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An immunogenic loop within the diphtheria toxin has been deleted from the B-subunit by a modification of the inverse polymerase chain reaction (IPCR) and replaced by a unique restriction endonuclease site. An oligonucleotide encoding an identified epitope sequence from the major outer membrane protein of Neisseria meningitidis of similar size and structure to that deleted has been introduced into the restriction site. Expression of the resulting chimeric B-subunit from Escherichia coli yielded a protein that was recognised by a panel of antibodies specific for the meningococcal epitope. Initial immunisation data suggest that this protein could elicit an antibody response against both diphtheria toxin and meningococcal proteins.

Variants of Chlamydia trachomatis in two Gambian villages with hyperendemic trachoma were analyzed by omp1-based polymerase chain reaction and sequencing from conjunctival swabs. Samples collected over a 22-month period included a complete cross-sectional study of each village. Overall, 4 genovar A and 4 B variants were characterized by point mutations in the omp1 gene, resulting in changes in the inferred amino acid sequence. Two genovar A and 2 B variants accounted for 87% of the total ocular chlamydial infection in both villages. Although some flux in the prevalence of individual variants was observed overtime, their overall distribution remained remarkably stable. There was no evidence of major antigenic shift arising from recombination events at the omp1 locus as described for genital tract infection. These results indicate that omp1 variation in these two trachoma-hyperendemic communities is limited and unlikely to hamper development of trachoma vaccines based on the major outer membrane protein.

Direct amplification of the major outer membrane protein (MOMP) gene by polymerase chain reaction (PCR) was used to identify Chlamydia trachomatis in eye swabs from clinically active cases of endemic trachoma in a Gambian village. Chlamydial DNA was detected in 51% of 96 subjects with clinically active disease and in 5% of 37 clinically negative individuals. The PCR detection was combined with typing, using nested primers to variable sequences (VS) 1, 2, and 4 of the MOMP genes to distinguish between trachoma genotypes A, B, and C, respectively. Genotypes A and B were detected in the village, with some individuals harboring both genotypes within the same eye. DNA sequencing revealed strain variants of both genotypes. Typing of genotype and strain variants is now in progress to study trachoma transmission within the village.