Streak Detective
This wire tool carries bacteria across agar during streaking.
What is an inoculating loop?
Students do this with soap and water before and after handling cultures.
What is handwashing?
A colony's shape, color, and texture are examples of this.
What is colony morphology?
This group provides the baseline for comparison with a treatment.
What is the control group?
In a soap experiment, colony count is the measured outcome. It is this type of variable.
What is the dependent variable?
Three plates have 12, 15, and 18 colonies. Their average is this.
What is 15 colonies?
Skipping loop sterilization between quadrants often produces this continuous, crowded growth.
What is confluent growth?
Accept: a bacterial lawn.
Blowing on a sterile loop can add microbes from this part of the body.
What is the mouth?
Several attached cells grow together into one colony. That colony counts as this many CFUs.
What is one CFU?
A plate receives an unused sterile swab but no sample. No growth is expected from this type of control.
What is a negative control?
Accept: a sterility control.
A team compares different soap brands while keeping amount and contact time equal. This is the independent variable.
What is soap type?
Accept: soap brand.
Untreated samples average 80 colonies; treated samples average 20. The colony count decreased by this percentage.
What is 75 percent?
Only quadrant I grows. The sterile loop never crossed the first streak before starting quadrant II. This connection was missing.
What is overlap?
Accept: overlapping the streaks.
Transferring a microbial sample onto agar is called this.
What is inoculation?
One plate has 10 colonies and another has 50. More colonies do not necessarily mean more of these kinds of bacteria.
What are species?
A control receives bacteria but no sanitizer. Colonies on it confirm that the bacteria can do this.
What is grow?
Accept: form colonies.
Desk samples cover 4 square centimeters; keyboard samples cover 20. This measurement should be equal for a fair comparison.
What is the area sampled?
Plate A has one colony shape. Plate B has four different shapes. This plate shows greater variety in colony morphology.
What is Plate B?
A student takes fresh bacteria from the original sample before every quadrant. This repeated mistake prevents dilution.
What is reloading the loop?
Accept: reinoculating the loop.
Reusing a swab transfers desk microbes into a keyboard sample. This kind of contamination mixes the samples.
What is cross-contamination?
All colonies look alike, but appearance alone cannot confirm this property: having only one species or strain.
What is culture purity?
Accept: a pure culture.
Colonies appear on a sample-free control plate. This is the most likely problem.
What is contamination?
Testing several independent samples for each soap provides this feature, making results more dependable.
What is replication?
Accept: repeated trials.
A team predicts that Soap A will work better. Repeated fair trials favor Soap B. The original hypothesis is supported or this.
What is not supported?
The final streak becomes crowded again after touching quadrant I. This crossing error brought in too many cells.
What is crossing the first streak?
Accept: overlapping quadrant I.
Growing an unknown microbe at room temperature does not prove it is harmless. It might still cause this.
What is disease?
Accept: an infection.
Some living cells cannot grow on the chosen agar. Colony counts can therefore underestimate the total number of these.
What are living cells?
Accept: viable cells.
Neither the sanitizer plate nor the untreated plate grows. The sanitizer's effectiveness cannot be judged, so the result is described by this term.
What is inconclusive?
Soap A is tested only on desks; Soap B only on sinks. This extra variable makes the comparison unfair.
What is surface type?
Accept: sampling location.
A student reports CFU per milliliter but never measures how much liquid sample was used. This measurement is missing.
What is sample volume?