Diluição Seriada (log kill)

Serial dilution is a fundamental laboratory technique in microbiology to determine the concentration of microorganisms in a sample. It involves transferring an aliquot of the sample to a tube containing a diluent, followed by a series of subsequent transfers, each resulting in a greater dilution of the original sample. The goal is to achieve a dilution at which, when seeded on growth plates, results in isolated colonies that can be counted. The basic formula involves dilution by a known factor at each step, usually represented as log₁₀.

The serial dilution process with log kill is especially useful when dealing with samples that contain high concentrations of microorganisms, making it feasible to count colony-forming units (CFU) per milliliter. The log₁₀ approach simplifies calculations, as each dilution is a ten-fold step in reducing concentration. For example, if a sample is diluted 10⁻¹, this means the concentration of microorganisms was reduced by a factor of 10. This method is widely used in microbiological studies, food quality control, and environmental monitoring.

When performing serial dilutions, it is crucial to take care to avoid contamination and ensure the accuracy of the results. This includes proper sterilization of equipment, aseptic execution of transfers, and efficient homogenization of dilutions. In addition, it is essential to consider the choice of diluent, which must be compatible with the microorganism of interest and not interfere with its growth.

The interpretation of results obtained by serial dilution with log kill requires knowledge of experimental conditions and growth characteristics of the microorganism under study. Counting colonies on agar plates properly incubated allows calculation of the original concentration of microorganisms in the sample, applying dilution factors. This calculation is essential for various applications, from assessing the efficacy of antimicrobial agents to determining the microbiological quality of products.