Restriction site polymorphism in genes encoding type 2 but not type 1 gonococcal IgA1 proteases

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

Neisseria gonorrhoeae IgA1 proteases share epitopes recognized by neutralizing antibodies

The antigenic diversity among IgA1 proteases of 61 Neisseria gonorrhoeae strains isolated during a period of 23 years and on four continents was examined in enzyme neutralization assays employing rabbit antisera raised against selected IgA1 proteases. The antigenic analyses were compared with results of iga gene-region RFLP patterns and enzyme cleavage specificity for substrate IgA1. Type 1 IgA1 proteases were antigenically uniform while six different antigenic types were detected among type 2 enzymes. Extensive cross-reactions of antibodies against the different antigenic types suggested only minor differences in relevant epitopes. Epitopes previously found to be common to all Neisseria meningitidis IgA1 proteases were also shared by all N. gonorrhoeae IgA1 proteases in the collection. Human sera from patients with gonorrhoea showed broadly cross-reactive neutralizing activity at titers comparable to those of sera from immunized rabbits. In conclusion, N. gonorrhoeae IgA1 proteases show a remarkable lack of diversity of epitopes recognized by enzyme-neutralizing antibodies. If future studies confirm that cleavage of IgA1 is an important step in gonococcal infections, Neisseria IgA1 proteases may be attractive vaccine candidates.

Antigenic relationships among immunoglobulin A1 proteases from Haemophilus, Neisseria, and Streptococcus species

To investigate the antigenic variation and relationships of immunoglobulin A1 (IgA1) proteases among different species and genera, we examined a comprehensive collection of serine type and metallo-type IgA1 proteases and corresponding antisera in enzyme neutralization assays. Sharing of neutralizing epitopes of metallo-type IgA1 proteases from Streptococcus pneumoniae, Streptococcus sanguis, Streptococcus mitis, and Streptococcus oralis and of serine type IgA1 proteases from Haemophilus and pathogenic Neisseria species was extremely limited. A number of limited to strong cross-reactions in such epitopes were found among serine type IgA1 proteases released by members of the genera Haemophilus and Neisseria, reflecting the common origin of their iga gene. However, the relatively limited prevalence of shared "neutralizing" epitopes of IgA1 proteases from the two genera indicates that they rarely induce immunity to each other. In contrast, extensive sharing of neutralizing epitopes was found between N. meningitidis and N. gonorrhoeae IgA1 proteases, making them potentially attractive vaccine components. Among metallo-type IgA1 proteases, several pneumococcal proteases were found to induce neutralizing antibodies to IgA1 proteases of oral streptococci whereas the opposite was not the case.

Molecular polymorphism and epidemiology of Neisseria meningitidis immunoglobulin A1 proteases

Neisseria meningitidis is one of several important bacterial pathogens that secrete a specific protease capable of cleaving human immunoglobulin A1 (IgA1) in the hinge region. To obtain further information on this putative virulence factor, we examined the IgA1 protease and iga gene region of 133 isolates of N. meningitidis assigned to 88 multilocus enzyme genotypes and representing major epidemics and carrier strains from 19 countries. Of the two IgA1 cleavage specificities previously observed, isolates associated with epidemics of meningococcal disease showed exclusively type 1 IgA1 protease activity. Considerable heterogeneity of the N. meningitidis IgA1 protease was demonstrated at both the protein and gene levels. Thus, five different forms of IgA1 protease were detected with enzyme-neutralizing antibodies raised in rabbits. An antiserum raised against a single type 2 IgA1 protease inhibited the enzyme activity of all strains examined, a finding of potential significance for the possible application of IgA1 protease in a vaccine against meningococcal disease. Examination of the iga gene region with restriction endonucleases revealed a high degree of polymorphism among strains belonging to some multilocus enzyme genotypes. The different iga gene types did not correlate with cleavage type or inhibition of the IgA1 protease. Our findings indicate that horizontal genetic exchange occurs in vivo with considerably different frequency in different clones of meningococci.