Viable plate counts are accurate at which concentration ranges?

Viable plate counts are accurate at which concentration ranges?

• A. Only high concentrations
• B. Only low concentrations
• C. Both high and low concentrations
• D. Neither

Answer: (C)

Viable plate counts are accurate when the plate contains a countable number of colonies, because each colony represents a viable cell (or group) from the original sample. The key is using appropriate dilutions to bring whatever the sample’s concentration is into that reliable range, typically about 30–300 colonies per plate. If the original sample is very concentrated, you dilute it more and still end up with an accurate count on a plate within that window. If the sample is very dilute, you plate with little or no dilution to obtain enough colonies. So, counts can be accurate across a broad range of original concentrations, as long as you select the dilution that yields a plate in the countable range.

Viable plate counts are accurate when the plate contains a countable number of colonies, because each colony represents a viable cell (or group) from the original sample. The key is using appropriate dilutions to bring whatever the sample’s concentration is into that reliable range, typically about 30–300 colonies per plate. If the original sample is very concentrated, you dilute it more and still end up with an accurate count on a plate within that window. If the sample is very dilute, you plate with little or no dilution to obtain enough colonies. So, counts can be accurate across a broad range of original concentrations, as long as you select the dilution that yields a plate in the countable range.