The sublethal concentration of zoocin A determined for each strain is given in Table 1. The growth assay proved simple and highly reproducible. Although somewhat arbitrary, setting the lag phase cut off point at initial OD+0.1 yielded highly reproducible experimental data. Determining the growth rate constant did not allow us to reliably distinguish treated from untreated cultures. Once treated cultures reached log phase, they grew as fast as untreated cultures, suggesting that once the cells have repaired their peptidoglycan and degraded any remaining intracellular PS-ODN, there were no remaining constraints to cellular growth. The addition of 0.1 μg mL−1

VX-809 mouse zoocin A and 10 μM of either FABM or FBA to S. IGF-1R inhibitor mutans OMZ175 resulted in a lag phase that was significantly longer (P=0.001) than that observed for the addition of zoocin A alone (Fig. 1). The effect of zoocin A and FABM on S. mutans OMZ175 growth was dose dependent. In the absence of zoocin A, FABM (1–20 μM) had no significant

effect on S. mutans OMZ175 growth (Table 2). When combined with 0.1 μg mL−1 zoocin A, the lag phase increased proportionally (R2=0.9928) with increasing FABM concentration. Similarly, using a fixed concentration of FABM (10 μM), the increase in lag phase was proportional to the zoocin A concentration (Table 2) both in the presence (R2=0.9919) and in the absence (R2=0.9069) of the PS-ODN. Growth inhibition was target specific. Only S. mutans strains were severely inhibited in the presence of FABM, whereas all streptococcal strains except S. oralis were severely inhibited by FBA (Table 3). Streptococcus

oralis 34 does contain the FBA target sequence within its genome but is not sensitive to zoocin A. Compared with growth in the presence of zoocin A, there were large increases in the lag phase (between 25% and >134%) for all S. mutans strains Adenosine triphosphate grown in the presence of zoocin A plus FABM. With the exception of S. oralis 34, compared with growth in the presence of zoocin A, there were large increases in the lag phase (between 30% and >134%) for all streptococcal strains grown in the presence of zoocin A plus FBA. Streptococcus sobrinus 6715 and S. sanguinis K11 showed no response to either FABM or FBA used at concentrations of 10 μM, but both showed significant (P=0.001) increases in lag phase in the presence of zoocin A plus 50 μM FBA. There were some strains that showed a small (<11%) but statistically significant increase in lag phase when incubated with the ATS control, suggesting a degree of nonspecific toxicity by these constructs. As a consequence of their high GC content, negative charge and or sulphur group, PS-ODN have been reported to interact with cellular proteins Brown et al., 1994), resulting in nonspecific toxicity (Chrisey et al., 1995; Stein, 1996).