The major surface Vsp proteins of Brachyspira hyodysenteriae form antigenic protein complexes.

The Vsp proteins are the major outer membrane proteins of Brachyspira hyodysenteriae, the causative agent of swine dysentery. Eight vsp genes have been identified in B. hyodysenteriae strain B204, arranged into two four-gene loci, and at least two of the corresponding proteins are produced in vitro. The aims of this study were to characterise the vsp genes of the virulent Australian B. hyodysenteriae strain X576 and their corresponding proteins, Genomic sequence comparison with strains B204 and WA1 demonstrated that the number of vsp genes varies between B. hyodysenteriae strains, although the chromosomal locations of the vsp gene loci are consistent. We identified two additional vsp-like genes, designated vspI and vspJ, in each of the three strains. Double SDS-PAGE was used to demonstrate that Vsp proteins of B. hyodysenteriae strain X576 form multimeric protein complexes in the outer membrane that are stable in 6M urea but dissociate after boiling. The Vsp complexes primarily consisted of VspF but also contain VspE and VspI. VspD was also found in a series of complexes slightly larger than the more abundant VspF complexes. Vsp proteins are purported to be antigenic; however little direct data are available to support this claim. In this study convalescent pig sera did not bind denatured Vsp proteins by Western blotting, but did bind the Vsp complexes on Western blots, showing that conformational epitopes may be important in immune recognition of these major outer membrane proteins. This is the first definitive demonstration of the antigenicity of these proteins in swine dysentery.

Pathotypes and serogroups of enterotoxigenic Escherichia coli isolated from pre-weaning pigs in north Vietnam.

The contribution of enterotoxigenic Escherichia coli (ETEC) to pre-weaning diarrhoea was investigated over a 6 month period at five selected commercial piggeries (CPs) in north Vietnam with at least 100 sows each. Diarrhoea was found to affect 71.5% of the litters born during the period of study. Of 406 faecal specimens submitted for bacteriological culture, 200 (49.3%) yielded a heavy pure culture of E. coli and 126 (31%) were confirmed by PCR to carry at least one of eight porcine ETEC virulence genes. ETEC was responsible for 43% of cases of diarrhoea in neonatal pigs during the first 4 days of life and 23.9% of the remaining cases up until the age of weaning. Pathotypes were determined by PCR for the 126 ETEC isolates together with 44 ETEC isolates obtained from village pigs (VPs) raised by smallholder farmers. The CP isolates belonged to five pathotypes, four of which were also identified in VP isolates. Haemolytic serogroup O149 : K91 isolates that belonged to F4/STa/STb/LT were most commonly identified in both CPs (33% of isolates) and VPs (45.5%). Other combinations identified in both production systems included O64 (F5/STa), O101 (F4/STa/STb) and O-nontypable (F-/STb). A high proportion of CP isolates (22.3%) possessed all three enterotoxins (STa/STb/LT), lacked the genes for all five tested fimbriae (F4, F5, F6, F41 and F18) and belonged to serogroup O8. These unusual O8 F- isolates were haemolytic and were isolated from all ages of diarrhoeic piglets at each CP, suggesting that they have pathogenic potential.