Where contamination comes from
By the end of this lesson
- Identify external and internal contamination pathways
- Explain why clear cultures can still carry risk
- Investigate repeated patterns using source and workflow history
See it
Microbial contamination can originate on or inside source plants, from the laboratory environment, tools, vessels, water, media components, operators, or cross-contamination between cultures. Endophytic organisms can be especially difficult because they may be inside plant tissues.
Understand it
Identify external and internal contamination pathways
The source plant is part of the contamination system.
Contamination can originate externally or internally in source material as well as through the lab workflow.
Explain why clear cultures can still carry risk
Repeated contamination patterns can reveal a process or source problem.
Some contamination is latent or difficult to detect, so a clear appearance is an observation rather than proof of absence.
Investigate repeated patterns using source and workflow history
Latent contamination may not be obvious immediately.
Shared source and workflow links help investigate patterns without prematurely assigning one cause.
Worked example
Two jars look clear on the first check but later develop similar changes. They share a donor plant and a transfer session. Record both links: a source-associated problem and a handling pathway remain possibilities, rather than assuming the first clear appearance proved absence of contamination.
Explain your decision before opening the worked reasoning below.
Show the worked reasoning
There are multiple potential entry pathways, so investigation should not exclude sources merely because one looks obvious.
Pattern comparison can narrow hypotheses, but appearance or a shared donor alone does not prove the exact cause.
A clear vessel today does not prove that the culture is contamination-free.
Try it
Which links should be retained in the example?
Use the worked example above to explain your answer in your own words before taking the quiz.
Lesson quiz
Assessment version: 2026-10-15-v2. Previous reading-completion markers are retained. This revised quiz has its own result.
Apply it
Use the worked example to write a short decision record: what did you observe, which rule did you apply, and what would you check before acting?
Completion marks reading progress, not a quiz pass or professional certification.