Question

1.if you were asked to set up an Ames test for your chemical company, would you use Salmonella Strain A or Strain B? Briefly explain your reasoning

2.how can you be certain the substance from home was not contaminated with protorophic bacteria? my substance was hair gel

i just need to understand the concept

Answer 1

Answer of question 1:

To understand the carcinogenicity of mutants or chemical, Bruce Ames developed “Ames test” in 1970. In the Ames test, a mutational reversion assay employing several special strains of Salmonella enterica serovar Typhimurium, each of which a different mutation has in the histidine biosynthesis operon; usually called as histidine auxotrophs. The bacteria also have mutational alterations of their cell walls that make them more permeable to test substances. Different strains of auxotrophic Salmonella bacteria is developed through transformation of different kinds of plasmid (e.g. pKM101) for their improvement in sensitivity.

In the Ames test, tester strains of auxotrophic Salmonella enterica serovar Typhimurium are plated with the substance being tested and the appearance of visible colonies followed after incubation at 37 °C. To ensure that DNA replication can take place in the presence of the potential mutagen, the bacteria and test substance are mixed in dilute molten top agar to which a trace of histidine has been added. This molten mix is then poured on top of minimal agar plates and incubated for 2 to 3 days at 37°C. All of the histidine auxotrophs grow for the first few hours in the presence of the test compound until the histidine is depleted. Once the histidine supply is exhausted, only revertants that have mutationally regained the ability to synthesize histidine continue to grow and produce visible colonies. These colonies need only be counted and compared to controls in order to estimate the relative mutagenicity of the compound: the more colonies, the greater the mutagenicity.

For the selection of different types of Salmonella, it’s a hit and trial method to optimized the better response to particular compound,

Conclusion: Hence, through this Ames test, we can determined the carcinogenicity of any molecules.

Answer of question 2:

Unlike auxotrophic bacteria, prototrophic bacteria have the ability to synthesize all the compounds needed for growth. Hence, this prototrophic bacteria can grow on any nutrient media like nutrient agar media, LB media, etc.

To test our object (e.g. Hair gel in question) for the presence or absence or prototrophic bacteria, a swab from the substance taken and spread or streaked on any nutrient agar plates or also dissolved into any nutrient broth (both media must be sterilized at 15psi, 121 degree Celsius) and incubate at 37 °C in the BOD incubator, after 24 to 48 hrs, we can observed any growth on/ in the media plates or broth. If any colonies are present then we conclude for the presence of prototrophic bacteria otherwise free from the prototrophic bacteria.

Conclusion

Prototrophic bacteria can grow on any nutrient rich media.