Lab Home
Welcome to the home page of the Laboratory of Bacterial Pathogenesis and Immunology at The Rockefeller University.
Vaccine and Antibiotics:
Our lab focuses both on the mechanisms by which gram-positive bacteria, particularly streptococci and staphylococci, cause disease and the development of methods to induce a protective mucosal immune response. One of the systems we use is the M protein from group A streptococci. M protein is the major virulence factor of this organism by virtue of its ability to impede attack by human phagocytes. Physicochemical and sequence analysis revealed that M protein is an alpha-helical coiled-coil rope-like structure extending nearly 60 nm from the cell surface. DNA sequence analysis of the COOH-terminal end of the M protein gene (the region involved in its attachment to the cell) revealed that it is highly homologous to comparable regions of nearly all known surface proteins from gram-positive bacteria. This indicates that the mechanism of anchoring surface proteins in these bacteria also may be conserved.
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Because gram-positive bacteria use their surface molecules to colonize or invade tissues, a knowledge of the anchoring process will enable us to devise strategies to prevent their attachment to the cell and thus block infection. During our studies to understand this attachment mechanism, we identified a membrane-associated enzyme responsible for cleaving a highly conserved motif within the anchor region of these surface proteins. Our results suggest that inhibition of this enzyme will prevent the proper attachment of most surface proteins resulting in nearly naked bacteria. Studies are in progress to both further define this enzyme and its role in the attachment process and to identify inhibitors, because such inhibitors may be considered a new class of antibiotic.
Capitalizing on the conservation of the anchoring process for surface proteins, we discovered that active polypeptides or proteins genetically fused to the common anchor regionof the M protein could be used to deliver the active molecule to the surface of gram-positive bacteria (i.e., for vaccine purposes). A number of proteins from a wide range of sources (bacterial, viral, human, parasites) have been engineered to be expressed on the surface of a human commensal bacterium (Streptococcus gordonii). When placed into the nasopharynx of mice, these recombinant bacteria remained there for up to 12 weeks. During that time the colonized mice produced antigen-specific serum IgG, salivary IgA and T-cell responses. We anticipate that this vaccine approach may be used for a variety of antigens to protect against invasion by disease organisms.
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Identification of a conserved region within the M protein of at least 30 different serotypes of group A streptococci enabled us to design experiments to determine if a vaccine comprising this region would protect against infection by multiple serotypes of streptococci. Using a mouse mucosal model of infection, we found that mice immunized intranasally with the M protein conserved region were protected from challenge by live streptococci of heterologous serotypes. This finding suggests that immunization with the conserved region can protect at the mucosa and may be the first step in designing an anti-streptococcal vaccine. Human studies are currently under way to test the protective efficacy of this approach.
Bacteriophage lytic enzymes:
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Bacteriophage (or phage) are viruses that infect bacteria. After infection, the virus directs the production of an enzyme that degrades the bacterial cell wall releasing the progeny bacteriophage to begin a new cycle. We purified one such enzyme from streptococci and used it to destroy streptococci directly. As little as 10 ng of enzyme is sufficient to destroy 10 million streptococci within seconds in vitro. When small amounts of enzyme were added to the oral cavity of mice that had been intentionally colonized with group A streptococci, the enzyme destroyed all the organism being carried by the mice. We thus have developed a non-antibiotic method to control bacteria that normally cause infection. Interestingly, these types of enzymes are very specific for the organism from which they came. For example, the streptococcal phage enzyme will kill group A streptococci but not other bacteria, particularly those normal bacteria found on the mucous membrane of humans. Thus, unlike antibiotics that kill many bacteria, phage lytic enzymes exhibit targeted killing, only destroying the disease organism. Since nearly all bacteria have phage systems, phage lytic enzyme may be developed for most pathogenic bacteria such as Streptococcus pyogenes, Streptococcus pneumoniae, and Staphylococcus aureus. These bacteria are found in up to 30% of the human nasopharynx without symptoms, which is the reservoir for these pathogens. By removing this reservoir from the population with phage enzymes, a significant impact on the dissemination of these organism for the initiation of disease could be realized. Our lab was the first to use this approach, and we are currently isolating phage enzymes for all the major pathogenic bacteria.