MCBL Lecture 6

What is an Ames Test?

Examines ability of a chemical substance to cause mutations or strength of the chemical substance.

How do mutations work?

Mutagen (Chemical) causes mutations (change in nucleotide) causes to become a mutant.

Spontaneous Mutations

DNA replication errors

Induced Mutations

Chemical, physical, biological agents.

Point mutations

Classed based on base pair changes.

• Point mutation: Change in a single base

• Transition/Transversion/Insertion or Deletion.

• Missense: changes the amino acid sequence to another

• Nonsense: change amino acid to premature stop codon

• Silent: No change in amino acid.

Framshift Mutations

Changes the open-reading frame of the gene. Genetic code based on three-bases.

What does streptomycin do?

Irreversibly binds to 16s rRNA & S12 protein of the bacterial ribosome. Inteferes with translation.

What are Ames Test Controls?

No growth on streptomycin: something not mutagenic should not induce streptomycin resistance mutations.

Cells were not killed by the mutagen

There are no contaminating microbes in the test substance.

What are the 4 principles of clincal microbiolgy?

Identification of a potential pathogen/bacterium is critical

Track spread of disease

Anticipate likely sequelae

Using appropriate treatments

Ways to collect specimen?

Blood, pus, urine, sputum, throat, stool, cerebrospinal fluid

Ways to identify pathogen?

• Using microbial physiology

• Structure

• Determination of growth on selective or differential media

• Using profile API index strip technology (biochemical tests strips each rxn of color change)