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Chapter 3 Observing Microbes through a Microscope

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1 Chapter 3 Observing Microbes through a Microscope
Biology 225: Microbiology Instructor: Janie Sigmon

2 Size of different cells/agents:
Our cells: mm (micrometer) Bacteria: mm Viruses: less than 100 nm (nanometer)


4 “Cells alive” animation
(View this animation to compare the sizes of different objects, animals, and microbes)

5 Light Microscopes Properties of light limit magnification/resolution to 2000X Brightfield (compound light) microscope Most common Field of view is bright; specimen is darker Least expensive Requires staining of specimens usually Staining requires killing organisms

6 Brightfield (compound light) microscope



9 Images of an amoeba and a paramecium taken with our microscopes modified with darkfield capabilities

10 Fluorescence microscope --http://micro. magnet. fsu


12 Picture of bacteria taken with a fluorescence microscope

13 Confocal microscopy Meningitis-causing bacteria. The tiny yellow dots are Neisseria meningitidis bacteria living inside human airway cells. Although they live in the noses and throats of many people without leading to disease, if they break through into the bloodstream they can cause potentially fatal meningitis and septicemia. (Confocal image by Shao Jin Ong.)

14 Confocal micrographic image of Bacillus anthracis;
cell walls appear green, while the spores appear red. Taken by CDC/ Dr. Sherif Zaki/ Dr. Kathi Tatti/Elizabeth White

15 Electron Microscopes Beware of artifacts
Staining techniques require expertise and $$$ Dehydration of specimen Placing specimen under vacuum Transmission electron microscope (TEM) Magnify 10,000-up to 500,000X View sections of organism Can see inside viruses/cells Scanning electron microscope (SEM) Magnify 1,000-10,000X See 3D image of structure


17 Under a high magnification of 12230x, this scanning electron micrograph (SEM) depicted some of the ultrastructural morphologic features displayed by this group of Gram-positive Micrococcus luteus bacteria. Taken by CDC/ Betsy Crane

18 This negative-stained transmission electron micrograph (TEM) depicts the ultrastructural details of an influenza virus particle, or “virion”. A member of the taxonomic family Orthomyxoviridae, the influenza virus is a single-stranded RNA virus. Taken by CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin

19 Scanned-probe microscopes
Can “see” molecules Expensive Used in research

20 Scanned-probe microscopy – Figure 3
Scanned-probe microscopy – Figure 3.11(a) is RecA (repair) protein from Escherichia coli and (b) is the O toxin from Clostridium perfringens.

21 The Gram staining technique

22 Acid-fast staining technique used to stain Mycobacterium leprae (bacteria responsible for leprosy)


24 The End

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