Chapter 3
Observing Microbes through a Microscope
Biology 225: Microbiology
Instructor: Janie Sigmon
Size of different cells/agents:



Our cells: 10-100 mm
Bacteria: 1-10 mm
Viruses: less than 100 nm
(micrometer)
(nanometer)
“Cells alive” animation

http://www.cellsalive.com/howbig.htm
(View this animation to compare the sizes
of different objects, animals, and
microbes)
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
Brightfield (compound light) microscope
Images of an amoeba and a paramecium
taken with our microscopes modified
with darkfield capabilities
Fluorescence microscope -http://micro.magnet.fsu.edu/primer/java/lightpaths/fluorescence/fluorolightpathsjavafigure1.jpg
Picture of bacteria taken with a fluorescence microscope
http://www.microbelibrary.org/Laboratory%20Diagnostics/details.asp?id=1345&Lang=English
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.)
http://images.google.com/imgres?imgurl=http://www.wellcome.ac.uk/en/wia/images/3.jpg&imgrefurl=http://www.wellcome.ac.uk/en/wia/gallery.ht
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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
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
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
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 singlestranded RNA virus.
Taken by CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin
Scanned-probe microscopes
Can “see” molecules
Expensive
Used in research
Scanned-probe microscopy – Figure 3.11(a) is RecA (repair) protein
from Escherichia coli and (b) is the O toxin from Clostridium perfringens.
The Gram staining technique
Acid-fast staining technique used to stain Mycobacterium leprae (bacteria
responsible for leprosy)