Actinobacillus actinomycetemcomitans (Aa) strain ST1 carries the tetracycline (Tc) resistance transposon Tn916 and the Aa phi ST1 prophage, which is closely related to temperate bacteriophage Aa phi 23. High titre phage preparations were obtained from this strain by mitomycin C induction and were used to transduce the TcR determinant to the TcS recipient strains ZIB1001 and ZIB1015 (MIC 2 micrograms Tc/ml). TcR transductants (MIC > or = 32 micrograms Tc/ml) were detected at frequencies of 3 x 10(-6) to 5 x 10(-8) per pfu. All TcR transductants examined contained the entire Tn916 inserted at several different locations within the Aa genome. They appear to have resulted from generalized transduction. In addition both bacteriophages, Aa phi 23 and Aa phi ST1, were capable of transducing the chloramphenicol (Cm) resistance marker of plasmid pKT210 (transduction frequencies of 2 x 10(-5) to 3 x 10(-7) per pfu) to the recipient strain ZIB1001 (MIC 8 micrograms Cm/ml). Eleven CmR ZIB1001 transductants (MIC > or = 100 micrograms Cm/ml) studied carried a plasmid indistinguishable from pKT210 by restriction analyses. In view of the high prevalence of this phage family, and the increasing use of tetracycline in periodontitis therapy, these findings may have clinical importance.

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 Aa phi 23. Only 6 of these 14 strains had produced lysis or single plaques on suitable indicator strains. Phage Aa phi 247 derived from one of these lysogens was indistinguishable from Aa phi 23 by electron microscopy, and the genomes showed highly related DNA hybridization patterns. The remaining 20 isolates exhibited hybridization patterns very different from that of Aa phi 23 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 Aa phi 23-related prophage correlated with serotype a and AP-PCR type 1 of the bacterial host. This may indicate that Aa phi 23 and related phages have a limited host range.

The DNA of the temperate bacteriophage Aaphi23 isolated from the oral bacterium Actinobacillus actinomycetemcomitans was examined structurally both in the phage head and in the prophage. The DNA in phage particles comprises 44 kb linear molecules with a terminal redundancy of 1.6 kb, which represent circular permutations. Thus, DNA is packaged into phage heads by the headful mechanism. The Aaphi23 prophage is integrated into the host chromosome.