Streptococcus gordonii strains resistant to fluorodeoxyuridine contain mutations in the thymidine kinase gene and are deficient in thymidine kinase activity

Clinical and microbiological responses of volunteers to combined intranasal and oral inoculation with a Streptococcus gordonii carrier strain intended for future use as a group A streptococcus vaccine

Streptococcus gordonii shows promise as a live mucosal vaccine vector for immunization against respiratory pathogens. In preparation for clinical trials to evaluate S. gordonii engineered to express group A streptococcal M protein antigens, we characterized the responses of 150 healthy volunteers to combined nasal and oral inoculation with approximately 1.5 x 10(9) CFU of SP204(1-1), an S. gordonii strain not bearing vaccine antigens. SP204(1-1) was selected for resistance to streptomycin and 5-fluoro-2-deoxyuridine to distinguish it from indigenous flora. In two antibiotic treatment studies, we performed serial culturing of nose, mouth, and saliva samples from 120 subjects treated with azithromycin beginning 5 days after inoculation to determine whether SP204(1-1) could be rapidly eliminated should safety concerns arise. A natural history study was performed to assess the time until spontaneous eradication in the remaining 30 subjects, who did not receive the antibiotic and who were monitored with repeated culturing for 14 weeks after inoculation. SP204(1-1) was generally well tolerated. Symptoms reported most often within 5 days of inoculation were nasal congestion (36%), headache (30%), and sore throat (19%). The strain was detected by culturing in 98% of subjects. A single dose of azithromycin eliminated colonization in 95% of subjects; all subjects receiving a 5-day course of an antibiotic showed clearance by day 11. Without the antibiotic, 82% of subjects showed spontaneous eradication of the implanted strain within 7 days, and all showed clearance by 35 days. The results of these clinical trials provide encouragement that the use of S. gordonii as a live mucosal vaccine vector is a feasible strategy.

Biological consequences of antigen and cytokine co-expression by recombinant Streptococcus gordonii vaccine vectors

To test the effect of co-expression of immunomodulatory molecules, together with target antigen, two recombinant Streptococcus gordonii strains were constructed which secreted either murine interleukin-2 (IL-2) or interferon-gamma (IFN-gamma) in addition to a surface anchored test antigen (the conserved C-repeat region (CRR) of the M6 protein of Streptococcus pyogenes). The secretion of functional cytokines by S. gordonii was achieved by in-frame fusion of sequences encoding mature IL-2 or IFN-gamma to the sequences encoding the leader signal of the M6 protein. Expression of the M protein CRR region from a separate chromosomal site produced double recombinants expressing a secreted cytokine and the M protein CRR region anchored to the surface. Protein expression was verified by streak blot, immunoblot, and ELISA on both the single and double recombinants. A cytokine bioassay using HT-2 cells verified biological activity of recombinant IL-2 secreted from S. gordonii. When mice were immunized subcutaneously with the different S. gordonii expression strains, cytokine co-expression apparently modulated the systemic immune response. These results show that streptococci can deliver biologically active molecules such as cytokines along with antigens to the immune system. These results demonstrate that a cytokine-secreting, noninvasive, bacterial vaccine vector can be used to modulate immune responses to a co-expressed antigen.

Conserved DegP protease in gram-positive bacteria is essential for thermal and oxidative tolerance and full virulence in Streptococcus pyogenes

The DegP protease, a multifunctional chaperone and protease, has been shown to be essential for virulence in gram-negative pathogens such as Salmonella enterica serovar Typhimurium, Brucella abortus, Yersinia enterocolitica, and Pseudomonas aeruginosa. The function of DegP in pathogenesis appears to be the degradation of damaged proteins that accumulate as a result of the initial host response to infection, which includes the release of reactive oxygen intermediates. Additionally, the DegP protease plays a major role in monitoring and maintaining the Escherichia coli periplasm and influences E. coli pilus biogenesis. We report here the identification of highly homologous enzymes in Streptococcus pyogenes, Streptococcus gordonii, Streptococcus mutans, Staphylococcus aureus, and Enterococcus faecalis. Moreover, the phenotype of an insertionally inactivated degP allele in S. pyogenes is similar to that reported for E. coli, with temperature sensitivity for growth and enhanced sensitivity to reactive oxygen intermediates. Virulence studies in a mouse model of streptococcal infection indicate that a functional DegP protease is required for full virulence. These results suggest DegP as an attractive broad-spectrum target for future anti-infective drug development.