Disk diffusion and MIC lab
Safety gate · before any work
- Goggles and gloves on before opening any bacterial culture material; keep on until cleanup is complete.
- Treat all bacterial materials as biohazardous: no contact with skin, eyes, or mouth.
- Open plate lids only briefly and only near the workspace; do not talk, sneeze, or cough over an open plate.
Do now
Run a disk-diffusion test and connect zone of inhibition to minimum inhibitory concentration.
- Hand in
- Disk-diffusion data table: antibiotic name, zone of inhibition measurement (mm), and effectiveness ranking; plus one sentence connecting zone size to MIC.
- Where
- Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
You get two school days for every day you were absent, so this deadline moves with you.
You place four disks on one bacterial lawn and get clear rings of different sizes. How do you turn those millimeter measurements into a ranking of which drug works best?
Run a disk-diffusion test and connect to minimum inhibitory concentration.
- • You will be able to set up a disk-diffusion test safely.
- • You will be able to measure a .
- • You will be able to relate zone size to MIC and effectiveness.
- If a bacterium keeps growing right up to the edge of an disk, was that drug strong or weak against it?
- Why do we put on goggles and gloves before handling a plate of growing bacteria?
- 1Put on goggles and gloves and confirm your plate is labeled with each disk.
- 2Place disks on the bacterial lawn using .
- 3Set the plate to incubate and write what a clear zone around a disk will mean.
- 4Once zones form, measure each in millimeters.
- 5Rank the antibiotics by zone size and relate larger zones to greater effectiveness.
- 6Define MIC and explain how a larger zone hints at a lower MIC.
What did this day actually feel like?
Disk diffusion and MIC lab
LAB Disks of antibiotic on a lawn of bacteria, and you measure the clear zone where nothing grew. For any one antibiotic a bigger zone means this organism is more susceptible to it. You cannot rank two different antibiotics by comparing zones, because each molecule spreads through agar at its own rate, so every zone is read against that drug's own breakpoint table. Getting an actual minimum inhibitory concentration takes a dilution series, not a disk.
Measuring the zone is harder than it sounds because the edge is not always sharp. Two of us measured the same plate and got different numbers, so we agreed on a rule and remeasured everything.
AT HOME, THE NIGHT BEFORE TUE SEP 29 Resistance and stewardship How resistance arises and spreads. It is not that individual bacteria learn, it is that the ones that already survive get to reproduce.
Selection pressure is why the length of a course matters. The old line was that stopping early breeds resistance.
For most common infections the evidence points the other way: the longer any antibiotic is in you, the longer it selects resistant bacteria in your own normal flora. Take the course you were actually prescribed, and do not assume longer is safer.
Turned in: notebook → Lab Notebooks folder
Fiction. There is no such student. The lessons, labs and dates are the real planned course; the student, the classmates and the conversations are invented.
The same day, drawn.
Disks of antibiotic on a lawn of bacteria, and you measure the clear zone where nothing grew. For any one antibiotic a bigger zone means this organism is more susceptible to it.
ME
We measured the same plate and got different numbers. Agree on a rule, then remeasure everything.
Fiction. There is no such student. The lessons, labs and dates are the real planned course; the student, the classmates and the conversations are invented.
🛠 Get unstuck · pick your level
Lab day: Tier 1 is the whole class at the bench. No extension today.
🔑 Today's words · 5
Tap a word in the lesson for a plain meaning and one example. Recycled into next week's Do-Now.
Do the work · 80-minute blockfirst 5 min = hook▸
💡 Big idea: Because an effective can stop bacteria even where it has diffused to a low concentration, a wider clear zone signals a lower minimum inhibitory concentration and a stronger drug.
- 0-8 minDon goggles and gloves; confirm plate is labeled with the abbreviation for each disk location
- 8-22 minUsing , place disks on the bacterial lawn at the labeled positions
- 22-30 minSet plate to incubate (inverted); write in notebook what a clear zone will indicate
- 30-50 minAfter (or using pre-incubated plates): measure each in millimeters with a ruler
- 50-65 minRank antibiotics by zone size from largest to smallest; record in a
- 65-80 minDefine MIC in notebook; write one sentence connecting larger zone to lower MIC and greater effectiveness
- • The test has been the clinical standard for sensitivity testing since 1966 and is still used in hospitals today.
- • The data you collect today will drive your resistance and stewardship analysis on Thursday and your report on Friday.
