> For the complete documentation index, see [llms.txt](https://help.sbtinstruments.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.sbtinstruments.com/mpd/workflows/plate-smarter.md). # Plate smarter Plate counts are often done "blind" because the cell concentration is unknown. This leads to excessive and tedious workload. With BactoBox®, you eliminate the guesswork. By knowing the cell concentration, you can target the optimal dilution for plate counts. ## Hit the right dilution for plate counts The illustration below is a typical dilution series for plating.

Dilution series for plate counts. The 15 mL centrifuge vial has a concentration of 1×1010 cells/mL. A 1:10 dilution is prepared by transferring 1 mL sample to 9 mL buffered peptone water (or similar). The lower numbers shows the cells/mL for the individual vials. Eight 1:10 dilutions are needed to get 100 cells per mL. We recommend #bracketing-dilutions. Use the cyan bracket when plating 1 mL. Use the magenta bracket when plating 0.1 mL.

### Petrifilm, compact dry or pour plate method: Plate 1 mL With a culture that has a concentration of 1×1010 cells/mL you should do eight 1:10 dilutions to get the concentration down to 100 cells/mL. This dilution works for [petrifilm](https://www.neogen.com/en/usac/brands/petrifilm/?srsltid=AfmBOool3SFqqwbmN91hw3g2V0cPhRiayV5NKbRTsa9B7JTyTZXXbjpZ), [compact dry](https://www.compact-dry.me/), and [pour plates](https://microbenotes.com/pour-plate-technique-procedure-significance-advantages-limitations/) where 1 mL is added. {% hint style="info" %} ## Rule of thumb for dilutions before petrifilm, compact dry, or pour plate method Use the cells/mL× dil from the BactoBox® measurements to determine the required sample dilution. Write the number with thousand separators and determine how many zeroes to remove to get 25–250 cells per mL. In the example above 8 zeros are removed from 10 000 000 000 to get to 100. That is use 8 dilutions (10-8) prior to plating {% endhint %} ### Spread plate method: Plate 0.1 mL The [spread plate](https://microbenotes.com/?s=spread+plate) method typically only uses 0.1 mL. If you're using this method do one dilution less, i.e. use the seventh dilution instead of eight dilutions. {% hint style="info" %} ## Rule of thumb for dilutions before spread plate method Use the cells/mL× dil from the BactoBox® measurements to determine the required sample dilution. Write the number with thousand separators and determine how many zeros to remove to get 25–250 cells per mL. In the example above 8 zeros are removed from 10 000 000 000 to get to 100. Finally, reduce the number of dilutions by one because only 0.1 mL is plated. That is, use 7 dilutions (10-7) prior to plating. {% endhint %} ## Bracketing dilutions With the above dilution series for plating we assume that the Bactobox® cells/mL is similar to the CFU/mL. As discussed in [Correlation with plate counts](/mpd/cell-growth/correlation-with-plate-counts.md) this is usually a valid assumption. But there are [exceptions](/mpd/cell-growth/divergence-from-plate-counts.md) where BactoBox® cells/mL is either higher or lower than the CFU. Therefore it is often a good idea to "bracket" the dilution series. That is, also do plate counts on the vials next to the assumed optimal dilution. This assumes that the concentrations are within the same log This is exemplified in the above illustration. * When plating 1 mL use the 3 vials in the cyan bracket. * When plating 0.1 mL use the 3 vials in the magenta bracket. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://help.sbtinstruments.com/mpd/workflows/plate-smarter.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.