic acid; Hep= heptose; Kdo= keto-octulosonic acid; GlcNAc= N-acety-glucosamine; Glc= UDP-glucose; Gal= UDP-galactose; PEA=phosphoethanolamine.

Epidemiology of N. meningitidis

The new serogroup B vaccine contains four major antigens which elicit a cross-protective antibody response. Previous studies have indicated that around 75% of strains may be covered by the vaccine. Since no studies have been done as yet on Western Australia, we are sequencing the entire meningococcal collection from 2000 and will examine this collection for the possession of the antigens necessary for vaccine efficacy.

DrCharleneKahler2

eBurst of meningococcal clonal complexes.



Projects on N. gonorrhoeae

Background 

Neisseria gonorrhoeae on the other hand, is the causative agent of the sexually transmitted disease (STD) gonorrhoea. Comparatively, the rate of disease in developing nations is approximately ten times that of developed countries and globally approximately 20-60 million new cases are reported per annum (WHO). In males, gonococcal infection is generally acute and resolves rapidly with treatment. However, higher morbidity is seen in women as the infection remains asymptomatic and without treatment progresses to pelvic inflammatory disease (PID) resulting in infertility in approximately one third of patients. Unlike meningococci, this organism is increasingly resistant to antibiotics with a recent report of the emergence of a “superbug” resistant to all antibiotics. To date no successful vaccine strategies have been developed for this organism, primarily because the cell surface proteins expressed by this organism are highly antigenically variable, and elicit limited immunological protection against other strains. As a result individuals can contract the disease multiple times throughout their lifetime.

Biogenesis in Gram negative envelope and the search for novel drug targets. 

The Gram negative envelope consists of the cytoplasmic membrane, outer membrane and the intervening compartment, the periplasm, containing the peptidoglycan cell wall. The Gram-negative envelop is a rich area for the future development of drugable targets as (a) many of the components are essential for cellular life, (b) accessible to drugs in the environment via diffusion past the outer membrane and (c) provides potential synergies with current antibiotics which target processes in the periplasm. 

We are currently pursuing targets in the endotoxin biosynthesis pathway and in the protein oxidation and isomerization pathways. In these projects we have solved the crystal structures of the protein and are using rational drug design to find candidate inhibitors of these enzymes.


CharleneKahlerFigure3 

The structure of neisserial oxidoreductase showing the binding cleft

Refer to Vivian et al, J Biol Chem. 21;283(47):32452-61 for more information.