John Hay
John Hay Biomedical
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Principles of Biomedical Technology (Principles of Biomedical Science)
Unit 3: Unit 3.1 Nosocomial NightmarePBS 3.1Handling, Preparation, Storage and Disposal

Label cultures and slides

Base not lid, before not after, and four things on every label. Learn what makes a label still useful three days later to someone who was not there.

Builds on (2 levels back)curriculum · high confidence
  • A lid does not stay with its plate: Lids come off during streaking and go back on afterwards, and nothing guarantees each one returns to the plate it started on.
  • You will not remember which was which: Three plates of the same medium streaked in the same period are indistinguishable by sight within minutes.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Now handle labels on slides and tubes, and what to do when one goes missing.

Step 1: A slide gets its mark on the frosted end
The frosted strip takes pencil or marker and sits away from the smear, so nothing is written over the area you will be looking at down the microscope.
Step 2: Marks have to survive the process
A stain run involves alcohol and rinsing, so a label written in something that dissolves will be gone by the time you need it. Match the marking to what the item is about to go through.
Step 3: An unidentified item is not renamed by guessing
If a plate or a slide loses its identity, it does not become the one you think it is. It is set aside and the observation is repeated, because a confidently wrong identity spreads into every conclusion after it.
Practice

Where on a microscope slide should the identifying mark go, and why there?

Reviewed
  1. A.In the middle, next to the smear, so the two stay together
  2. B.On the slide box rather than the slide, to keep the glass clean
  3. C.On the frosted end, which takes a mark and sits clear of the smear
  4. D.On the underside beneath the smear, so it cannot rub off
Show the worked solution ▾

Answer: C. On the frosted end, which takes a mark and sits clear of the smear

  1. Step 1: Ask what has to stay clear: The smear is what you will view, so nothing can be written over or under it.
  2. Step 2: Find the part designed for writing: The frosted strip takes a mark and is away from the viewing area.

Why it's right: The frosted strip exists to be written on and sits clear of the area you view. A mark anywhere on or under the smear ends up in the field of view.

Why the others miss:
  • A: A mark beside the smear can be dragged into it during staining and rinsing, and it crowds the area you need to scan.
  • B: A box holds several slides, so a label on it identifies the set rather than any individual slide in it.
  • D: A mark underneath the smear is directly in the light path and shows up in the field of view.

Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9

One of three plates comes out of storage with its label rubbed away. A student is fairly sure it is the third sample. What should happen?

Reviewed
  1. A.Relabel it as sample three, since the other two are still readable
  2. B.Record it as sample three and note that the label was damaged
  3. C.Compare its growth against the other two and assign it by elimination
  4. D.Set it aside as unidentified and repeat the streak from the stored sample
Show the worked solution ▾

Answer: D. Set it aside as unidentified and repeat the streak from the stored sample

  1. Step 1: Ask what evidence remains: None on the plate itself. What is left is a recollection.
  2. Step 2: Ask what a wrong assignment would do: It attaches a real result to the wrong patient sample, and every conclusion drawn afterwards inherits that error.

Why it's right: Nothing on the plate ties it to a sample any more, so any identity assigned to it is a recollection. Repeating the streak from the stored sample costs one period; a wrong assignment travels into every conclusion after it.

Why the others miss:
  • A: Relabelling replaces missing evidence with a guess and makes the plate look properly identified to everyone who sees it afterwards.
  • B: The note documents the uncertainty honestly and then the result is used anyway, which is the part that causes the harm.
  • C: Elimination assumes the other two are correctly identified and that this plate must be the remaining one, and neither is established.

Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9

Where you'd see this
  • A student marks slide frosted ends before making smears in Activity 3.1.6, rather than trying to keep track of an order.
Careers that use this
Histotechnician: Marks every slide before processing, because slides go through solvents that would remove anything written in the wrong medium.
Guided notes

Fill these in as you work through the lesson.

Big idea: A label is written for a stranger reading it later, not for you two minutes from now. It goes on the part that never gets separated, and it goes on before the work starts.
Key terms: write the meaning
  • Base (the half of the plate holding the agar):  
  • Permanent marker (will not wash off in the incubator):  
  • Initials (who to ask if it is unclear):  
  • Medium (what the organism is growing on):  
The rule

Label the   of a plate, not the lid, and write it   you begin streaking, not afterwards.

Check yourself
  1. Give the reason a lid is the wrong place for a label. 
  2. List four things a useful plate label carries. 
  3. Explain where on the base to write so the colonies are still visible. 
Work one example

Three plates go out for three patient samples. Before anything is streaked, each base gets the sample identifier, the date, your initials and the medium, written around the outer edge in permanent marker. Whichever lid ends up on whichever plate, every plate still says what it is.