Bacterial Cell Viability

Agar plate with bacteria

Bacterial cell viability tests are used to determine if a sample of cells is alive. Tests can determine if a sample is alive even when the cells are not producing. The testing methods range from simple staining and testing of reproduction ability to more advanced techniques. Cell viability tests are especially useful in determining a bacterial strain's unique physiology. These tests include exposing a bacterium to a wide range of environmental conditions.

CeCell Division

Count the CFUs.

Cell viability can be determined simply by the ability of the bacteria to reproduce.This is determined by growing bacteria on an agar plate and then placing the plate under a microscope. While looking under the microscope you must count how many Colony Formation Units are present. By using this test you can compare the cell viability of different strains by comparing the numbers of CFUs. The more CFUs you have, the higher the cell viability.

Gram Stain

Gram stain under the microscope

Gram stains allow you to visualize the presence of bacteria in a sample because the cells will dye purple. This test is most commonly performed using a glass microscope slide with a small sample of bacteria placed on it. The bacterial sample is briefly heated so it will attach and is then dyed with crystal violet solution. The sample is dyed after ample incubation time for a bacterial culture has been provided. After dying, the sample is washed and placed under a microscope and viewed. All cells that have grown will be dyed purple.

TestSpecific Gene Transcripts

DNA Helix

When an organism is alive it must use transcription in order to retrieve information from its DNA. After the information is transcribed into messenger RNA, it can be used in a process called translation to produce amino acids. These amino acids are then configured into the proteins that allow for the survival of an organism. By testing for the transcription of specific genes, it is possible to see if the bacteria is alive or not. This can be detected using polymerase chain reaction (PCR) methods or microarrays.

Stability of Ribosomal RNA

When any living organism dies, its RNA and DNA begin to degrade. The reason for testing ribosomal RNA instead of regular RNA is that there is much more ribosomal genetic material in any organism than regular RNA. Since it is present in such a large quantity it does not require PCR amplification as regular RNA would. Cell viability would correlate with intact RNA.

Permeability of the Cell Membrane

A cell must actively exchange materials through its cell membrane in order to meet its energy, water and nutrition needs. If a cell is not alive, it cannot command its cell membrane to get rid of wastes and absorb necessary supplements for survival. By exposing a cell membrane to fluorescent compounds, a sample can be tested for permeability. This permeability is then measured by the level of fluorescence under a UV light. Higher levels of fluorescence correspond with higher levels of permeability. This allows for the measurement of cell viability through fluorescence.

References

• EMBO Reports: A Matter of Bacterial Life and Death
• Biochemica: Cell Proliferation and Viability Measurement
• HighBeam Research:Transcriptional Activity Around Bacterial Cell Death Reveals Molecular Biomarkers for Cell Viability