No abstract

Lactobacillus plantarum is a frequently encountered inhabitant of the human intestinal tract, and some strains are marketed as probiotics. Their ability to adhere to mannose residues is a potentially interesting characteristic with regard to proposed probiotic features such as colonization of the intestinal surface and competitive exclusion of pathogens. In this study, the variable capacity of 14 L. plantarum strains to agglutinate Saccharomyces cerevisiae in a mannose-specific manner was determined and subsequently correlated with an L. plantarum WCFS1-based genome-wide genotype database. This led to the identification of four candidate mannose adhesin-encoding genes. Two genes primarily predicted to code for sortase-dependent cell surface proteins displayed a complete gene-trait match. Their involvement in mannose adhesion was corroborated by the finding that a sortase (srtA) mutant of L. plantarum WCFS1 lost the capacity to agglutinate S. cerevisiae. The postulated role of these two candidate genes was investigated by gene-specific deletion and overexpression in L. plantarum WCFS1. Subsequent evaluation of the mannose adhesion capacity of the resulting mutant strains showed that inactivation of one candidate gene (lp_0373) did not affect mannose adhesion properties. In contrast, deletion of the other gene (lp_1229) resulted in a complete loss of yeast agglutination ability, while its overexpression quantitatively enhanced this phenotype. Therefore, this gene was designated to encode the mannose-specific adhesin (Msa; gene name, msa) of L. plantarum. Domain homology analysis of the predicted 1,000-residue Msa protein identified known carbohydrate-binding domains, further supporting its role as a mannose adhesin that is likely to be involved in the interaction of L. plantarum with its host in the intestinal tract.

The induction of transmission-blocking immunity as a potential tool in malaria control was first reported in 1976 by Gwadz (1) and Carter and Chen (2) for the avian malaria parasite Plasmodium gallinaceum. Subsequent reports confirmed that the immunogens were present on the surface of both male and female gametes (3, 4). Similar results were reported for a simian malaria parasite, P.knowlesi (5), and the murine P. yoelii (6). This work was extended to the midgut stages of P. gaUinaceum by Kaushal and coworkers (7-10). Since the introduction of the in vitro culture for P. falciparum (I 1), good progress has been made ill biochemistry and molecular biology of the asexual parasites. The sexual stages, however, demanded special culture conditions. The availability of gametocytes and gametes as well as the establishment of routine in vitro infection of mosquitoes (12) were basic for further studies on this human malarial parasite. In 1983 Rener et al. (13) demonstrated that monoclonal antibodies (mAb) 1 against P.falciparum gametes could interfere with the transmission of this parasite to mosquitoes.We here present results of experiments regarding the nature of antigens on the sexual stages of P. falciparum, and their involvement in the blocking of transmission by monoclonal and polyclonal antibodies. These antigens are sequentially expressed in gametocytes, on the surface of gametes, or on ookinetes.

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) of deer and elk, and little is known about its transmissibility to other species. An important factor controlling interspecies TSE susceptibility is prion protein (PrP) homology between the source and recipient species/genotypes. Furthermore, the ef®ciency with which the proteaseresistant PrP (PrP-res) of one species induces the in vitro conversion of the normal PrP (PrP-sen) of another species to the protease-resistant state correlates with the cross-species transmissibility of TSE agents. Here we show that the CWD-associated PrPres (PrP CWD ) of cervids readily induces the conversion of recombinant cervid PrP-sen molecules to the protease-resistant state in accordance with the known transmissibility of CWD between cervids. In contrast, PrP CWD -induced conversions of human and bovine PrP-sen were much less ef®cient, and conversion of ovine PrP-sen was intermediate. These results demonstrate a barrier at the molecular level that should limit the susceptibility of these non-cervid species to CWD. Keywords: cell-free conversion/chronic wasting disease (CWD)/prion protein (PrP)/scrapie/transmissible spongiform encephalopathy (TSE)

More than a million cattle infected with bovine spongiform encephalopathy (BSE) may have entered the human food chain. Fears that BSE might transmit to man were raised when atypical cases of Creutzfeldt-Jakob disease (CJD), a human transmissible spongiform encephalopathy (TSE), emerged in the UK. In BSE and other TSE diseases, the conversion of the protease-sensitive host prion protein (PrP-sen) to a protease-resistant isoform (PrP-res) is an important event in pathogenesis. Biological aspects of TSE diseases are reflected in the specificities of in vitro PrP conversion reactions. Here we show that there is a correlation between in vitro conversion efficiencies and known transmissibilities of BSE, sheep scrapie and CJD. On this basis, we used an in vitro system to gauge the potential transmissibility of scrapie and BSE to humans. We found limited conversion of human PrP-sen to PrP-res driven by PrP-res associated with both scrapie (PrP[Sc]) and BSE (PrP[BSE]). The efficiencies of these heterologous conversion reactions were similar but much lower than those of relevant homologous conversions. Thus the inherent ability of these infectious agents of BSE and scrapie to affect humans following equivalent exposure may be finite but similarly low.