No abstract

Streptococcus pneumoniae is an important pathogen that causes disease in young and elderly individuals. The currently available polysaccharide vaccines have limited efficacy in those age groups most susceptible to pneumococcal infections. This study focuses on mapping the epitopes of a surface protein of S. pneumoniae by biopanning a 15 mer phage display library using 5 different monoclonal antibodies (MAbs) against the Pneumoccal surface adhesin A (PsaA). PsaA is a component of the bacterial cell wall that is highly species specific and is involved in bacterial adherence and virulence. Biopanning of the phage display library reveals three distinct epitopes on the PsaA protein. The sequence homology of these epitopes ranges from two to six amino acids when compared to the native PsaA protein type 2. Two of these epitopes have been evaluated for their immunogeneicity in mice. The peptide selected by the MAbs 8G12, 6F6, and 1B7 is referred to as the consensus peptide and is immunogenic in mice. Optimal anti-PsaA response is observed in mice immunized with 50microg of the consensus peptide complexed to proteosomes in 1:1 ratio. The anti-PsaA response is significantly lower than the response to the PsaA native protein. The peptide selected by monoclonal antibody 4E9 in its lipidated form is significantly protective in mice challenged with S. pneumoniae serotype 2 when compared to mice immunized with the native protein. These results show that the selected epitopes of PsaA protein are immunogenic and protective in mice. These epitopes need to be evaluated further as alternatives to currently available vaccines.

Major protein-containing antigens of Legionella pneumophila serogroup 1 were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis with rabbit antisera to 14 different Legionella species or serogroups. Fourteen bands were observed in immunoelectropherograms of whole-cell, sonicated cell, and heated cell preparations, seven of which appeared in the supernatant fluid from the heated cells and three of which were shown in an outer membrane fraction. Immunoblots of whole-cell antigen preparations of 14 Legionella species or serogroups revealed seven major Legionella proteins: antigens with molecular weights of 58,000, 79,000, and 154,000 were present in all Legionella sp. strains, antigens with molecular weights of 44,000 and 97,000 occurred in multiple species, and antigens with molecular weights of 14,000 and 25,000 were present only in L. pneumophila strains. All sera from 15 patients with cultureconfirmed L. pneumophila serogroup 1 disease and 14 of 18 (78%) sera from serologicaily diagnosed patients reacted with the 58-kilodalton (kDa) common antigen. In contrast, less than one-half of the sera reacted with the L. pneumophia-specific proteins (14 and 25 kDa). Absorption of sera with Escherichia coli cells had no effect on their reactivity with the 58-kDa antigen, whereas absorption with L. pneumophila serogroup 1 cells removed reactivity. These data suggest that the 58-kDa antigen may prove useful in serodiagnostic tests for legionellosis.

Confirmation of a culture as Legionella when it is unreactive with available serologic reagents involves tests that are impractical in most clinical laboratories. A nucleic acid probe that hybridizes only to members of the genus Legionella was recently prepared for marketing by Gen-Probe, Inc., San Diego, Calif. We tested 215 Legionella strains, representing 22 species, and 84 non-Legionella strains, representing 17 bacterial genera, with the Gen-Probe kit. All but four Legionella strains (L. bozemanii, <2 % of total) and no heterologous strains gave positive test results. We conclude that the Legionella gene probe is a valuable addition to existing diagnostic tests for Legionella organisms.

Gene htpB, which encodes the 58-kilodalton protein of Legionella pneumophila, was cloned in Escherichia coli and its complete nucleotide sequence was determined. Analysis of this sequence revealed an open reading frame of 1,644 nucleotides encoding a protein with a predicted molecular mass of 57,952 daltons. Data obtained by amino-terminal sequencing of the purified 58-kilodalton protein agreed, except for one amino acid residue, with the predicted amino acid sequence, identifying this open reading frame as htpB. A comparison of the primary structure of this protein to other proteins of similar molecular weights from E. coli, Mycobacterium leprae, M. tuberculosis, and Coxiella burnetii revealed significant regions of sequence similarity, which are discussed.