Microorganisms are too small to be seen with the unaided eye and must be observed with a microscope
The word microscope comes from the Latin word "micro" (small) and the Greek word "skopos" (to look at)
Modern microbiologists use microscopes that produce magnifications ranging from ten to thousands of times greater than van Leeuwenhoek's single lens microscope
Helicobacter pylori is a spiral-shaped bacterium first seen in cadaver stomachs in 1886
Some microbes are more readily visible than others due to their size or observable features
Microorganisms must undergo staining procedures before their cell walls, capsules, and other structures lose their colorless natural state
Microorganisms and their components are measured in micrometers and nanometers
A micrometer (μm) is equal to 0.000001 m (10^-6 m) and a nanometer (nm) is equal to 0.000000001 m (10^-9 m)
Light microscopy uses visible light to observe specimens
A compound light microscope has a series of lenses and uses visible light for illumination
Total magnification of a specimen is calculated by multiplying the objective lens magnification by the ocular lens magnification
Resolution in microscopy refers to the ability of lenses to distinguish fine detail and structures
The resolving power of a microscope is influenced by the wavelength of light used
To achieve high magnification with good resolution, immersion oil is used with the objective lens
Darkfield microscopy is used to examine live microorganisms that are invisible in ordinary light microscopes or cannot be stained
Phase-contrast microscopy allows detailed examination of internal structures in living microorganisms without the need for fixing or staining
Differential interference contrast (DIC) microscopy uses differences in refractive indexes and two beams of light to produce brightly colored, nearly three-dimensional images
Fluorescence microscopy takes advantage of substances that absorb short wavelengths of light and emit light at longer wavelengths
Confocal microscopy is used to reconstruct three-dimensional images by illuminating one plane of a specimen at a time
Two-photon microscopy (TPM) uses long-wavelength light and requires two photons to excite the fluorochrome to emit light
Scanning acoustic microscopy (SAM) interprets the action of a sound wave sent through a specimen to study living cells attached to surfaces
Electron microscopy is used to examine objects smaller than about 0.2 μm, such as viruses or internal cell structures
In electron microscopy, a beam of electr
Electron microscopy is used to examine objects smaller than about 0.2 μm, such as viruses or the internal structures of cells
In electron microscopy, a beam of electrons is used instead of light
The resolving power of the electron microscope is far greater than that of other microscopes due to the shorter wavelengths of electrons
Electron microscopes are used to examine structures too small to be resolved with light microscopes
Images produced by electron microscopes are always black and white, but they may be colored artificially to accentuate certain details
Electron microscopes use electromagnetic lenses to focus a beam of electrons onto a specimen
There are two types of electron microscopes: transmission electron microscope (TEM) and scanning electron microscope (SEM)
Transmission Electron Microscopy (TEM)
In TEM, a beam of electrons passes through a specially prepared, ultrathin section of the specimen
The beam is focused on a small area of the specimen by an electromagnetic condenser lens
Scanning Electron Microscopy (SEM)
SEM provides three-dimensional views of specimens
In SEM, an electron gun produces a finely focused beam of electrons called the primary electron beam
The primary electron beam knocks electrons out of the surface of the specimen, and the secondary electrons produced are used to produce an image called a scanning electron micrograph
Scanned-Probe Microscopy
Scanned-probe microscopes use probes to examine the surface of a specimen usingelectric current
Scanned-probe microscopes can be used to map atomic and molecular shapes, characterize magnetic and chemical properties, and determine temperature variations inside cells