Serial Dilutions Lab Evaluation

Serial dilutions

Done to find out bacterial population in a culture 

Colony on an agar/petri plate

Visible cluster of bacteria that all grew from one single bacterial cell. 

Dilution Factor (DF)

Individual test tube dilution factors. (DF₁ × DF₂ × DF₃ × DF₄)

Final Dilution Factor (FDF)

Final Dilution plated

• FDF = (DF₁ × DF₂ × DF₃ × DF₄) × (final volume plated)

Original Cell Density (OCD)

The number of cells per mL in the original culture. (billions of cells)

• OCD = CFU / FDF
  

“Countable Plate”

A plate with 30–300 colonies.

Colony forming units (CFU)

One colony on a plate that came from one living bacterial cell.

TMTC

Too Many To Count — more than 300 colonies.

TFTC

Too Few To Count — fewer than 30 colonies.

Convergent Growth

When colonies fuse/coalesce because there are too many (above 300). Making counting inaccurate.