Question

If I performed a transformation, how do I prevent growth that have not been transformed?

if i wants to perform cell culture, what should i do to avoid contamination?

Answer 1

Possible cause	Recommendation
Antibiotic-resistant strain	Check the genotype of the host strain for antibiotic resistance. Include a negative control without DNA in the transformation step for verification of antibiotic effectiveness. Assuming the correct genotype, untransformed cells should not survive the antibiotic selection.
Vector plasmid recombined into the host chromosome	The vector plasmid may have integrated into the bacterial chromosome, conferring antibiotic resistance. When this occurs, colonies may appear to lack the transforming DNA, since independently replicating plasmids cannot be detected by the usual screening methods (which selectively purify or detect the plasmids and not the chromosomal DNA). Use competent cells with the recA mutation to prevent recombination and allow stable propagation of the transforming plasmid vector.
Satellite colonies	Limit the incubation time to <16 hours after plating to avoid antibiotic breakdown around overgrown colonies, which can lead to formation of satellite colonies. For screening, pick well-isolated colonies with no visible satellite colonies. For selection of ampicillin-resistant colonies, consider using the more stable semisynthetic antibiotic carbenicillin.
High number of cells plated	Adjust the cell volume and/or dilutions as necessary during plating to reduce and optimize the number of colonies formed. Over-plating of cells could result in degradation of plate antibiotics and growth of cells without transforming DNA.
Cell contamination	Use sterile tools and labware, media, and reagents where appropriate or required in the workflow. Make sure spreading rods and/or glass beads are sterile, and cell plating is performed under aseptic conditions.

2) some essential tips to maintain an aseptic environment and prevent cell culture contamination.

1. Wear gloves, lab-coats and use hoods
2. Use your hood correctly
3. Clean your incubator and water bath regularly.
4. Spray EVERYTHING with ethanol
5. Minimize exposure of cells to non-sterile environments.