Table 75
the Following Results Were Obtained from a Use-Dilution Test

Table 7.5
The following results were obtained from a use-dilution test of two disinfectants. Cultures were inoculated into tubes containing varying concentrations of the disinfectants, incubated for 10 min. at 20°C, and then transferred to growth media without disinfectant. (+ = growth; - = no growth)
$\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\text { Disinfectant A }$
$\begin{array}{rcc}\text { Concentration } & \text { Gram-positive bacteria } & \text { Gram-negative bacteria } \\1: 10 & - & - \\1: 20-70 & - & + \\1: 80 & + & + \\1: 90 & + & + \\1: 100 & + & + \\1: 110-500 & + & +\end{array}$

$\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\text { Disinfectant B }$
$\begin{array}{rcc}\text { Concentration } & \text { Gram-positive bacteria } & \text { Gram-negative bacteria } \\1: 10 & - & - \\1: 20-70 & + & + \\1: 80 & + & + \\1: 90 & + & + \\1: 100 & + & + \\1: 110-500 & + & +\end{array}$ In Table 7.5, which disinfectant is most effective? Against which group of bacteria is Disinfectant A most effective?