How do I identify different bacteria on culture plates? Hello everyone,

[scilearner]

Hello everyone,

 

I'm very new to microbiology and does not have any background knowledge, so I have some simple questions on identifying different bacteria on agar plates. I have some questions and I have answered them the way I think. Please correct me where nessecary.

 

 

1. First of all what do all the lines in that plate mean, and how do you make a culture plate?

Ok so you get the agar medium, and dip a bacterial loop into your sample eg CSF and then streak them on agar plate. So I'm thinking those lines are bacterial streaks.

 

2. Now how do I know there is growth in the culture plate and what is the difference between streaks and circles in the above pic?

Do the circles mean bacterial colonies , then what do the streaks mean?I would like to see an agar plate where there is no bacterial growth, how does that agar plate look like, does it still have original

streaks, or would it just be the agar without any streaks.

 

3. Ok this is a picture of proper streaking and growth of H. influenzae on a CAP. Now how do I differentiate this bacteria from other bacteria capable of growing on choclate agar. Also my orginal pic is proper streaking and growth of N. meningitidis on a BAP, same question prevails for this.

 

 

4. Are bacterias able to grow on all agar types or do they have specific ones.

 

If anyone can answer thanks a lot in advance I'll post more pics depending on the replies.

[pluripotency]

Hello scilearner,

 

I am new to biology too, but I will attempt to answer your question from what I have learned. Someone more experienced should definitely confirm or correct my reply.

 

 

Streaking is a method by which you're allowing bacterial organisms the chance to form colonies. When you dip your cotton swab or whatever in your broth you have specimen in too high of a density for them to effectively form colonies. When you streak them along your agar plate, you're thinning out the population.

Think of an apartment with 40 people inside. These people cannot start families because there is simply not enough resources and space to multiply. When you spread them out over an apartment complex however, there is room in the refrigerator for food and spare bedrooms for cribs.

 

The streaks you are seeing are areas where the population density is too high. The circles are areas where population density is not affecting reproduction.

Here is a picture of a failed streak plate. Even after streaking, there was still no colonization by the organisms.

 

To answer your question about agar, I think that most bacteria can grow on agar medium (which is derived from seaweed). For some types of bacteria, there may be specialized agar which promotes colonization better but on that I am not sure.

 

I hope this helped!

 

 

 

[CharonY]

Agar is only a solidifier and it specifcally chosen as most bacteria cannot use it (and thereby degrade it). What allows them to grow is what else is in the medium. The selectivity of the medium can be rather low as in many complex media, or fairly selective.