1. Microorganisms

2. Definition of a Microorganism
Derived from the Greek: Mikros, «small» and Organismos, «organism»
Unicellular microscopic organism
Can exist in homgenous populations
Colonies
Can exist in heterogenous populations
Biofilms
Includes bacteria, fungi, viruses and protozoans

3. Micro_? Amino acid Optical microscope Electronic microscope Human eye
0.1nm nm nm nm 1 µm µm 100 µm 1 mm 1 cm
Atom
Amino
acid
Protein
Virus
Oganelle
Bacteria
Plant cell
Animal cell
Protists
Fungi
Ant

4. Microscopy
Staining

5. Stains Basic : Positively charged Acid : Negatively charged
Interacts with negative groups
Ex. Plasma membrane
Acid : Negatively charged
Interacts with positive groups
Ex. Glass

6. Positive Staining
Staining of the specimen

7. Negative Staining
Staining of the background
Large rod
Small rod

8. Method Simple Staining Single staining agent Basic or acid stain
Positive or negative staining
Allows to determine the size, shape, and grouping of cells

9. Cell Shapes Coccus: Spheres Division along 1,2 or 3 axes
Number of axes along which division occurs gives rise to different groupings
Typical groupings according to bacterial genus

10. The Cocci (Coccus) Axes of Division Grouping Diplococcus (2)
Streptococcus
(4-20)
Tetrade
(4)
Staphylococcus
(4-50)

11. Cell Shapes (Cont’d) Rods : Division is only along one axis
Typical groupings according to bacterial genus

12. Les Bacilles Axes of division Grouping Bacillus (1) Diplobacillus (2)
Streptobacillus
(4 -12)

13. 19th Century - Robert Koch
Observation:
Heaps of bacteria (colonies) of different sizes, colors, and shapes grow on potato slices exposed to ambient air
Colonies

14. Conclusion:
Colonies are pure cultures arising from single cells of different bacteria since a colony spread repeatedly generates identical colonies

15. Koch (Cont’d) Problem : Solution :
Several bacteria cannot grow on potatoes!
Solution :
Uses gelatin as a solidifying agent
Creates different solid media from liquids such as blood

16. Koch (Cont’d) Disadvantage of gelatin Solution – Agar
It is digested by several microorganisms
It is liquid at temperatures above 28oC
Solution – Agar
Polysaccharide derived from an algae
Remains solid at temperatures >37oC
Melts at 100oC
Is not digested by most bacteria

17. Conclusion:
Les colonies sont des cultures pures originaires de cellules uniques de différentes bactéries puisqu’une colonie étalée de façon répétée génère des colonies identiques

18. Mixed Cultures

19. Colony Morpholgies