PLATES XXVIII AND XXIX NEONATAL diarrhoea in piglets follows the proliferation of certain strains of Escherichia coli in the small intestine (Smith and Jones, 1963). These enteropathogenic strains synthesise enterotoxins which produce diarrhoea and dehydration that frequently result in the death of the piglets (Kohler, 1968;Smith and Gyles, 1970;Smith and Linggood, 1971). The rapid proliferation of E. coli in the small intestine appears to be attributable to the ability of the bacteria to attach themselves to the intestinal epithelium (Arbuckle, 1970; Drees and Wader, 1970a and b; Bertschinger, Moon and Whipp, 1972) and thereby avoid removal from the small intestine by peristalsis (Dixon, 1960). Sojka (1965) noted that the majority of E. coli strains isolated from cases of neonatal piglet diarrhoea possess a surface antigen designated K88, and it has been shown that this antigen is an essential virulence determinant (Smith and Linggood, 1971 ;Jones and Rutter, 1972) apparently because it enabled K88-positive E. coli to attach to the intestinal lining (Jones and Rutter, 1972).To investigate the interaction between the host mucosal surface and K88-positive E. coli a convenient test system is essential. The K88 antigen agglutinates guinea-pig red cells (Stirm et al., 1967;Jones and Rutter, 1974), and attempts to study the chemical aspects of adhesion by means of this reaction have been reported (Gibbons, Jones and Sellwood, 1975). It would have been preferable to use a natural intestinal receptor, but the technique involving adhesion of E. coli to disks of intestinal tissue (Jones and Rutter, 1972) is laborious. This paper describes a simple in-vitro technique that demonstrates adhesion of K88-positive E. coli to brush borders from pig intestinal cells; a survey of pigs in respect of the ability of their brush borders to adhere to E. coli is also described. MATERIALS AND METHODS

Evidence is presented that a dominant allele, S, is expressed as a receptor for K88 on the brushborder surface of the pig intestinal cell. The homozygous recessive (ss) lacks this receptor. The receptor enables K88 - positive coliforms to adhere to the gut of the piglet which they must do if they are to cause neonatal diarrhoea. The homozygous recessive is thus a disease resistant animal.A possible reason for the persistence of the dominant (susceptible) gene is given.

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S U M M A R YThe K99 antigen common to some bovine strains of Escherichia coli caused mannose-resistant haemagglutination of sheep erythrocytes and was shown to be responsible for the attachment of Kgg-positive bacteria to calf brush-border preparations because (i) strains grown at 18 "C did not produce K99 antigen, cause haemagglutination, or attach to brush borders; (ii) a K12 (K99+) recombinant strain showed both haemagglutinating activity and attachment to brush borders whereas, before it received the K99 plasmid, therecipient strain was negative in both respects; and (iii) cell-freeextracts of K99 antigen showed haemagglutinating activity and inhibited the attachment of Kgg-positive organisms to brush borders.K99 antigen appears to be a virulence determinant in the pathogenesis of neonatal calf diarrhoea. It is readily demonstrated by haemagglutination and brushborder attachment tests.

Four cistrons (adh) involved in the expression of the K88 adhesion system have been identified and mapped. Three of these (adh A, adh B and adh C) are located in a single operon (I) whereas the fourth (adh D) is expressed from a separate promoter (operon II). The polypeptides encoded by these cistrons have been identified and their role in the formation and regulation of K88 fimbriae (pili) is discussed.

Purified axial filaments from eight serotypes of Treponema hyodysenteriae and two nonpathogenic intestinal spirochaetes were characterized by SDS-PAGE and Western blotting. Axial filaments of all ten strains had similar SDS-PAGE profiles; five major axial filament polypeptides were identified, with molecular masses of 43.8, 38, 34.8, 32.8 and 29.4 kDa. Hyperimmune gnotobiotic pig serum raised against purified axial filaments of strain P 18A (serotype 4) cross-reacted with all other serotypes and with the non-pathogens, and convalescent serum taken from a pig with persistent swine dysentery also showed a strong response to the axial filament polypeptides. Hyperimmune gnotobiotic pig serum raised against axial filaments failed to agglutinate viable organisms and did not inhibit growth in vitro. Hence, the axial filaments of T. hyodysenteriae have been identified as major immunodominant antigens, although the role that antibodies to these antigens play in protection has yet to be established.

Outer envelopes of Treponema hyodysenteriae strains PI 8A and VS1 were prepared and characterized by SDS-PAGE. In Western blot analysis of eleven strains of T. hyodysenteriae and two intestinal non-pathogenic spirochaetes, polyclonal antiserum raised to the outer envelopes of strain P18A contained antibodies primarily to two polypeptides. A 45 kDa polypeptide was present in only two strains of T. hyodysenteriae, P 18A and MC52/80, whereas another antigen of 16 kDa was common to all eleven strains of T. hyodysenteriae but was not present in the two nonpathogens. Immunogold labelling of whole organisms suggested that the 16 kDa antigen was present on the surface of the spirochaetes. In in vitro tests the serum agglutinated and inhibited growth of only the T. hyodysenteriae strains, suggesting that antibodies to the 16 kDa antigen were responsible for these activities. Serum from a gnotobiotic pig infected with T. hyodysenteriae strain P18A had antibodies to the 16 kDa antigen alone and also possessed agglutinating and growth-inhibitory activities.

S U M M A R YThe K88 antigen of Escherichia coli specifically adheres to the piglet intestinal cell; a solution of this antigen agglutinates guinea-pig red cells at 4 "C. The latter reaction was used as a model of the former, using inhibition of haemagglutination as an index of specific combination with the K88 adhesin. Inhibition was found with mucous glycoproteins and chemical modification of their heterosaccharide residues by mild acid hydrolysis, periodate oxidation or the Smith degradation procedure suggested that the terminal P-D-galactosyl structure in a heterosaccharide sidechain of a glycoprotein might combine specifically with the K88 adhesin and inhibit haemagglutination. One serum glycoprotein (fetuin), after exposure of its subterminal P-D-galactosyl residue, also inhibited haemagglutination, but high inhibitory activity was exhibited by some submaxillary glycoproteins in which this structure was absent or not prominent. It was concluded that in some cases inhibition of haemagglutination by glycoprotein was non-specific. No inhibition was found using glycosaminoglycans, glycogen or any simple sugar or glycoside. Sow colostrum was inhibitory but this was associated mainly with its y-globulin fraction. Some inhibitory activity was traced to a colostral glycopeptide fraction of low molecular weight but the smaller colostral oligosaccharides were not inhibitory; the composition of these components in sow colostrum is reported.