microbio 3

micrometer (µm)

one millionth of a meter, 10

nanometer (nm)

one billionth of a meter, 10

resolution

the distance between two objects where the they can be seen as separate

contrast

the difference in light absorbance between two areas

brightfield microscope

simplest light microscope

condenser

light passes through, converging the light beams into a focused area

diaphragm

controls the amount of light that passes through the sample and lens

objective lens

the lens closest to the sample and has the greatest magnification

ocular lens

the eyepiece, or the lens the person looks through

samples are usually fixed to the slide, most commonly by heat, but can also be from chemicals

phase contrast microscope

able to visualize some structures that are often invisible with special condensers and objectives

dark field microscope

greatly increases the contrast of a specimen and background, reflects light off of the specimen at an angle

fluorescence microscope

similar to dark field but uses UV dyes and lights to visualize differing parts or together

Confocal (laser scanning) microscopes

like fluorescence but in 3D, uses lasers for a single plane and pieces them together

electron microscope

uses electrons with shorter wavelengths rather than light to increase resolution down to 1 nm, requires a fixed sample

transmission electron microscope

uses a heavily treated thin slice of a sample, placed between the electron beam source and the detector for a 2D image as the electrons pass through the sample

scanning electron microscope

uses a heavily treated, gold/palladium coated, thin slice of a sample, between an electron source and detectors for a 3D image as the electrons bounce off of the sample

Scanning transmission electron holography microscopes

similar to TEM and SEM, but with a holography technique to study surfaces of proteins and subcellular structures, can zoom to 35 pm (a trillionth of a meter, 10

gram staining

different bacteria react differently to various dyes

gram positive

thick cell wall with many overlapping strands of peptidoglycan, traps the crystal violet and iodine in the cell wall, staining it purple

gram negative

relatively thin peptidoglycan layer and an outer membrane of lipopolysaccharides, dye washes away with an alcohol wash, recolored with safranin

differential stain

a staining technique to separate specimens into further subgroups

wet mount

a small drop of a sample is placed on a slide and covered with a glass coverslip, live sample, can be used to observe motility

simple staining

uses a solution of a positively charged dye to bind and stain the negatively charged membrane of the sample to observe size, shape, and arrangement of cells

negative staining

using a negatively charges stain to repel from the membrane and have a contrast between the now dark background and the sample

acid fast staining

used for cells with a high resistance to staining, red dye is used to color cells with a thick lipid

giemsa

combines with wright’s stain as a combination stain for blood samples to determine presence of bacteria, human is purple, bacteria is pink