Serial dilution makes dense bacterial populations measurable by reducing the number of cells deposited in each spotted drop. After incubation, colonies can be counted at a selected dilution, and the result is converted to colony-forming units per milliliter using the dilution and measured drop volume. This links a visible plate readout to an estimate of viable bacterial burden.
Each dilution changes the expected colony density, so testing several dilutions increases the chance that at least one spot produces a usable count. The Miles Misra technique places these dilution levels on the same agar plate, reducing the amount of sample and laboratory material required. This design is especially useful when an experiment yields a limited bacterial suspension.
The measured drop is a critical quantitative element, not merely a way to transfer bacteria. Because the deposited volume is known, colony counts can be related back to the original suspension after accounting for dilution. Consistent spotting and clear separation of colonies support interpretable estimates, while poorly chosen dilution levels can make the plate difficult to count.
To process a sample, prepare a series of bacterial dilutions, spot small measured volumes from those dilutions onto agar, incubate the plate, and identify the dilution that provides countable colonies. Record the colony number together with the dilution and drop volume, then use those values to express the result as colony-forming units per milliliter.
In immunology and infection experiments, the method can track bacterial growth or survival under different experimental conditions. It can also quantify antimicrobial activity and reveal infection-related changes in microbial load. Reporting results as colony-forming units per milliliter allows investigators to compare bacterial burden among samples or treatments and relate microbial measurements to infection-associated changes.
A higher or lower colony-forming-unit value provides a quantitative indication that the living bacterial burden differs between samples, treatments, or time points. In this context, the assay can distinguish changes in growth, survival, or reduction associated with antimicrobial activity. Interpretation should remain tied to the dilution and plating record, because the numerical estimate depends on how the sample was processed.