F1-fimbrial lectins from Escherichia coli and its relation with the spermagglutination phenomena in boar semen.

Background: E. coli is a well known commensal of the big bowel of birds and mammals, but some strains are able to colonise other niches as well and are the causative agent of several diseases in man and his lifestock. When present in semen, E. coli can cause spermagglutination and affect reproduction.
Aims: This study aims at identifying the surface components involved in spermagglutination in boar semen and to investigate the effect of contamination of semen on litter size.
Methods: E. coli were isolated from the semen of boars in Cuban pig farms. The isolates were characterised using electron microscopy, agglutination of erythrocytes and yeast and PCR to identify important fimbrial genes. Sows were artificially inseminated.
Results: Hundred fifteen boar semen samples were collected from two different farms. E. coli was found to be the main contaminant, being present in 79% of the samples. Other contaminating bacteria belonged to the genera Proteus, Serratia, Aerobacter, Klebsiella, Staphylococcus, Streptococcus and Pseudomonas. Eight isolates in vitro agglutinate boar sperm cells, baker's yeast and rabbit erythrocytes that is inhibited by methyl-alpha,D-mannopyranoside. All isolates except one express appendages that highly resemble F1 (Type 1) fimbriae. Six E. coli isolates express F1 or F1-like fimbriae, one isolate shows strong agglutinating properties and expresses fimbriae that morphologically look similar to F1 fimbriae but does not amplify the fimH gene by PCR, and one isolate is not expressing fimbrial structures but amplifies fimH. The latter probably presents the adhesive subunit on its surface as a non-fimbrial adhesin. The eight E. coli strains were analyzed for the presence of the F1 operon (fimA, fimC, fimD, fimG and fimH) and sequences were analyzed. All FimH sequences obtained are identical except for one strain, where two mutations were found, one in the lectin and one in the pilin domain. In view of the apparent differences in agglutination properties of the different strains, it is suggested that subunits underlying the adhesins are responsible for conformational differences in the sugar-binding site of FimH. A good candidate is FimG, in which a large number of important substitutions were observed. Knock out of fimH (by Lambda Red mediated homologous recombination) was used to show that F1 fimbriae mediate boar sperm agglutination. The transformants obtained completely lost their sperm agglutination properties. We conclude that, for the strain tested, the sperm agglutination is mediated by the lectin domain of FimH.
The analysis of the offspring showed that the litter size was significantly reduced (PConclusion: The results presented in this study demonstrate that, in order to improve pig production, quality control of the semen is of paramount importance and that semen contaminated with E. coli should not be used for artificial insemination.