Biology Investigation Ideas!

[pauliwauli2]

I'm doing AH biology (around the same level as A levels for those in England) and I have to do a practical investiagation. It has to take place within the school so obviously the opportunities are limited.

I'm really interested in medicine etc., and was thinking about growing plaque in a petri dish and then testing different mouth washes on it to see which is most effective... Does anyone know if there is any way of growing plaque in a petri dish?

[sddsddean]

Don't know about plaque in particular, but could you not do something like not brush your teeth for a day, take a swab of them and see what grows in the agar (or whatever in the petri) and see how effective mouth washes are against your own 'germs'.

[theprof]

I'd like to start by saying well done for considering plaque as a practical investigation for the purpose of your course. You're showing talent that wouldn't go amiss in some freshers nowadays, although not at my uni I hasten to add!

Dental plaque is nowadays regarded as a biofilm. What's a biofilm? Well this may be defined as a collection of bacterial communities attached to a surface which are embedded in bacterial and host polymers.

Now as you know, dental plaque contains from hundreds to thousands of different species of bacteria and fungi depending on the general oral health of the person from whom the sample was taken. These bacteria in situ are locked into a matrix of polymers, fructans and glucans that are synthesised by the bacteria themselves.

Predominant bacteria include Streptococcus mutans, Capnocytophaga species, Lactobacillus, gram-negative rods etc. These bacteria do demonstrate differing sensitivity to oral antiseptics such as chlorhexhidine gluconate, thymol, hexetidine and cetylpyridium chloride.

(continued)

[theprof]

Your first step is to sit down and think carefully with the advice of your teachers/lecturers how you are going to set up the experiment. Now before we go any further, you need to accept that the equipment, instrumentation, chemicals and culture media available to you will not be up to the standard of a university, so you'll have to confine yourself to the stuff you've got available.

Oral plaque can be cultured in vitro and there are lot's of specifically designed growth media available. In your case, I suggest you try to get hold of a readily available media called Peptone Yeast Extract which will grow a fair amount of oral bacteria. Another media called BMM, which is a mucin containing analogue of PYE would work even better. You need a semi-solid media for a petri dish and agar would be a suitable inert additive although there are others. Suitable "recipes" for Agar/PYE mixtures are readily available in laboratory manuals, but remember that you need a semi-solid gel rather than a broth. You also need to add about 5% sucrose to the media during formulation to mimic the oral environment

(continued)

[theprof]

The lab technicians should have the necessary skill to streak the culture plates or show you how to do it. Follow all aseptic techniques.Try incubating some plates at 37 degrees Celsius for 24 hours to see if body temperature would increase the size of the colony. Let other culture plates remain at room temperature.

Gram-negative rods would be a suitable group to concentrate on amongst the plates as chlorhexhidine etc have a measurable effect upon them and they are readily identifiable with a light-microscope. Try different concentrations of mouthwash solutions. Forget species identification, it would be beyond the facilities you have available, typically involving CLSM electron microscopy.

One tip I can give you is to pay special attention to Listerine. This mouthwash kills a vast number of bacteria of all types and is analogous to bleach as far as the mouth is concerned. In fact, Listerine is currently the favoured wound antiseptic in many military field hospitals worldwide.

Finally, your school may have online access to the hundreds of microbiology journals which will help you to see how such studies are laid out professionally. They all generally follow a common format and if you can write your study in a similar manner, it will show you are able to write papers to a high and consistent standard. This will go far with the readers of your paper.

[theprof]

Let me know if I can help further.