Characterization of an inducible bacteriophage from a leukotoxic strain of Actinobacillus actinomycetemcomitans.

A bacteriophage, designated phi Aa17, was isolated by mitomycin C induction from leukotoxic Actinobacillus actinomycetemcomitans strains 651. Electron microscopy of the virus revealed particles with regular, nonelongated, polyhedral heads, and tails consisting of a contractile sheath and core. Spikes emanated from the base of the tail. The head had a diameter of 70 nm. The fully extended tail sheath had a length of 127 nm and a diameter of 22 nm. In its contracted form, the tail sheath measured 47 nm in length and 25 nm in diameter. The phage had a buoyant density of 1.370 in CsCl, and its genome was found to be double-stranded DNA. A single-cycle growth curve revealed that the phage had a latent period of 30 min and a burst size of 435 PFU per cell. The host range of the phage was examined, and A. actinomycetemcomitans strains ATCC 29523 and ATCC 29524 were found to be phage sensitive, whereas strains Y4, ATCC 29522, 2043, 652, 651, 627, 2097, N27, 2112, and 511 were resistant. The host range of this virus does not suggest any association between the phage and leukotoxin production.