THE NUMBER OF DIRECT REPEATS IN HAGA IS VARIABLE AMONG PORPHYROMONAS-GINGIVALIS STRAINS

The coding sequence for the surface protein hemagglutinin A (HagA) of Porphyromonas gingivalis 381 has previously been shown to contain four direct 1.35-kb repeats, designated rep,. This study was performed to determine if the number of rep(HA) units in hagA is consistently 4 or if allelic polymorphism exists among strains and/or upon multiple pass age of P, gingivalis, To this end, primers which were homologous to th e regions directly 5' and 3' of the repeat domain in hagA were synthes ized. PCR conditions which allowed amplification of the 8.4-kb repeat region between the primers in P, gingivalis 381 were established. Geno mic DNA templates from 13 other P, gingivalis strains and 9 fresh clin ical isolates from patients were analyzed under the same conditions as used above. Analysis of these PCR products demonstrated that the stra ins tested had different numbers (two to four) of rep, units in the re spective hagA genes, The PCR products of 8.4, 7.0, and 5.7 kb represen t four, three, and two repeats, respectively, One strain from each gro up (381, four repeats; W83, three repeats; and AJW4, two repeats) was also tested to determine if the number of repeats remained invariant u pon passaging onto solid medium, No variability in the number of repea ts in hagA within a strain was detected after 18 passages. P, gingival is 381 was chosen for further testing in a mouse abscess model to dete rmine if conditions of in vivo growth would select for deletions or du plications of the repeated sequences. Five days after infection, no ch ange in the number of repeats was detected in cells recovered from eit her nonimmunized or preimmunized mice. This data indicates an interstr ain variability of the number of repeat units and hence a size variabi lity of the HagA protein of P, gingivalis, but unlike some surface ant igens of other pathogenic species, the number of repeats remains relat ively stable given the conditions of growth tested here.