5.15: Chapter Summary

Aseptic technique reduces the chance of introducing unwanted microorganisms during handling. Sterile supplies can become contaminated if protected surfaces touch a glove, work surface, or used item. Organized cabinet work and suitable airflow support careful transfers. Cleaning removes material. Disinfection reduces or inactivates microbes using suitable treatment and contact time. Sterilization eliminates viable microorganisms through a validated process. These actions have different purposes. Mycoplasma are very small bacteria without cell walls. They can affect cell behavior without making the medium cloudy. A pure culture lets the intended population be studied without unwanted organisms or another cell line changing the result. Purity does not mean that every cell is genetically identical. Microbial testing and cell identity checks answer different questions. Interpret tests only when their required controls pass. Report handling errors, restrict affected work, and preserve records for the investigation.

Key Terms

Aseptic technique	contamination	microbial contamination	cross-contamination
chemical contamination	endotoxin	critical surface	cleaning
disinfection	sterilization	decontamination	contact time
turbidity	yeast	mold	hypha
mycoplasma	PCR	LAMP	cell line authentication
STR profiling	quarantine	positive control	negative control
interference control	limit of detection	sterility	antibiotic
deviation	corrective action	preventive action	incident
pure culture
microorganism

Review Questions

1. Why can a clear culture still be contaminated?

2. Give an example of a critical surface and explain why it must be protected.

3. Distinguish cleaning, disinfection, and sterilization.

4. Explain why wiping a bottle exterior does not establish the sterility of its contents.

5. What does disinfectant contact time require?

6. Why is an alcohol wipe not evidence of sterilization?

7. How can a shared reagent connect contamination events in several cultures?

8. Explain why correct cabinet airflow cannot prevent contamination from a touched pipette tip.

9. Which observations might suggest bacterial, yeast, or mold contamination?

10. Why are appearance and routine light microscopy insufficient to exclude mycoplasma?

11. Distinguish cell authentication from microbial contamination testing.

12. What can a valid negative contamination test establish, and what remains uncertain?

13. Why must a result be withheld when a required control fails?

14. Explain why antibiotics cannot replace aseptic technique.

15. What details should be recorded after a handling error?

16. What is a pure culture, and why is culture purity important? Explain how unwanted microbes or cells from another line could affect a mammalian cell culture experiment.

Apply Your Understanding

A technician touches a sterile pipette tip to a glove, then uses it to transfer medium into a culture. The culture remains clear. Several days later, an agar screen shows no growth, but a mycoplasma test gives an unclear color result. The positive control does not show its expected response.

Identify the handling error and explain what the clear medium and negative agar screen can establish. Explain why the mycoplasma result is not ready for interpretation. Describe the records, restrictions, and follow-up evidence needed before the culture's suitability can be decided.

In the handling-error case above, identify the contact that broke aseptic technique. Explain why clear medium does not show that the transfer was acceptable.

The mycoplasma positive control fails. Decide whether the sample can be called negative and explain what must happen before interpretation.

Three cultures sharing one medium bottle develop similar problems. Draw a proposed route of contamination and identify records that could test it.

A fibroblast culture contains cells from a different human cell line but no detected microbes. Explain how the mixed population could affect a growth experiment and identify the type of check needed.