- • is critical: will produce zones that mean nothing.
- • Exit goal: a of zone measurements in millimeters for each disk, with an effectiveness ranking.
- • The test measures effectiveness by placing antibiotic-impregnated disks on a bacterial lawn and measuring the clear zone that forms.
- • The is the area around the disk where bacteria could not grow; a larger zone indicates the diffused farther and was effective at lower concentrations.
- • The minimum inhibitory concentration (MIC) is the lowest concentration of an that prevents visible bacterial growth; a larger zone correlates with a lower MIC.
Bacterial structure, antibiotic mechanisms, MIC, resistance, and stewardship. · and MIC lab
Day 3 of this lesson. Open this exact section in myPLTW (find it in Clever, Microsoft sign-in), then do the work below.
Do this: Open Activity 1.2.2 Which Is the Best Choice in myPLTW and apply your mechanism knowledge to the case patient.
Complete the -selection decision guide and write your best-choice justification.
Mechanism chart should be done (Tuesday); selection and justification due today.
Best-choice justification with mechanism reasoning in notebook.
The official PLTW activity stays inside myPLTW. If myPLTW will not open, use F1 and E1-E3 on this page to complete today's local evidence decision, then make up the official activity when access returns. Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
Check things off as you work, then submit. This tells Mr. Mendoza how you're doing so he can help the class. It does not replace turning in your producible through the submission route shown below.
Use the code Mr. Mendoza gave you, not your name. Saved on this device.
Bacterial structure, antibiotic mechanisms, MIC, resistance, and stewardship. · Disk diffusion and MIC lab
Open Activity 1.2.2 Which Is the Best Choice in myPLTW and apply your mechanism knowledge to the case patient.
Mechanism chart should be done (Tuesday); selection and justification due today.
This is how Mr. Mendoza sees the class keeping pace with PLTW. Be honest, it only helps if it is accurate.
🎯 Run a disk-diffusion test and connect to minimum inhibitory concentration.
- Put on goggles and gloves and confirm your plate is labeled with each disk.
- Place disks on the bacterial lawn using .
- Set the plate to incubate and write what a clear zone around a disk will mean.
- Once zones form, measure each in millimeters.
- Rank the antibiotics by zone size and relate larger zones to greater effectiveness.
- Define MIC and explain how a larger zone hints at a lower MIC.
Data table: Disk-diffusion : name, measurement (mm), and effectiveness ranking; plus one sentence connecting zone size to MIC.
Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not. Use the checklist just below and upload by 11:29 PM for full credit. Absent with an excused absence? You get two school days for every day you were absent, so this deadline moves with you.
| Task | Who |
|---|---|
| Put on goggles and gloves and confirm your plate is labeled with each disk. | _______ |
| Place disks on the bacterial lawn using . | _______ |
| Set the plate to incubate and write what a clear zone around a disk will mean. | _______ |
| Once zones form, measure each in millimeters. | _______ |
| Rank the antibiotics by zone size and relate larger zones to greater effectiveness. | _______ |
| Define MIC and explain how a larger zone hints at a lower MIC. | _______ |
Working solo? Put your own name in "Who" for every row.
- You will be able to set up a disk-diffusion test safely.
- You will be able to measure a .
- You will be able to relate zone size to MIC and effectiveness.
- 1Do thisRun a disk-diffusion test and connect zone of inhibition to minimum inhibitory concentration.
- 2Use this resource
- 3Submit thisData table: Disk-diffusion data table: antibiotic name, zone of inhibition measurement (mm), and effectiveness ranking; plus one sentence connecting zone size to MIC.
- 4Submit it here
- 1Open the drop folder.
- 2Sign in with your district Microsoft account, not a personal one.
- 3Upload the file, named Lastname_Firstname__Assignment Title.
- 4Your own upload panel says Uploaded with a green check: that is your receipt.
Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not. Genetics of Disease (Medical Interventions) › Bacterial structure, antibiotic mechanisms, MIC, resistance, and stewardship. › Data tableOpen the drop folder
Learn it · deck, reading, and vocabulary▸
The deck carries the prior idea forward, lets you inspect an analogy, maps the rule to biology, and ends with the same evidence decision and exit ticket used on this page.
Generated from this lesson's canonical data with a red-team citation check.
Because an loses power each time it is used, appropriate use is a shared responsibility so that the drug still works when someone truly needs it.
