MadSci Network: Microbiology
Query:

Re: how do i grow bacteria?

Date: Sat Feb 23 13:56:37 2002
Posted By: Jim Caryl, Grad student, PhD Biochemistry & Molecular Biology, University of Leeds
Area of science: Microbiology
ID: 1014263175.Mi
Message:

Hi Vanessa

The addition of a flame to the incubation box serves as a rudimetary means of creating an anaerobic chamber (one with little ot no oxygen gas present), thereby allowing the culture of anaerobic bacteria. Anaerobes are bacteria that can't grow in the presence of oxygen (referred to as obligate anaerobes). You may also want to do similar cultures in the presence of air (oxygen) as there are also bacteria that do require oxygen to grow. There are also others who don't really mind and will survive if moved from an aerobic to anaerobic environment.

The petri dishes will need to be filled with a solid bacterial growth media. This is commonly an agar based media, which is a gelatinous polysaccharide extracted from seaweed. The agar solidifies and provides a solid support media in which essential nutrients and a carbon source are dissolved. You can either purchase essential bacterial growth nutrients separately, then mix with agar powder - or perhaps easier for you - purchase an "all-in-one" bacterial growth mix. A good place to get this is [Carolina Science & Math].

It is important to note that some bacteria are particularly fastidious (picky) about what they require, and it would be impractical for you to try and accomodate all their whims and nutritional desires. You will therefore require a non-selective media that is capable of supporting all but the most picky of strains. Good medias include Nutrient Agar, Blood Agar or Brain-Heart Infusion. Carolina conveniently supplies all in one kits of some of the above medias.

It is best if the petri dishes have their lids on. This prevents damage to the media and contamination with other bacteria. Remember that you are testing the bacteria on the hands - not what floats about in the air, dirt or random water droplets etc. Note that application of lids does not prevent oxygen getting into the petri dish - so don't worry that you'll kill your oxygen-requiring bacteria by applying the lid. It is however quite hard to maintain a truely anaerobic environment. You can purchase special packs that release hydrogen and carbon dioxide with the addition of water, or which you simply add to a tightly sealed box and react with (and remove) the oxygen in there. Again, I believe you could get these from Carolina S&M.

Finally, there are a few more things worth noting. Everything you do must employ aseptic technique. This means that anything that comes into contact with the bacteria and the media must be sterile (as must the media be, initially). After all, you are looking to evaluate skin microflora after washing with regular soap, and after anti-microbial soap - you don't want contamination from anywhere else.

A few questions for you to address in your study:

Will you use the same person's hands in the study? (different people tend to be colonised in slightly different ways, and in come cases with slightly different varieties of bacteria)

If so, how will you ensure that their hands (prior to washing) are equally colonised with bacteria prior to washing with either regular or antimicrobial soap?

Obviously washing with regular soap, taking a culture, then washing with anti-microbial soap and taking another culture will give you false results - as the final culture is bound to have the least colonies. You will have to think of a way of staggering the culture making.

Will you take a swab of the total palm or simply press a thumb or palm directly onto the media?

The anti-microbial soap you are using, is it bacteriostatic or bacteriocidal. The former merely inhibits bacterial growth (but doesn't kill), the latter kills. Therefore imagine that if it is bacteriocidal, yes it may inhibit growth on hands for a while, but when inoculated onto a plate (with no further inhibition from antimicrobial) they will grow as normal. If however it is bacteriocidal, then there will be no cells (theoretically) with which to form a colony.

One final thing. BE CAREFUL! The hands can pick up all kinds of "nasties" and by inoculating then onto a plate, you are amplifying their numbers and increasing the hazard. There will be a variety of different bacteria on the plates - you, I guess, will just be taking a total enumeration - but those individual colonies can only really be defined as nasty by an expert, so it is best to assume that they are all nasty. Make sure you wear latex (or vinyl) gloves when handling the inoculated plates, and when done, bag and autoclave before disposing of.

Hope this helps

Jim Caryl
MAD Scientist.


Current Queue | Current Queue for Microbiology | Microbiology archives

Try the links in the MadSci Library for more information on Microbiology.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-2002. All rights reserved.