WEBVTT

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Clinically relevant bacteria are around

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one micron, which is one seventh
the size of a red blood cell.

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Because of this small size,
it may take some time and experience

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to be able to differentiate bacteria
from amorphous debris that occurs

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in many specimens.

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Caution should always be used
when working with biological specimens,

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as they all have
the potential to cause disease.

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Because of this, it is very important
to develop reliable sterile technique.

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Wet preps are used mainly to observe
live organisms and to get a quick idea

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of the organism size and shape,
and to determine their motility.

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To make the preparation, place
a drop of sterile water on a glass slide.

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Choose a colony of bacteria
from the plate with a sterile probe

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and touch it to the slide
next to the drop of water.

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Carefully mix the bacteria into the water

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to create a suspension
of the organism in the water.

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Some organisms are really sticky and hard
to remove from the probe in the water

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by touching the organism to the slide
and then mixing it with the water.

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It often emulsified more smoothly.

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If the area where the organism is mixed
is too small,

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the preparation may be too dense and
will be barely visible due to turbidity

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or the organism may be so crowded
that they will not be able to move around.

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In other words, you need to make sure
the area is large enough

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or the concentration is low enough
to be able to visualize

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individual organisms
and allow for movement.

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If the organism you are
preparing is in a broth culture,

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you can use a pasta pipette to obtain
a small amount to put on the slide.

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You may or may not need to add
water to the broth preparation.

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It just depends on the concentration
of organisms in the culture.

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With additional experience,
you will be able to judge

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how much material should be used
as you make the wet preparation slides.

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After making the suspension, gently
drop a cover glass onto the drawer.

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If you need to examine the specimen
for an extended period of time

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to prevent the drop

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from drying while examining it, use
a small amount of petroleum jelly

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on the edges of the cover glass,
and then place over the drop

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that the petroleum jelly can be spread
thinly on a paper towel

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with a tongue depressor,
and then drag the cover.

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Slip gently across it to get a thin line
on each edge of the cover.

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Slip.

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The slide is examined

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both at ten x and 40 x,
with a lowered condenser.

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Oil can't be used.