Because an effective can stop bacteria even where it has diffused to a low concentration, a wider clear zone signals a lower minimum inhibitory concentration and a stronger drug.
A smoke alarm detects signs of fire but can also react to burnt toast.
- What does the alarm detect?
- What creates a false alarm?
- What evidence is needed before declaring a fire?
A screening signal changes what to investigate next; it does not automatically prove the cause.
Biomedical tests have measured performance and biological sampling limits that a household alarm does not capture.
- • Alarm signal maps to a test result.
- • Burnt toast maps to a .
- • Inspection maps to confirmation or the next test.
Driving question: You place four disks on one bacterial lawn and get clear rings of different sizes. How do you turn those millimeter measurements into a ranking of which drug works best?
What you already know: Because an loses power each time it is used, appropriate use is a shared responsibility so that the drug still works when someone truly needs it.
New idea: Because an effective can stop bacteria even where it has diffused to a low concentration, a wider clear zone signals a lower minimum inhibitory concentration and a stronger drug.
Visual or model: F1. F1. A lesson illustration or teaching diagram for Disk diffusion and MIC lab. Use it with E1-E3; it is a model or context image, not experimental or patient data. What to notice: Trace the labeled testing, treatment, or biological process and identify where evidence limits the decision.
- Observe or measure the relevant feature in and MIC lab.
- Organize the observation with a stable evidence ID.
- Apply this rule: A screening signal changes what to investigate next; it does not automatically prove the cause.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: You place four disks on one bacterial lawn and get clear rings of different sizes. How do you turn those millimeter measurements into a ranking of which drug works best?
What the evidence supports: E1-E3 and F1 support the daily take-home when the response meets the stated success criteria.
What it cannot prove: The package does not support claims beyond this lesson's or any real patient diagnosis.
- • : A medicine that kills bacteria or stops them from multiplying, used to treat bacterial infections but useless against viruses like the common cold.
- • : Describing an agent that stops bacteria from growing and multiplying without directly killing them, so the immune system can then clear the infection.
- • : Describes an agent that kills bacteria outright, rather than only stopping them from multiplying.
- • MIC: Minimum inhibitory concentration, the lowest concentration of an that stops visible growth of a microbe, used to gauge how effective the drug is.
- • : The clear ring around an disk on a bacterial plate where growth is blocked, with a larger ring meaning the drug is more effective.
- • resistance: The ability of microbes to survive drugs that once killed them, often after genetic changes let them evade the medicine.
- • : A small circular piece of DNA found in bacteria that copies itself separately from the main and is often used to carry genes in the lab.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
The test measures effectiveness by placing antibiotic-impregnated disks on a bacterial lawn and measuring the clear zone that forms.
Limit: E1 supplies context or an observation; it does not by itself establish the explanation.
Because an effective can stop bacteria even where it has diffused to a low concentration, a wider clear zone signals a lower minimum inhibitory concentration and a stronger drug.
Limit: E2 is a teaching statement or comparison and must be checked against the task evidence.
You will be able to set up a disk-diffusion test safely.
Limit: E3 supports only the result or product criterion named here; it cannot justify a broader clinical or causal claim.
PLTW-GEND-2026-09-28 · Simulated classroom evidence scenario
Your role: medical interventions team member
Decision: Your team must decide what the evidence from and MIC lab supports before submitting the labeled and result claim named on the lesson page.
- • Choose the strongest supported explanation.
- • Choose the next evidence to collect.
- • Hold the decision because the evidence is insufficient.
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Submit it as the labeled and result claim.
Claim ceiling: The supplied lesson evidence can support an observation, pattern, classroom mechanism, or next-step decision about and MIC lab. It cannot by itself prove causation, establish a real clinical diagnosis, or justify action outside this classroom task.
Reason for review: Your team must decide what the evidence from and MIC lab supports before submitting the labeled and result claim named on the lesson page.
Context: The clear zone around an disk is a measurable readout of drug strength, because a wider zone means the drug stops bacteria at a lower concentration.
- • T1: Put on goggles and gloves and confirm your plate is labeled with each disk.
- • T2: Place disks on the bacterial lawn using .
- • T3: Set the plate to incubate and write what a clear zone around a disk will mean.
- • T4: Once zones form, measure each in millimeters.
- • T5: Rank the antibiotics by zone size and relate larger zones to greater effectiveness.
