1/1000

Website: Modified from: https://www.researchgate.net/publication/322213380_Effect_of_the_adhesion_of_Ag_coatings_on_the_effectiveness_and_durability_of_antibacterial_properties/figures?lo=1 

Dr. Spencer: Alright, let's talk about the results from your serial dilutions and which plates you should focus on for counting colonies. Any thoughts, Sam?

Sam: Well, I noticed that some plates have a dense lawn of growth, while others only have a few colonies here and there. I'm not entirely sure which ones we should count.

You: The key is to find plates with a manageable number of colonies. Typically, we aim for plates with 30 to 300 colonies. This range provides a good balance between statistical accuracy and ease of counting.

Dr. Spencer: Indeed. Plates with fewer than 30 colonies can lead to unreliable estimates due to low sample size and possible random distribution errors. Meanwhile, plates with more than 300 colonies are challenging to count accurately and can lead to overlapping colonies, skewing the results.

Sam: I see, in this case the 10^-3 dilution seems to be appropriate. The more concentrated samples (10^-1 and 10^-2) seem to be too crowded and do not have clearly separated colonies to allow accurate counting. And the less diluted sample 10^-4 has a small number of colonies to give statistically significant results. 

Dr. Spencer: Correct. You can count the colonies and use the number to calculate the bacterial concentration. Remember to take into account the dilution factor to back-calculate to the original sample concentration.