Any microbiologists out there?

angeldelight

Ok, I'm doing a micro write-up and there's a Q "What is the difference between a liquid and a solid medium?" Can anyone help me out with the answer? I know one has agar and the other doesn't but I presume they're asking for more than that?

GuanYin

angeldelight wrote:

Ok, I'm doing a micro write-up and there's a Q "What is the difference between a liquid and a solid medium?" Can anyone help me out with the answer? I know one has agar and the other doesn't but I presume they're asking for more than that?

Technically the difference is agar, but if they want to know the purposes then
liquid medium (broths) gives you faster growth and provides a uniform solution of motile bacteria that can be used to streak plates or in infection/growth assays. For visualisation, the bacteria grown in broths will display characteristics (alignment, clustering etc) that can't be seen easily with solid grown bacteria. Solid media (Agar) is used to evaluate viability (colony forming units) or to isolate identical clones of a bacteria (which is what a colony is) - for instance, bacteria that are resistant to an antibiotic.

Capt'n Midnight

If there are a variety of microbes then solid media can be used to separate them since colonies of different types can have different colours etc.

For the purposes of isolation from a sample you can use "dilute" by putting streaks on one edge of the dish and then flame the hoop and touching the frist streak make a second set and then flame again and from the second a third set, you can't do this with homegoneous liquid medium. This also gives a very rough order of magnitude idea of the microbe level in the original sample since if too dilute few colonies form.

Liquid media is usually better for production scale growth because by definition solid media reduces the volume available, though for aerobes you need a way of aeration.

John

Liquid media also allows you to observe bacterial movement which isn't possible on solid media.

Dr. Dec

Capt'n Midnight wrote:

Liquid media is usually better for production scale growth because by definition solid media reduces the volume available, though for aerobes you need a way of aeration.

Liquid medium for microbes is generally used in bioreactors. For aerobic growth there are all kinds of crazy ways of introducing gasses to your reaction mixture. But in general you have a sparger which releases bubbles at the bottom of the reaction chamber.

Though it might be out of the scope of your answer, liquid media can be used to grow animal cells in culture. This is hugely different to growing prokaryotes though.

angeldelight

Thank you all for replying got full marks on that write up. Doing another one tonight tho so stay posted :P only messing, thanks again