Streptococcus suis and Staphylococcus aureus are both porcine and zoonotic pathogens. The molecular biology of these organisms is well defined internationally, but less so with respect to Australian pigs. This thesis characterised the molecular biology of S. suis serotype 2 and methicillin-resistant S. aureus (MRSA) from Australian pigs, and tested the hypothesis that, based on molecular traits, Australian strains would be indistinguishable from those observed overseas.
Four studies were carried out. The first considered the molecular ecology of S. suis causing infections in pigs in Australia. The second compared human clinical isolates with those recovered from diseased and healthy pigs. This second study also considered the validity of different biological materials for detecting S. suis type 2 in pigs by bacteriological culture. These first two studies used virulence-associated genotyping, random amplified polymorphic DNA PCR and pulsed-field gel electrophoresis. A third study then employed multilocus sequence typing. This enabled the unambiguous comparison of Australian S. suis type 2 with well characterised strains from abroad, thus informing on the virulence-potential of S. suis type 2 in Australian pigs. The fourth and final study assessed the utility of a sampling and detection strategy designed to isolate MRSA from porcine nasal samples. A suite of molecular assays, including multilocus sequence typing, staphylococcal protein A gene typing, staphylococcal cassette chromosome mec typing and binary typing, helped to place Australian MRSA isolates into context with strains from abroad.
Findings indicate that global archetypes of virulent S. suis type 2 and livestock-associated MRSA (LA-MRSA) are harboured in the Australian pig herd. The economic and public health risks attributable to these organisms dictate that epidemiological studies will be needed in the future. Findings from this thesis will enable this to be done efficiently, both in Australia and abroad. This thesis has culminated in a new understanding, providing a basis for the implementation of specialised, yet pragmatic strategies, that are needed to efficiently sample for, detect and characterise S. suis type 2 and LA-MRSA present in the Australian pig herd.