Micro Lab 2: Ubiquity of Microorganisms, Culturing and Isolating Bacterial Colonies

Jump to Topics:
0:31 Learning Objectives
1:04 Ubiquity of Microorganisms
2:53 Experiment 1
4:09 Culturing Microorganisms
10:46 Experiment 2
12:09 Contamination, Aseptic Technique
13:48 Isolating Microorganisms
14:06 Colony Morphology
14:40 Experiment 3
16:59 Safety Guidelines
17:11 Observations and Interpretations
18:18 Escherichia coli & Micrococcus luteus Colony Morphologies
18:41 Preparation and Work Due
See the links below for more information related to the topics discussed in this video:
Culturing Microbes: • Culturing Microbes
Aseptic Technique: • Aseptic Technique
Textbook Information:
Openstax College, Rice University. (2016). Microbiology. Available for download at openstax.org/de....
Current and enrolled students should access the Moodle site for additional course materials.
This video is the property of Dawn Simms. All rights reserved. 2019.

[@yoshimorimoto4742]

This was super helpful!!! Thank you

[@ProfessorSimms]

You are very welcome :)

[@saurabhkardam4377]

I have a question, I am diluting the E.coli in Nutrient broth. at a particular dilution i am plating (spread plating) the E.coli. It gives appx 40 colonies on some plates but also gives a whole area coated type growth on other plate with same nutrient agar. Why it happens?

[@ProfessorSimms]

How are you inoculating? Are you using a precise amount of broth (i.e. are you using a micropipet to measure how much broth goes on each plate)? Are the plates with different results being inoculated, incubated, and counted at the same time with no discernible variables? Are you pulling from the top or bottom of the broth? Did you mix the broth prior to using it as an inoculum? All of these are things to consider when comparing plate counts, which is why I will often do this type of experiment in triplicate and take the mean colony number for each dilution factor

[@saurabhkardam4377]

@@ProfessorSimms 10 microlitre was the amount for inocculating. all plates were inoculated, incubated and counted at the same time. I am pulling the inocculum appx 0.5cm depth from the surface.
Actually, i am curious to know that is there any technical or microbiological reason for the problem which i stated? because i tried to keep everthing same for the control plates.

[@ProfessorSimms]

If the variability is not in the broth itself, it may be that the nutrient agar was not well mixed prior to plate pouring. It may also be that the cells were late in the growth stage, such that some cells were still dividing while others were entering death phase.

[@saurabhkardam4377]

@@ProfessorSimms thank you 🙂, are you on LinkedIn?

[@ProfessorSimms]

@@saurabhkardam4377 Yes, but I don't spend much time on there. RUclips is the best way to reach me, honestly.

[@sarahhaack3659]

How do you cool a sterile inoculating loop when using an agar plate ?

[@ProfessorSimms]

Lightly touch it on the edge of the sterile agar just inside the plate. Or, if you are inoculating a broth, dip the hot loop into the very top of the tube of sterile broth.

[@ErinRaciell]

Why not add the names of the different microbs that grow a different pH instead of just saying it?

[@ProfessorSimms]

This presentation was focused on ubiquity, physical types of media, aseptic technique, etc. For more information on microbial characteristics, nutritional requirements, and growing conditions, videos in my Micro Lecture and/or Pathogenic Micro Lecture playlists may be helpful.