What is the difference between a wet mount and a hanging drop preparation?
Question
The other day, someone asked me what the difference is between a wet mount and a hanging drop prep in microbiology. I had a rough idea but decided to dig into it properly. Wet mounts are quick and easy, great for basic observations. Hanging drops take longer to prep but let bacteria swim around more naturally. This breakdown really helped me understand it.
Answer ( 1 )
Wet mount
A wet mount is a quick drop of liquid culture or water suspension on a slide covered by a coverslip. The thin film flattens the cells and they are squeezed between glass surfaces. Evaporation can dry the prep in minutes.
Hanging drop
In a hanging drop you place the drop on a coverslip, invert a concave (depression) slide over it and seal the edges with Vaseline. The drop now hangs freely into the cavity, leaving a deeper pool with more oxygen and room for the microbes to swim.
When to use which
Use a wet mount for yeast budding, algae, or quick check of urine sediment. Use a hanging drop when you want to confirm bacterial flagellar motility, watch protozoa swim, or keep the sample alive longer.
Little caution
Both methods are unstained so the condenser iris must be closed to get contrast, and because the specimens are alive you must treat the slide as biohazard afterwards.
Main differences
• Motility: Hanging drop shows true directional motility because the cells are not squashed. Wet mount often shows Brownian motion only.
• Drying: Hanging drop lasts longer, sometimes hours, wet mounts dry fast, so you must work quickly.
• Depth of field: Hanging drop has greater depth, so you can focus up and down through the drop. Wet mount is almost two-dimensional.
• Ease: Wet mount needs only a slide and coverslip. Hanging drop needs a concave slide and petroleum jelly, takes more time.