David John Hampson

Swine dysentery (SD) is a severe diarrhoeal disease of pigs caused by Serpulina hyodysenteriae. Certain components of large intestinal microflora facilitate colonisation by the spirochaete, but reduced fermentation in the large intestine protects pigs from SD. In this experiment, we treated wheat based diets by extrusion and/or addition of exogenous enzymes to reduce the amount of substrate reaching the large intestine, and monitored the microflora. Six pigs on each dietary were then infected with S. hyodysenteriae. Both the addition of enzyme and extrusion caused a small but significant reduction in total numbers of anaerobes. No consistent changes were observed in the distribution of specific bacterial species and pigs in all treatments groups developed SD. Neither extrusion, enzyme addition, nor the combination of both reduced fermentation sufficiently to inhibit colonisation by S. hyodysenteriae.

Postweaning colibacillosis in piglets is associated with proliferation and colonisation of β-haemolytic entertoxigenic Escherichia coli in the small intestine. The pathogenesis of this disease is complex, with dietary composition being an important contributing factor. In this experiment the interaction between dietary fibre and intestinal β-haemolytic E. coli populations was studied in 33 experimentally infected newly-weaned piglets. A source of soluble fibre (guar gum) was added to the base diet (cooked rice/ animal protein) to increase the dietary soluble fibre content from 1 to 6% on a dry matter basis. The base diet and the guar gum diet were fed to a separate group of piglets for a week from weaning. Experimental inoculation with haemolytic E. coli took place 48 hours after weaning, and all intestinal samples were taken 6-7 days postweaning. Pigs fed the guar gum diet had significantly higher (p<0.05) number of colony-forming units (CFU) of β-haemolytic E. coli per gram of mucosal scraping at 50% along the length of the small intestine (8.0 x 10 9 compared to 1.3 x 10 4 CFU/gram mucosal scraping). No significant differences in haemolytic E. coli numbers were found in the large intestine between diets. Addition of guar gum to the base diet also resulted in reduced weight gain after weaning (p<0.0001). Soluble fibre in the diet appears to be detrimental to growth and health of pigs in the first week postweaning.

Serpulina pilosicoli is recognised as the causative agent of intestinal spirochaetosis (IS), a diarrhoeal disease which affects a variety of vertebrate hosts including pigs, dogs, birds and humans, It is commonly isolated from the faeces of individuals in developing communities, HIV positive patients and homosexual males in western societies. Additionally S. pilosicoli has been isolated from the bloodstream of debilitated patients. In order to determine the potential sources of human contamination, water from a lake at Perth Zoological Gardens and faeces from 43 water birds frequenting the lake were examined. S. pilosicoli was isolated and identified from eight of the 43 faecal samples (18.6%) and from three of the seven (42.8%) samples of lake water. A subset of 17 faecal samples were subjected to DNA extraction and PCR after primary culture, and eight (47%) were positive for S. pilosicoli DNA. Experimentally, S. pilosicoli was shown to survive in lake water for more than one month and in tap water for from one to 14 days. A volunteer who drank 1 x 10 9 cells of an S. pilosicoli strain mixed with tap water on three successive days became colonised with the same strain. The results suggest that water contaminated with faeces containing S. pilosicoli could be a source of infection for humans and animals.

Serpulina hyodysenteriae and Serpulina pilosicoli are the respective antiological agents of swine dysentery and intestinal spirochaetosis. Both species have been shown to be genetically diverse but the mechanisms accounting for the variation have not been investigated. Originally, most bacterial species were thought to be clonal and although recombination occurred it was presumed to be too infrequent to disrupt linkage disequilibrium. The recent application of the index of association (Ia) to MEE data sets has shown that bacteria may occupy a spectrum of population structures. Whilst the majority of species are clonal, some naturally transformable species have been shown to be panmicitc (ie high levels of recombination have disrupted linkage disequilibrium) whilst others have an intermediate population structure. The Ia was applied to 231 S. hyodysenteriae isolates that were divided into 50 electrophoretic types (ETs), and the population structure was found to be epidemic (ie significant levels of background recombination occurring with a large number of isolates restricted to certain ETs that may have survival or virulence advantages). In contrast 145 S. pilosicoli isolates obtained from humans in the Highlands of PNG divided in 27 ETs had a completely panmictic population structure. The results may reflects the different epidemiological aspects of each disease. The potential mechanisms for recombination in each species require further investigation.