- • T6: Define MIC and explain how a larger zone hints at a lower MIC.
- • E1: The test measures effectiveness by placing antibiotic-impregnated disks on a bacterial lawn and measuring the clear zone that forms.
- • E2: Because an effective can stop bacteria even where it has diffused to a low concentration, a wider clear zone signals a lower minimum inhibitory concentration and a stronger drug.
- • E3: You will be able to set up a disk-diffusion test safely.
Measurements: Use only the measurements, units, graph, or counts supplied in today's task. No additional patient measurement is implied.
Figure finding: Teaching diagram for and MIC lab. Trace the labeled testing, treatment, or biological process and identify where evidence limits the decision. This is a teaching model, not patient or experimental data.
Uncertainty: This is a composite classroom scenario. Missing history, measurements, or confirmation tests remain unknown and limit the conclusion.
= final volume / sample volume. New concentration = starting concentration / dilution factor.
Mix 1 mL of sample to a final volume of 10 mL. The is 10. A 100 mg/mL starting sample becomes 10 mg/mL.
Use the same volume units before dividing. Concentration keeps its original concentration unit.
Apply the same setup to one supplied dilution or dose. Show the factor, new value, units, and a reasonableness check.
- • The solution must address the stated need in and MIC lab.
- • The decision must be supported by E1-E3.
- • The final product must make the success criteria visible.
- • Complete the work inside the 80-minute block.
- • Use only supplied or teacher-approved materials and evidence.
- • Do not trade , accessibility, or privacy for speed.
- • and evidence quality: must pass before scoring other criteria.
- • User need and effectiveness: highest scored criterion.
- • Time, cost, and ease of use: compare only after and effectiveness pass.
Test evidence: For each option, record the E1-E3 result that supports or fails each criterion. Do not assign a score without a named observation.
- Version or option tested
- Criterion met or missed
- Evidence ID and result
- Revision made
- Reason for the revision
- Need and user
- Criteria and constraints
- Chosen option and evidence
- Test result
- Revision and reason
Students often think Many students think a bigger clear zone means the drug needs a higher dose, since it seems to be doing more work.. The trap: That is a trap because it reverses the relationship. A bigger zone means the drug stopped growth even where it had diffused thin, so it works at a lower concentration, which means a lower minimum inhibitory concentration, not a higher one.
Connection to MIC: a larger zone of inhibition means the antibiotic stopped bacterial growth even where it had spread thin and dilute, which points to a lower minimum inhibitory concentration (less drug needed to work).
Ranking: Antibiotic C (22 mm) was most effective, then A (18 mm), then B (9 mm).
| Antibiotic | Zone of inhibition (mm) | Effectiveness rank |
|---|---|---|
| Antibiotic C | 22 | 1 (most effective) |
| Antibiotic A | 18 | 2 |
| Antibiotic B | 9 | 3 (least effective) |
This model shows the level of evidence and organization needed to complete: A data table listing each antibiotic, its measured zone of inhibition in millimeters, and an effectiveness ranking, with a sentence connecting zone size to minimum inhibitory concentration.
- Name the variables and include units.
- Enter observations without changing the raw values.
- Check labels, calculations, and patterns before interpreting the data.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Bring data table to Thursday's resistance analysis; photograph plate for portfolio.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Tap the speaker to hear a term. Add two of these to your notebook glossary with a definition and an example in your own words.
Pick just 2 or 3 words from today and make them yours: write what each one means in your own words, name the context clue or evidence that helped, then give one example from what you actually did in Disk diffusion and MIC lab. Try your own words first; the glossary is there if you get stuck. This is voluntary and counts as extra credit, so keep it short.
Saved on this device. Show Mr. Mendoza or add these to your notebook glossary to claim the extra credit.
Classroom documents for this lesson are posted in Schoology. Open Clever, then Schoology, and find each one by the name shown on its card.
Open this when the class reaches this activity and use it to complete the required lesson artifact.
Placement rationale
Matched treatment, MIC, resistance by path:Medical-Interventions/Unit-1_How-to-Fight-Infection/1.2_Antibiotic-Treatment; keywords:antibiotic, therapy. Score 142. Visibility: student-schoology (student-facing resource; link through Schoology rather than local path).
Open this when the class reaches this activity and use it to complete the required lesson artifact.
