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

question 5

Short Answer

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?

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Definitions:

Resolution

The process of reducing or separating something into its components or the clarity and detail of an image.

Field Diameter

The apparent size of an area visible through the microscope lens, often measured in millimeters or micrometers.

Millimeters

A unit of length in the metric system, equal to one thousandth of a meter.

Iris Diaphragm

A thin, adjustable circular structure in optical devices or the eye that controls the amount of light passing through by changing its size.