Research in Veterinary Bacteriology
Poultry
Mycoplasma gallisepticum
Tools for genetic manipulation. We have developed the first plasmid that can replicate independently in this species and are using it to gain a better understanding of the control of gene expression and of protein transport in this pathogen.
Molecular basis for virulence. We are also exploring the molecular basis of virulence in M. gallisepticum by generating knockout mutants and assessing their virulence in infected chickens. This has enabled the mapping of a number of novel virulence genes.
Expression of foreign genes. A parallel project is examining the capacity of foreign genes expressed in a vaccine strain of M. gallisepticum to induce protective immune responses in vaccinated chickens.
Molecular basis for antigenic variation. We are further elucidating the molecular basis for control of transcription from members of the large gene family encoding the variably expressed major cell surface protein of M. gallisepticum.
Colibacillosis
Only specific strains of E. coli can cause respiratory disease in chickens. These strains carry virulence plasmids. We are genetically mapping one of these plasmids to establish which of the genes it carries are responsible for pathogenicity.
Pigs
Mycoplasma hyopneumoniae
Lipoproteins are key factors in the interaction between mycoplasmas and their hosts. We are systematically characterising the lipoproteins of M. hyopneumoniae by mutagenising their genes to enable their expression in and purification from E. coli, then using functional biochemical assays to examine their role in infection.
Dogs
Pyometra
We have established that E. coli associated with pyometra commonly possess virulence genes that are also found in strains that cause urinary tract disease. Using an experimental model of pyometra we are now examining whether adhesion to the endometrium is a crucial step in the pathogenesis of this disease.
Horses
Rhodococcus equi
We have developed techniques to allow rapid differentiation of virulent and avirulent R. equi in measured air samples. These techniques have been used to identify the areas on horse studs that pose the highest risk to young foals, and also to examine the potential for this pathogen to be transmitted directly from foal to foal. Our recent findings suggest that transmission between foals may be more significant as a source of disease than dust from the environment.
Transport-associated pneumonia
Using adaptations of the methods we developed to study rhodococcal pneumonia, we are investigating the bacterial pathogens associated with pneumonia after long-distance transport, both by road and air.
Cattle
Streptococcal mastitis
While current approaches to mastitis management have resulted in effective control of most of the common causes of mastitis in Australian herds, Streptococcus uberis remains a refractory problem in some herds. Using molecular epidemiological methods we examined the epidemiology of S. uberis mastitis and found that in some herds it appears to be spreading from udder to udder. We are using PCR to determine the prevalence of S. agalactiae infection in the national dairy herd.
