Table 74
the Results Below Were Obtained from a Use-Dilution Test

Table 7.4
The results below were obtained from a use-dilution test of two disinfectants. Cultures were inoculated into tubes with varying concentrations of disinfectants and incubated for 24 hr at 20°C, then subcultured in nutrient media without disinfectants.(+ = growth; - = no growth)
$\quad\quad\quad\quad\quad\quad\quad\quad\text { Disinfectant } 1$$\quad\quad\quad\quad\quad\text { Disinfectant } 2$
$\begin{array}{rcccc}\text { Concentration } & \text { Initial } & \text { Subculture } & \text { Initial } & \text { Subculture } \\1: 10 & - & + & - & - \\1: 90 & + & + & - & - \\1: 900 & + & + & - & - \\1: 90,000 & + & + & - & - \\1: 900,000 & + & + & - & + \\1: 9,000,000 & + & + & - & +\end{array}$ In Table 7.4, what is the minimal bacteriostatic concentration of each disinfectant? Which compound is bactericidal? At what concentration?