Placement rationale
Matched treatment, MIC, resistance by path:Medical-Interventions/Unit-1_How-to-Fight-Infection/1.2_Antibiotic-Treatment; keywords:antibiotic, resistance. Score 142. Visibility: student-schoology (student-facing resource; link through Schoology rather than local path).
Use this if you were absent, got stuck, or need another pass before you submit the lesson artifact.
Placement rationale
Matched treatment, MIC, resistance by path:Medical-Interventions/Unit-1_How-to-Fight-Infection/1.2_Antibiotic-Treatment; keywords:antibiotic, resistance. Score 138. Visibility: student-schoology (student-facing resource; link through Schoology rather than local path).
How to get there: open Clever and sign in with your Microsoft (district) account. Both myPLTW and Schoology are in Clever. Do the activity in myPLTW. Turn the work in on this site or hand it to Mr. Mendoza, because that is the step that counts as submitted. Schoology only shows your report-card grade later.
Check yourself · commit, then reveal▸
Claim ceiling for this check: The supplied lesson evidence can support an observation, pattern, classroom mechanism, or next-step decision about and MIC lab. It cannot by itself prove causation, establish a real clinical diagnosis, or justify action outside this classroom task.
Drug A leaves a 22 mm clear zone and Drug B leaves a 10 mm zone on the same bacterial lawn. Which drug has the lower MIC, and what does that mean?
Write an answer and pick a confidence to unlock the key.
Fast retrieval with instant answers, not the commit-then-reveal check above. Try each from memory first: write what you remember about the earlier units, then check yourself here.
Go further and get help▸
I can name the procedure's purpose and the evidence I will record. I can identify each named hazard and the control that reduces it: Goggles and gloves on before opening any bacterial culture material; keep on until cleanup is complete. My data table is ready before materials are handled.
Finish the checklist before you handle any material.
- • Goggles and gloves on before opening any bacterial culture material; keep on until cleanup is complete.
- • Treat all bacterial materials as biohazardous: no contact with skin, eyes, or mouth.
- • Open plate lids only briefly and only near the workspace; do not talk, sneeze, or cough over an open plate.
- • Incubate plates inverted (lid down) to prevent condensation dripping onto the lawn.
- • Before disposal: flood plates with 10% bleach solution and seal in a biohazard bag; autoclave if available.
- • Wash hands thoroughly with soap and water after removing gloves.
- 1Before materials are handled, identify the purpose, variables or comparison, controls, measurement units, and stop-work condition.
- 2Put on goggles and gloves and confirm your plate is labeled with each antibiotic disk.
- 3Place antibiotic disks on the bacterial lawn using aseptic technique.
- 4Set the plate to incubate and write what a clear zone around a disk will mean.
- 5Once zones form, measure each zone of inhibition in millimeters.
- 6Rank the antibiotics by zone size and relate larger zones to greater effectiveness.
- 7Define MIC and explain how a larger zone hints at a lower MIC.
- 8Record each result in the prepared table before interpreting it. Mark missing, repeated, or invalid results truthfully.
- 9Complete the named cleanup and waste route, remove PPE safely, wash hands when required, and confirm the station is ready for the next group.
| Trial or sample ID | Independent condition | Measured result with units | Observation before interpretation | Quality-control note |
|---|---|---|---|---|
Before the procedure, predict the result and cite the rule behind the prediction.
After the procedure, compare the result with the prediction and name one limitation or source of uncertainty.
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
If you miss the lab, analyze the teacher disk-diffusion plate images, measure each in millimeters, and submit your ranking of effectiveness.
CDC Antimicrobial Resistance resourcesThen submit your Data table. Turn this in at the drop folder with your district Microsoft sign-in, or hand it to Mr. Mendoza in class. Both count as submitted. Doing the activity in myPLTW does not.
Class still runs. Complete the online activity above (it's self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
CDC Antibiotic Resistance- CompleteEvery required part of the artifact is present, nothing left blank.
- AccurateThe science and the data are correct and match the evidence.
- Scientific reasoningYou explain your claim with evidence and reasoning (CER), not just an answer.
- Professional communicationClear, organized, labeled, and written the way a clinician or scientist would.
- SubmittedTurned in the right way, on the class site or handed to Mr. Mendoza in class, and confirmed. Not in Schoology: that is where the report-card grade appears later.
- Error analysis and method · counts doubleName a specific limit of the method and how it moved your result, and compare what you predicted to what happened. "Human error" does not count; say what about the procedure or instrument caused it.