Virulence characteristics of oral treponemes in a murine model

This study was designed to investigate the virulence characteristics of Treponema denticola, T. socranskii, T. pectinovorum, and T. vincentii following challenge infection of mice. These microorganisms induced well-demarcated, dose-dependent, raised subcutaneous (s.c.) abscesses which were similar in time of onset, lesion progression, and duration of healing. Only viable cells were capable of inducing these characteristic s.c. abscesses. Histological examination of the skin lesion 3 and 5 days postinfection revealed abscess formation in the s.c. tissues, and abundant spiral organisms were demonstrated to be present in the abscess. Host resistance modulation by dexamethasone (neutrophil alteration) and cyclophosphamide (neutrophil depletion) pretreatment had a minimal effect on the virulence expression by any of these treponemes. The T. denticola isolates demonstrated significant trypsin-like protease (TLPase) activity, while both T. socranskii and T. vincentii were devoid of this activity. Interestingly, T. pectinovorum strains were heterogeneous with respect to TLPase as high producers, low producers, and nonproducers. However, no differences in lesion formation were noted regardless of whether the species expressed this proteolytic activity or whether treatment with N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and dithiothreitol was performed. These results showed that (i) a murine model may be used to evaluate virulence expression by oral treponemes; (ii) while TLPase activity varies among the oral treponemes, this protease does not appear to participate in abscess induction in the mouse model; and (iii) T. pectinovorum strains show variation in TLPase activity.