Use of lytic bacteriophage for Actinomyces viscosus T14V as a probe for cell surface components mediating intergeneric coaggregation.

A lytic bacteriophage for Actinomyces viscosus T14V (the reference strain for actinomyces coaggregation group A) was isolated from raw sewage. This phage, designated BF307, also lysed the T14V-derived nonfimbriated mutant PK455-2 as well as A. viscosus MG-1 and T14AV but not the other serotype 2 or serotype 1 strains of this species that were tested or any of nine Actinomyces naeslundii isolates. Phages BF307 belonged to Bradley morphological group C and was similar in appearance to the A. viscosus MG-1 phages Av-1 and Av-3, which do not productively infect A. viscosus T14V. A. viscosus MG-1 mutants selected for resistance to phage BF307, Av-3, or CT7 (a human dental plaque isolate with the same host range as BF307) were coresistant to the other two phages but sensitive to Av-1. These results indicate that the receptors on A. viscosus MG-1 for phages BF307, Av-3, and CT7 are identical or share a common precursor and that the receptor for phage Av-1 is distinct. Comparison of the genomes of BF307, Av-3, and CT7 revealed that their DNAs were similar in size but distinguishable by restriction analysis. Two altered coaggregation phenotypes were identified among the phage BF307-resistant mutants of strains MG-1, T14V, T14AV, and PK455-2. Class I mutants had lost the ability to interact with coaggregation group 1 streptococci, and class II mutants did not coaggregate with either group 1 or group 2 streptococci. These results are consistent with the proposal that the phage BF307 receptor on these A. viscosus strains is related to one of the structures that mediates coaggregation with oral streptococci. A model to delineate the various coaggregation mediators on the surface of actinomyces coaggregation group A cells is presented, and the use of these phages to probe surface components of human oral actinomyces strains is discussed.