The End Zone: Measuring Antimicrobial Effectiveness with Zones of Inhibition

[deleted-344495]

My daughter is working on this project for her science fair project. She followed all the steps and completed the process on Sunday the 14th. The only thing we couldn't do was use an incubator. Her science teacher told her that it would be fine and that the process should take about 3 days. We used 6 different products and 6 different petri dishes. Today is the 17th and we still haven't noticed any changes. There are no circles/zones of inhibition around around the filter discs. Not sure if we need to give it more time or what has happened.

[lynnsamuelson]

Thank you for asking the question. There are many things that can go wrong when culturing bacteria. First, did the untreated *control" plate grow colonies. If not, then then something went wrong in the set-up. You may want to work out a procedure to grow bacteria without the disinfectants first. This would be especially true if you are trying to grow the colonies without an incubator.

If you need further assistance please reply to this post.

Good Luck.

[deleted-290074]

Hi Carrie1977,

Like Lynnsamuelson mentioned, there are a lot of things that can go wrong when culturing bacteria. Did her bacteria grow at all? Did the bacteria not exposed to the compounds grow at all?

A lack of bacterial growth can be due to a multitude of problems, like the drying out of the agar due to nearby a heat source. Were the Petri dishes sealed well after being inverted? This helps keep the moisture from escaping. Without moisture the bacteria will die :'(. If she hasn't already, your daughter should ask her science teacher if he/she can provide her with "parafilm" to seal her dishes.

If the bacteria grew but the antibiotic just didn't seem to take effect, then your daughter may have not exposed the bacteria to the filter paper enough or saturated the filter paper in the antibiotics enough

Knowing more about how the Petri dishes look may help us offer more specific advice.

Good luck!

[deleted-288920]

Hi There,

Just to chime in with a few more questions:

What bacteria did she use?
What type of agar was used?
What antibiotic disks were used?

Thanks,
Nikki

[deleted-330540]

Hi!

I did this experiment but I used anti-bacterial soap, regular soap and hand sanitizer instead of disinfectants.

Everything went out fine and I got the zone of inhabitation; however, i measured the length of the zone not the width between the disc and bacterial colonies!!! :O I can't do it again because I won't have the equipment anymore!

WHAT DO I DO?

I measure it as the following picture.

Help! XtremeScience

[SciB]

Hi XS,

I'm not sure what you mean by 'length' in relation to a circle. If you measured the diameter of the entire zone then all you have to do is subtract the diameter of the disk and divide by two to get the width of the ZOI.

If this isn't what you did, then explain your procedure and we'll see if we can help.

Sybee

[deleted-288920]

Hi!

I couldn't see your picture, so I'm not exactly sure what you did. But to measure the zone you want to measure the diameter of the zone with the disk in the center, almost like a bulls eye or target. It is how I measure zones in my work.

Keep us posted!
Nikki