Cytotoxicity

Cytotoxicity is the quality of being toxic to cells. Cells exposed to a cytotoxic compound can respond in a number of ways. The cells may undergo necrosis, in which they lose membrane integrity and die rapidly as a result of cell lysis; they can stop growing and dividing; or they can activate a genetic program of controlled cell death, termed apoptosis.

Cytotoxicity testing: measuring viable cells, dead cells, and detecting mechanism of cell death.

Testing the effects of compounds on the viability of cells grown in culture is widely used as a predictor of potential toxic effects in whole animals. Among the several alternative assays available, measuring the levels of ATP is the most sensitive, reliable, and convenient method for monitoring active cell metabolism. However, recently developed combinations of methods have made it possible to collect more information from in vitro cytotoxicity assays using standard fluorescence and luminescence plate readers. This chapter describes two assay methods. The first utilizes beetle luciferase for measuring the levels of ATP as a marker of viable cells. The second more recently developed multiplex method relies on selective measurement of three different protease activities as markers for viable, necrotic, and apoptotic cells. Data analysis from the measurement of three marker protease activities from the same sample provides a useful tool to help uncover the mechanism of cell death and can serve as an internal control to help identify assay artifacts.

Bacteria

Bacteria

Bacteria constitute a largedomain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste,  and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. They are also known to have flourished in manned spacecraft.

Types Of Bacteria

Comma-shaped Bacteria
(Vibrio Cholera)

Flagellated Bacteria
(Tetanus Bacteria)

Rod-shaped Bacteria
(Salmonella)

Spherical-shaped Bacteria
(Streptococcus)

Spiral-shaped Bacteria
(Treponema Pallidum)

Bacteria Based On Cell Wall Contents

Gram-positive bacteria retain the color of the crystal violet stain in the Gram stain. This is characteristic of bacteria that have a cell wall composed of a thick layer of a particular substance (called peptidologlycan). The Gram-positive bacteria include staphylococci ("staph"), streptococci ("strep"), pneumococci, and the bacterium responsible for diphtheria(Cornynebacterium diphtheriae) and anthrax (Bacillus anthracis). The thick layer of Peptidoglycans is stained purple by the crystal violet dye, which is why gram-positive bacteria appear purple or blue.

Gram-negative bacteria lose the crystal violet stain (and take the color of the red counterstain) in Gram's method of staining. This is characteristic of bacteria that have a cell wall composed of a thin layer of a particular substance (called peptidoglycan). The Gram-negative bacteria include most of the bacteria normally found in the gastrointestinal tract that can be responsible for disease as well as gonococci (venereal disease) and meningococci (bacterial meningitis). The organisms responsible for cholera and bubonic plague are Gram-negative. The thin layer of Peptidoglycans cannot retain the crystal violet dye, and thus appear red or pink due to the retention of the counter-stain.

What I Learned

• I Learned the two types of bacteria based on the cell wall contents
• I Learned the five types of bacteria based on their shapes.

What I Did

• I searched information about bacteria using the internet.

I Can Apply My Learning To

• I can apply my learning to the research proposals that i will make.