Occurrence of temperate bacteriophages in different Actinobacillus actinomycetemcomitans serotypes isolated from periodontally healthy individuals

The occurrence of temperate bacteriophages was studied in 34 isolates of Actinobacillus actinomycetemcomitans derived from 27 periodontally healthy Finnish individuals both by lysis/plaque assays and by DNA hybridizations. In addition the serotype, the ribotype and the arbitrarily primed polymerase chain reaction (AP‐PCR) profile were determined for each A. actinomycetemcomitans strain. Fourteen isolates showed hybridization patterns very similar to that of a known lysogen when probed with the genome of the previously characterized temperate phage Aaø23. Only 6 of these 14 strains had produced lysis or single plaques on suitable indicator strains. Phage Aaø247 derived from one of these lysogens was indistinguishable from Aaø23 by electron microscopy, and the genomes showed highly related DNA hybridization patterns. The remaining 20 isolates exhibited hybridization patterns very different from that of Aaø23 DNA. Seven of these strains also gave lysis or single plaques, suggesting that 21 of the 34 strains were lysogenic. These data indicate that the prophages per se do not represent a virulence factor exclusively associated with periodontal disease. Presence of an Aaø23–related prophage correlated with serotype a and AP‐PCR type 1 of the bacterial host. This may indicate that Aa(J)23 and related phages have a limited host range.