NEGATIVE STAINING

NEGATIVE STAINING

Negative staining provides a more detailed assessment of a microbe’s morphology and helps prevent any distortion of the mi- crobe’s ultrastructure by the staining procedure. It also makes the outline of the cells highly visible. Nigrosin and bacterial cells are negatively charged. Therefore, negative staining works because like charges repel each other, preventing the cells from taking up the stain.

PROCEDURE

Note: If you are keeping a lab notebook, record the date, time, and experiment title on a fresh page before you begin.

1. Over a sink or disposable plastic container, place 1 – 2 drops of nigrosin near the end of one of the “Negative” slides.

2. Sterilize your inoculation loop with your candle.

A. Pour 70% isopropyl alcohol into a 100 mL beaker to a depth of 2 – 4 cm. Place the cap back on the bottle, and position it

far out of the way.

B. Light your candle, and set it aside. Be very cautious that your candle is safely positioned away from the beaker of isopro-

pyl alcohol.

C. Dip the inoculation loop into the isopropyl alcohol for 10 seconds. Once you’ve put the inoculation loop in the alcohol,

keep it angled down so that no alcohol drips back onto your hand.

D. Without touching the inoculation loop to anything, carefully pass the end of the inoculation loop through the flame several

times.

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