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To elucidate the role of Streptococcus uberis adhesion molecule (SUAM) in the pathogenesis of S. uberis mastitis, sua deletion in S. uberis UT888 was achieved by homologous recombination using a thermosensitive plasmid. The deletion mutant was analyzed for sua deletion by PCR, southern blot and DNA sequencing, and was designated Δsua S. uberis UT888. As compared to the isogenic parent strain, Δsua S. uberis UT888 did not produce SUAM based on SDS-PAGE gel and western blot. Deletion of sua and lack of expression of SUAM by Δsua S. uberis UT888 markedly reduced the ability of the sua gene deletion mutant of S. uberis to adhere to and internalize into mammary epithelial cells. These results confirm the central role of SUAM in adherence to and internalization of S. uberis into host cells., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Streptococcus suis is an important swine pathogen and a zoonotic agent. Differences in virulence have been noted among the 33 described serotypes, serotype 2 being considered the most virulent. In this study, we aimed at assessing the serotype distribution and the production of virulence-associated markers by strains recovered from diseased pigs in the United States (U.S.). Results showed that among the 100 strains evaluated, serotype 3 (20% of the isolates) and serotype 2 (17%) were the most prevalent. We then investigated the presence in these isolates of the genes sly, epf and mrp, encoding the virulence-associated markers suilysin (SLY), extracellular factor (EF) and muramidase-released (MRP) protein, respectively. The effective production of the markers by the strains was also verified. Results showed that the presence of the gene did not always correlate with actual expression of the respective protein. In the case of MRP, this was due, in most cases, to frameshift mutations at the 5' end of the gene resulting in premature stop codons. The most prevalent phenotypes among U.S. strains were MRP(+)EF(-)SLY(-) (40%) and MRP(-)EF(-)SLY(+) (35%). Serotype distribution greatly differed from that reported in several European countries, as did the production of virulence markers, particularly for serotype 2. On the other hand, our results for the U.S. S. suis isolates are similar to those reported for Canadian strains, suggesting a common status in North America.

Streptococcus suis is an economically important, zoonotic pathogen causing death and disease in swine. The objectives of this study were to develop a signature-tagged mutagenesis (STM) system for S. suis serotype 2 and to identify genes required for in vivo virulence. Identification of such candidate genes may lead to a better understanding of the pathogenesis of S. suis and may provide substrate for the discovery of new vaccines. A novel STM approach was designed to allow for a higher throughput assay of mutants using the Luminex xMAP system. Additionally, to speed the identification process, a direct genomic DNA sequencing method was developed that overcomes the problems associated with the presence of repetitive insertion sequences. Approximately 2600 mutants were screened through both mouse and caesarian-derived, colostrum-deprived (CDCD) pig models. The disrupted ORF was identified for each potential attenuated mutant, and mutants with distinct and unique mutated ORFs were analyzed individually for attenuation in mouse and CDCD pig models. A variety of genes were identified, including previously known genes essential to the virulence of other organisms, genes involved in capsule biosynthesis, a regulator of suilysin expression, and several conserved or predicted genes. Of the 22 mutants identified as attenuated in either animal model, eight insertion mutants caused no mortality in both mouse and pig models.