Chapter 3 Observing Microbes through a Microscope

Biology 225: MicrobiologyInstructor: Janie Sigmon

Size of different cells/agents: Our cells: 10-100 mm

(micrometer)

Bacteria: 1-10 mm Viruses: less than 100

nm (nanometer)

“Cells alive” animationhttp://www.cellsalive.com/howbig

.htm

(View this animation to compare the sizes of different objects, animals, and microbes)

• 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

Light Microscopes

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

http://www.microbelibrary.org/Laboratory%20Diagnostics/details.asp?id=1345&Lang=English

Picture of bacteria taken with a fluorescence microscope

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.html%3Fimage%3D3&usg=__zTlEYvtXqctVN-_UY9Xgq5o8EU8=&h=406&w=406&sz=54&hl=en&start=7&sig2=E9fSpwqRIkS3fw0NrJFujQ&um=1&tbnid=PieK57ZmEF8T-M:&tbnh=124&tbnw=124&prev=/images%3Fq%3Dconfocal%2Bbacteria%26hl%3Den%26rlz%3D1T4ADBS_enUS329%26um%3D1&ei=knYuSoz8BuaClAe-iejSCg

Confocal microscopy

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 MicroscopesBeware of artifactsStaining techniques require expertise and $$$Dehydration of specimenPlacing specimen under vacuum

Transmission electron microscope (TEM)Magnify 10,000-up to 500,000XView sections of organismCan see inside viruses/cells

Scanning electron microscope (SEM)Magnify 1,000-10,000XSee 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 single-stranded RNA virus.

Taken by CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin

Scanned-probe microscopes

Can “see” moleculesExpensiveUsed 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)

THE END