Viewing the Microbial World

• Metric units are used to express the sizes of microbes
• Meter (m) is the basic unit of length in the metric system, equivalent to 39.4 inches
• Micrometer (μm) is one millionth of a meter, used to express the sizes of bacteria and protozoa
• Typical spherical bacterium (coccus) is approximately 1 μm in diameter
• Typical rod-shaped bacterium (bacillus) is approximately 1 μm wide x 3 μm long
• Nanometer (nm) is one billionth of a meter, used to express the sizes of viruses
• Sizes of viruses that cause human diseases are 10 to 300 nm
• Ebola virus are as long as 1,000 nm (1 μm)
• Ocular micrometer is used to measure the sizes of microorganisms under a microscope
• 0.001 μm = 1 nm
• 1,000,000,000 μm = 1 km
• 10,000,000,000 nm = 10 m
• 0.01 cm = 100 μm
• Microscope is an optical instrument used to observe tiny objects that cannot be seen with the unaided human eye
• Microscope: Magnifying power - how much larger a given lens can make an image appear; Resolving power - how far apart two adjacent objects must be before a given lens shows them as discrete entities; Contrast - ability needed to distinguish detail between adjacent objects
• Resolving power of the unaided human eye is approximately 0.2 mm
• Robert Hooke first used a microscope in 1667
• Antonie van Leeuwenhoek used a single-lens microscope and observed "animacules" in 1675
• Zaccharias Jansen invented the first compound microscope in 1600's
• Joseph Jackson Lister developed a significantly better microscope in 1830
• Simple microscope contains only one magnifying lens, such as a magnifying glass
• Leeuwenhoek's simple microscopes had a maximum magnifying power of about x300
• Compound microscope contains more than one magnifying lens, also referred to as a compound light microscope
• Compound light microscope usually magnifies objects about 1,000 times
• Resolving power of a compound light microscope is approximately 0.2 μm, about 1,000 times better than the resolving power of the unaided human eye
• Objects cannot be seen if they are smaller than half of the wavelength of visible light (~0.45 μm)
• Magnifying lens systems in a compound microscope: Eyepiece or ocular lens (usually x10), Objective lens (x4, x10, x40, and x100 are the four most commonly used)
• Parts of a microscope: Mechanical parts for support and adjustment, Magnifying parts for enlargement of the observed specimen, Illuminating parts for light provision
• Mechanical parts: Base, Arm, Stage, Inclination joint, Body tube, Draw tube, Revolving nosepiece, Dust shield, Coarse adjustment knob, Fine adjustment knob, Slide movement knobs
• Illuminating parts: Condenser, Iris Diaphragm, Light Source
• Magnifying parts: Eyepiece/ocular, Scanning objective (4X), Low power objective (LPO, 10X), High power objective (HPO, 40X), Oil immersion objective (OIO, 100X)
• Total magnification is calculated by multiplying the magnifying power of the ocular lens by the magnifying power of the objective lens being used
• Total magnification examples: x10 ocular x x4 objective = x40, x10 ocular x x10 objective = x100, x10 ocular x x40 objective = x400, x10 ocular x x100 objective = x1,000
• Photomicrograph is photographs taken through the lens system of the compound light microscope
• Types of microscopes: Light Microscopes, Two-Photon Microscopes, Super Resolution Light Microscopes, Scanning Acoustic Microscopes, Electron Microscopes, Scanned Probe Microscopes
• Types of light microscopes: Compound light microscope, Darkfield microscope, Phase contrast microscope, Differential interference microscope, Fluorescence microscope, Confocal microscope
• Compound light microscope is the simplest and most common type of light microscope, utilizes transmitted light coming from a condenser and uses attenuation to contrast between acid and basic dyes
• Darkfield microscope uses a darkfield condenser with an opaque disc to block light reflected directly through the objective lens, allowing only light that is refracted or scattered by the specimen to reach the objective
• Light Microscopes are any type of microscope that utilizes visible light
• Brightfield microscopes are also coined as light microscopes