Differential staining - bacterial outer cell structure, bacterial intracellular components, differential stains

differential stains are used to

observe bacterial morphology and divide bacterial cells into distinct groups

the most widely used clinical application of differential staining is

the gram stain

for identification of unknown bacteria, differential staining can be

combined with other techniques, such as differential and/or selective media or biochemical tests

the bacterial envelope consists of

plasma membrane surrounded by a cell wall

the plasma membrane consists of

a phospholipid layer with several embedded proteins facilitating cell signaling and transport

the main function of the plasma membrane is to

protect the cell from the extracellular environment

provide shape of the bacteria

two main types of bacterial walls - differentiated by gram-staining characteristics

gram-positive and gram-negative cell wall

gram-positive cell wall

layer of thick peptidoglyan

gram-negative cell wall

thin peptidoglycan layer and an outer membrane

some bacteria contain a capsule that

surrounds the cell wall

can help cells adhere to surfaces

capsules are

relatively impermeable

made of polysaccharides and sometimes proteins

considered a virulence factor - protects bacteria from phagocytosis by macrophages and against desiccation

some bacteria contain extracellular features such as

fimbriae, pili, and flagella

for movement, attachment, and transferring genetic content

bacteria contain several components in the

cytoplasm which is surrounded by the plasma membrane

bacterial DNA is located

freely in the cytoplasm in the area called the nucleoid

bacterial DNA shape and non-coding regions

circular and contains very few non-coding regions compared to eukaryotic DNA

the DNA content of the nucleoid

varied between bacterial strains and can be adapted to the environment the bacteria live in

DNA is transcribed

freely in the cytoplasm

DNA is translated into proteins by

70S ribosomes

the 70s bacterial ribosome consists of

a small 30S subunit and a larger 50S subunit

some bacteria also contain plasmids which are

extracellular circular DNA molecules

plasmids usually hold

genetic materials that can give bacteria a survival advantage in the environment they reside in

Bacteria can live in environments that are

low on nutrients

to accommodate external fluctuating nutrient levels, bacteria can

store nutrients in inclusion bodies in the cytoplasm

these can be highly variable and can contain carbohydrates, lipids, proteins, or inorganic compounds

Gram stain

• most widely used

• based on differenced in structure of the bacterial cell wall

• gram positive vs gram negative

• typically the first step in the identification of unknown bacteria

gram positive cells

• thick peptidoglycan layer

• polymer made of amino acids and sugars in the cell wall

• crystal violet binds to peptidoglycan, rendering the cell purple

gram-negative cells

• thinner peptidoglycan layer

• crystal violet staining is washed out when the cells are exposed to ethanol

• stains pink by counterstain (safranin/fuchsine)

peptidoglycan is the target of a class of antibiotics called

B-lactam antibiotics

gram-negative bacteria are less susceptible to B-lactam antibiotics because

they have an outer membrane

Acid fast stain procedure

• carbol fuchsin stain the cell wall red

• non-acid-fast bacteria lose the red color and are counterstained BLUE with methylene blue

Acid-fast stain

• used on Mycobacteria

• contain mycolic acid in their walls which makes them resistant to decolorization

• not as commonly used as the gram stain

endospores are

dormant structures

endospores are produced by

some bacteria when conditions are unfavorable

Endospores can survive without

nutrients and are very resistant to extreme temperatures, radiation, and chemical disinfectant

why are endospores difficult to stain

due to their tough, impermeable exterior

endospore staining uses

heat to allow the dye malachite green to penetrate the spores

any bacterial cells are decolorized and counterstained with safranin

Gram positive vs gram negative

purple vs pink

non acid fast vs acid fast

blue vs red

bacteria with spores vs bacteria without spores

green vs pink