Effects of Lysogeny on an Oral Enterococcus faecalis Isolate

Objectives: Objectives: Lysogeny is an infective viral/bacterial relationship in which an infecting viral (phage) genome remains in a latent state within the infected (lysogenic) bacterial host cell. In most cases, the latent viral genome integrates into the host cell chromosome as a prophage. The presence of a prophage often confers new properties upon the lysogenic cell. Previously, we reported a high incidence of lysogeny among oral isolates of Enterococcus faecalis. The aim of this study was to learn whether lysogeny resulted in phenotypic modifications in an oral E. faecalis strain.

Methods: Methods: TUSoD11, a lysogenic strain of E. faecalis harboring the ΦEf11 prophage, was isolated from an infected root canal. A cured derivative of TUSoD11 in which the prophage was deleted, designated TUSoD11(△ΦEf11), was generated by allelic exchange mutagenesis and isolated by antibiotic selection. The two E. faecalis strains [TUSoD11 and TUSoD11(△ΦEf11)] were compared with respect to their ability to form biofilms and their sensitivity to a viral lytic enzyme. Biofilm formation by the two strains was assessed by means of a colorimetric microtiter plate assay based upon optical density measurement of crystal violet-staining of biofilms. A plate lysis assay (spot test) was used to detect the sensitivity of either strain to the lytic action of an endolysin produced by the phage during vegetative (productive) infection.
Results: Results: While both strains produced biofilms, the extent of biofilm production was 50.3% greater by the lysogenic strain (TUSoD11) compared to the cured derivative strain [TUSoD11(△ΦEf11)]. Furthermore, the cured strain was lysed by exposure to the phage endolysin whereas the lysogenic strain was resistant to the external application of the endolysin.
Conclusions: Conclusions: The data indicate that lysogeny alters the biofilm productivity and endolysin sensitivity of this oral E. faecalis strain.